Artist's concept of a black hole accreting matter from a star.
|
|
If you're burning more cash than you're accreting value, then there is dilution.
|
|
"This could be a particular behavior of this accreting black hole system," she said.
|
|
Simply put, if you are accreting more value than you burn, there is no dilution.
|
|
The action accelerates as slowly as a stair car, accreting new subplots like hop-ons.
|
|
The current thinking is that galaxies in the early universe grow from accreting gas from the surrounding neighborhood.
|
|
When they're accreting a lot of mass onto the black hole, their accretion disk is quite thin and luminous.
|
|
Most of what astronomers know about supermassive black holes comes from studying black holes that are actively devouring or accreting matter.
|
|
Instead, the script uses his budding relationship with Miriam like the grit that forms a pearl, slowly accreting layers of story around it.
|
|
Artist's impression of the neutron star accreting matter from another star Illustration: ICRAR/University of AmsterdamThis was a fortuitous observation, van den Eijnden explained.
|
|
Jonathan Zittrain: Even though I've been using Facebook for a while, it's as if it knows nothing about me and it starts accreting again.
|
|
A delicate thread of continuity connects these flashes of story, each complete and perfect in and of itself but accreting meaning like nacre on a pearl.
|
|
Slack, a recent technology IPO, exploded in the back half of last decade, accreting huge revenues while burrowing into the tech stacks of the startup world.
|
|
Neural networks aim to mimic the human brain—and one way to think about the brain is that it works by accreting smaller abstractions into larger ones.
|
|
Under Sash Bischoff's busy direction, much of the play's force leaks away in gestures and dances, set to Jared Saltiel's live score, that repeat and repeat without really accreting.
|
|
"The New York Times" is the first to report a story that President Trump&aposs legal team sent a memo to special counsel Robert Mueller in January accreting broad presidential powers.
|
|
"We think that 'The Cow' is the formation of an accreting black hole or neutron star," Giacomo Terreran, observation lead for the Cerro Tololo Inter-American Observatory, said in a statement.
|
|
"Vincent," nearly eight minutes long, is different; it starts out with two minutes of absorbing, slowly accreting Minimalism, with loops of guitar trills, pinging single notes and fleeting sounds running in reverse.
|
|
"We expect to start accreting cash in the second half of the year, and quickly generate significant cash flows in 2019, delivering free cash flow yield approaching 15 percent next year," he said.
|
|
If a black hole that is 10 times as massive as our Sun is accreting at the maximum allowed rate, in about a billion years it could have reached 100 million times the mass of our Sun.
|
|
At the microscopic level, because cash is so highly trafficked, it becomes a sort of palimpsest that records all the hands and back pockets and piggy banks it has passed through, accreting a kind of monetary microbiome.
|
|
To hunt for intermediate-mass black holes, the new study&aposs researchers first analyzed data on about 1 million galaxies in the Sloan Digital Sky Survey , looking for the kind of light typically seen from accreting black holes.
|
|
"Darling" starts with a full minute of wordless instrumental, a three-bar chord progression accreting layers of pretty scales and arpeggios as it repeats, then gives way to a more conventional four-bar pattern that carries the lyrics.
|
|
"There have already been measurements of spins from black holes that are actively accreting," or acquiring more matter under the influence of gravity, the study's first author Dheeraj Pasham, Einstein Postdoctoral Fellow at the MIT Kavli Institute, told Gizmodo.
|
|
They both rest on the hope that within the next week or two, party actors will effectively push three of the four mainline Republican candidates—Marco Rubio, Jeb Bush, Chris Christie, and John Kasich—out of the race by accreting around the other.
|
|
But recently, the litany of corporate missteps and a general sense of power accreting to a few extraordinarily rich and powerful companies and the men–yes, largely men–who lead them has triggered a wave of criticisms of the once-Teflon culture of the Valley.
|
|
"Although globally on average our beaches are accreting, which is good news for holidays and destinations, there are definitely areas that are also eroding," said Arjen Luijendijk, coastal engineer at Delft University of Technology in the Netherlands and one of the authors of the report.
|
|
And "Walt Whitman," the genial, white-bearded representative of democracy, processor of multifarious experience, lover of men and women alike, would become the brand under which the endlessly accreting Leaves of Grass (seven separate editions, in numerous states, before the poet's death in 1892) marketed itself.
|
|
"This work adds to the mounting absence of evidence for accreting white dwarfs as the progenitors of type Ia supernovae," the little-star-eats-big-star scenario, astronomy professor Dan Maoz from Tel-Aviv University, who is not involved in the research, told Gizmodo in an email.
|
|
There are also periodic variations thought to be caused by the appearance and eclipse of the accreting regions during rotation of the white dwarf.
|
|
It is not known what powers ULXs; models include beamed emission of stellar mass objects, accreting intermediate-mass black holes, and super-Eddington emission.
|
|
Some X-ray binaries and active galaxies are able to maintain luminosities close to the Eddington limit for very long times. For accretion-powered sources such as accreting neutron stars or cataclysmic variables (accreting white dwarfs), the limit may act to reduce or cut off the accretion flow, imposing an Eddington limit on accretion corresponding to that on luminosity. Super-Eddington accretion onto stellar-mass black holes is one possible model for ultraluminous X-ray sources (ULXs). For accreting black holes, not all the energy released by accretion has to appear as outgoing luminosity, since energy can be lost through the event horizon, down the hole.
|
|
It is the opposite of the accreting swap. If the swap allows for uncertain contingent ups and downs in the notional principal, it is called a "roller-coaster swap".
|
|
Long term monitoring of the spin period shows small random increases and decreases over time similar to a random walk. The accreting matter causes the random spin period changes.
|
|
Stellar material is being stripped off the secondary and accreting on the primary. R Arae has an 8th-magnitude companion away. The companion star is at a similar distance.
|
|
One low mass member, with spectral type K4.5 is accreting, suggesting the presence of a protoplanetary disk. It is characterised by very low far-IR flux with a high accretion rate.
|
|
M87. Two jets are visible in 3C 31. Relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of light. In an astronomical context, relativistic beaming commonly occurs in two oppositely-directed relativistic jets of plasma that originate from a central compact object that is accreting matter. Accreting compact objects and relativistic jets are invoked to explain x-ray binaries, gamma-ray bursts, and, on a much larger scale, active galactic nuclei (quasars are also associated with an accreting compact object, but are thought to be merely a particular variety of active galactic nuclei, or AGNs).
|
|
One stated that fresh water carries salt from clay particles which is found abundantly in shale and mudstones. The soils at Bario are derived from accreting and non-accretin alluvium, consists of poorly drained clays, podzolic sands, and organic soils. Water-logged soils are suitable for rice cultivation, while better drained non-accreting alluvial soils are suitable for vegetables and citrus fruit cultivation. Bario valley has frequent flash floods because of steep mountain ranges and high surface runoffs.
|
|
Before the accretion is over, the protostar is hidden from view, and therefore not plotted on the color-magnitude diagram. When the envelope finishes accreting, the star is revealed and appears on the birthline.
|
|
Such sources effectively may not conserve energy. Then the accretion efficiency, or the fraction of energy actually radiated of that theoretically available from the gravitational energy release of accreting material, enters in an essential way.
|
|
If ice is present, the reflected waves will be received by a transducer and set ice alert. 10\. Capacitance A total impedance ice detector uses the capacitance of a surface-mounted electrical circuit to determine the presence and thickness of ice and set ice alert. 11\. Optically Occluding An optical source directs radiation at an optical receiver. An accreting surface in close proximity to the beam and accreting ice is senses when ice blocks the path of the beam, and ice alert is set. 12\.
|
|
Sites suggested for the rp-process are accreting binary systems where one star is a neutron star. In these systems the donor star is accreting material onto its compact partner star. The accreted material is usually rich in hydrogen and helium because of its origin from the surface layers of the donor star. Because such compact stars have high gravitational fields, the material falls with a high velocity towards the compact star, usually colliding with other accreted material en route, forming an accretion disk.
|
|
Some of the icy asteroids are also left in orbits crossing the region where the terrestrial planets later formed, allowing water to be delivered to the accreting planets as when the icy asteroids collide with them.
|
|
Masses of its known members vary from 5 Jupiter masses to 2 solar masses, and their spectral types vary from A0 to L7. Some of the best studied members of this stellar association are TW Hydrae (nearest known accreting T Tauri star to the Earth), HR 4796 (an A-type star with resolved dusty debris disk; the most massive known group member), HD 98800 (a quadruple star system with debris disk), and 2M1207 (accreting brown dwarf with remarkable planetary-mass companion 2M1207b). Included in the association is WISEA 1147, which is a brown dwarf.
|
|
Tentsmuir is a key geomorphological site for the study of active beach and coastal processes, in particular those associated with coastal progradation (shoreline building out seawards). The site supports an extensive and relatively undisturbed area of intertidal sand, mudflats and rapidly accreting lime-poor dunes. There are complete sequences of sand dune and slack communities from strandline, saltmarsh, accreting “yellow” dunes, fixed “grey dunes” to lichen rich dune heath, dune slack and dune slack woodland. Associated with these habitats are a large number of plant and invertebrate species including many of national or regional importance.
|
|
47 Tucanae contains hundreds of X-ray sources, including stars with enhanced chromospheric activity due to their presence in binary star systems, cataclysmic variable stars containing white dwarfs accreting from companion stars, and low-mass X-ray binaries containing neutron stars that are not currently accreting, but can be observed by the X-rays emitted from the hot surface of the neutron star. 47 Tucanae has 25 known millisecond pulsars, the second largest population of pulsars in any globular cluster. These pulsars are thought to be spun up by the accretion of material from binary companion stars, in a previous X-ray binary phase. The companion of one pulsar in 47 Tucanae, 47 Tuc W, seems to still be transferring mass towards the neutron star, indicating that this system is completing a transition from being an accreting low-mass X-ray binary to a millisecond pulsar.
|
|
AM CVn variables are symbiotic binaries where a white dwarf is accreting helium-rich material from either another white dwarf, a helium star, or an evolved main-sequence star. They undergo complex variations, or at times no variations, with ultrashort periods.
|
|
The opposite of an accretion disk is an excretion disk where instead of material accreting from a disk on to a central object, material is excreted from the center outwards on to the disk. Excretion disks are formed when stars merge.
|
|
The nebulae is a mystery as the variations in nebulae brightness appear to be unrelated to the host star. One theory is that rather than being an accreting protoplanetary disk the star may be an evolved star that is losing material.
|
|
In 1991, with the rediscovery of the magnetorotational instability (MRI), S. A. Balbus and J. F. Hawley established that a weakly magnetized disk accreting around a heavy, compact central object would be highly unstable, providing a direct mechanism for angular-momentum redistribution.
|
|
One way to gain the additional mass would be by accreting gas from a giant star (or even main sequence) companion. A second and apparently more common mechanism to generate the same type of explosion is the merger of two white dwarfs.
|
|
Scorpius XR-1 has been observed at J1950 RA Dec . In 1967 (before the discovery of pulsars), Iosif Shklovsky examined X-ray and optical observations of Scorpius X-1 and correctly concluded that the radiation comes from a neutron star accreting matter from a companion.
|
|
Hercules X-1 (Her X-1), also known as 4U1656+35, is a moderately strong X-ray binary source first studied by the Uhuru satellite. It is composed of a neutron star accreting matter from a normal star (HZ Her) probably due to Roche lobe overflow.
|
|
3C75 (a.k.a. 3C 75) is a binary black hole system in the Abell 400 cluster of galaxies. It has four radio jets (two from each accreting black hole). It is travelling at 1200 kilometers per second through the cluster plasma, causing the jets to be swept back.
|
|
The core of this system is called a protostar. Some of the accreting material is ejected out along the star's axis of rotation in two jets of partially ionised gas (plasma). The mechanism for producing these collimated bipolar jets is not entirely understood, but it is believed that interaction between the accretion disk and the stellar magnetic field accelerates some of the accreting material from within a few astronomical units of the star away from the disk plane. At these distances the outflow is divergent, fanning out at an angle in the range of 10−30°, but it becomes increasingly collimated at distances of tens to hundreds of astronomical units from the source, as its expansion is constrained.
|
|
He also envisioned accreting large aquadynamic OTEC ocean thermal energy conversion plants, both for generating power and for producing hydrogen, ammonia, and magnesium hydroxide. This appeared to result in a building process largely independent of land-based resources. His focus shifted to coral reefs after meeting Thomas J. Goreau in the 1980s.
|
|
Little is known about the components of LL Andromedae because it's a faint object; one of the two components is likely an accreting white dwarf like in all dwarf novae. A brown dwarf donor has been proposed, but the short periodicity of superhumps hints instead at the presence of a massive companion.
|
|
The merger process of two co-orbiting white dwarfs produces gravitational waves If a white dwarf is in a binary star system and is accreting matter from its companion, a variety of phenomena may occur, including novae and Type Ia supernovae. It may also be a super-soft x-ray source if it is able to take material from its companion fast enough to sustain fusion on its surface. On the other hand, phenomena in binary systems as tidal interaction and star-disc interaction, moderated by magnetic fields or not, act on the rotation of accreting white dwarfs. In fact, the fastest-spinning, securely known white dwarfs, are members of binary systems (being the white dwarf in CTCV J2056-3014 the fastest one).
|
|
Simulations have shown that gas accreting onto supermassive black holes in galactic centers produces high-energy jets; the released energy can expel enough cold gas to quench star formation. Our own Milky Way and the nearby Andromeda Galaxy currently appear to be undergoing the quenching transition from star-forming blue galaxies to passive red galaxies.
|
|
SAX J1808.4-3658 is a transient, accreting millisecond X-ray pulsar that is intermittent. In addition, X-ray burst oscillations and quasi- periodic oscillations in addition to coherent X-ray pulsations have been seen from SAX J1808.4-3658, making it a Rosetta stone for interpretation of the timing behavior of low-mass X-ray binaries.
|
|
RX Andromedae is a cataclysmic variable system, where a white dwarf with a mass of 0.8 and an M2 main sequence star are rotating around their center of mass. The main sequence star is overfilling its Roche lobe, so the white dwarf is stripping away matter from the companion star and accreting it through an accretion disk.
|
|
Located near Eta Cygni is the X-ray source Cygnus X-1, which is now thought to be caused by a black hole accreting matter in a binary star system. This was the first x-ray source widely believed to be a black hole. The two component stars of Albireo are easily distinguished, even in a small telescope.
|
|
The primary component has a spectral type of M4.5 and a red apparent magnitude of 14.2. Both components seem to be accreting mass from their stellar disks, as shown by their emission lines. The four stars have a total mass of only 26% of the Sun, making it the quadruple star system with the lowest mass known.
|
|
The rhizomes tolerate submersion in sea water and can break off and float in the currents to establish the grass at new sites. The leaves are up to long and sharply pointed. The cylindrical inflorescence is up to long. It is adapted to habitat made up of shifting, accreting sand layers, as well as that composed of stabilised dunes.
|
|
The Herschel infra-red telescope's image shows an embryonic star that is likely to become one of the brightest stars in our Galaxy at some time within the next few hundred thousand years. The star now appears about ten times more massive than the Sun and may grow much larger by accreting material from the surrounding gas and dust.
|
|
In 2004, Haggard received a Master of Science in Physics from San Francisco State University, where studied X-ray-emitting binary stars in the globular cluster Omega Centauri. She received a Ph.D. in Astronomy from the University of Washington in 2010. Her thesis work focused on active galactic nuclei (accreting supermassive black holes at the center of distant galaxies).
|
|
This results in vertical deformation manifest in the mountainous terrain of Hispaniola. Some researchers believe that the EPGFZ and the Septentrional-Orient fault zone bound a microplate, dubbed the Gonâve Microplate, a area of the northern Caribbean Plate that is in the process of shearing off the Caribbean Plate and accreting to the North America Plate.
|
|
A similar process, known as the giant impact hypothesis, has been proposed to explain the formation of the Moon. Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had stabilized. It would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and possibly even as high as 10,000 K. Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" that could have been carried away by the solar wind. A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material and not gathered by Mercury.
|
|
The AM Herculis binary system contains a white dwarf and a red dwarf. The white dwarf is accreting material directly from the red dwarf without an accretion disk. The white dwarf primary is highly magnetic and the infalling material is channelled towards the magnetic poles. The accretion rate is unstable, at times decreasing dramatically and reducing the brightness of the whole system.
|
|
The Eddington limit is invoked to explain the observed luminosity of accreting black holes such as quasars. Originally, Sir Arthur Eddington took only the electron scattering into account when calculating this limit, something that now is called the classical Eddington limit. Nowadays, the modified Eddington limit also counts on other radiation processes such as bound-free and free-free radiation (see Bremsstrahlung) interaction.
|
|
Another class of cataclysmic variables with magnetic white dwarfs accreting material from a main sequence donor star are the intermediate polars. These have less strong magnetic fields and the rotation of the white dwarf is not synchronised with the orbital period. It has been proposed that intermediate polars may evolve into polars as the donor is depleted and the orbit shrinks.
|
|
This disk has a mass of at least 10 Earth masses. Observations with the SINFONI spectrograph at the Very Large Telescope show that the disk is accreting matter at the rate of approximately 10−11 of the mass of the Sun per year. It could eventually develop into a planetary system. Observations with ALMA detected the disk in millimeter wavelengths.
|
|
Geologically, the Lesser Antilles island arc stretches from Grenada in the south to Anguilla in the north. The Virgin Islands and Sombrero Island are geologically part of the Greater Antilles, while Trinidad is part of South America and Tobago is the remainder of a separate island arc. The Leeward Antilles are also a separate island arc, which is accreting to South America.
|
|
Semidetached binary stars are binary stars where one of the components fills the binary star's Roche lobe and the other does not. Gas from the surface of the Roche-lobe- filling component (donor) is transferred to the other, accreting star. The mass transfer dominates the evolution of the system. In many cases, the inflowing gas forms an accretion disc around the accretor.
|
|
AK Scorpii is a Herbig Ae/Be star and spectroscopic binary star about 459 light-years distant in the constellation Scorpius. The star belongs to the nearby Upper Centaurus–Lupus star-forming region and the star is actively accreting material. The binary is surrounded by a circumbinary disk that was imaged with VLT/SPHERE in scattered light and with ALMA.
|
|
In these deposits, mixed reddish-brown sands and silts dominate with minor mudstones and conglomerates interspersed. Interpreted channel deposits grade from laterally accreting coarse sands - into conglomerates of pebble-sized carbonate clasts. Channels are 0.5 meter to 7 meters thick and may extend laterally for a few hundred meters. Fine-grained silt to mudstone deposits are proximal to interpreted channels.
|
|
179:433-456 (1977). This mechanism correctly describes how astrophysical jets are formed around spinning supermassive black holes. This is one of the mechanisms that power quasars, or rapidly accreting supermassive black holes. Generally speaking, it was demonstrated that the power output of the accretion disk is significantly larger than the power output extracted directly from the hole, through its ergosphere.
|
|
At least one ULX source, Holmberg II X-1, has been observed in states with spectra characteristic of both the high and low state. This suggests that some ULXs may be accreting IMBHs (see Winter, Mushotzky, Reynolds 2006). Background quasars — A significant fraction of observed ULXs are in fact background sources. Such sources may be identified by a very low temperature (e.g.
|
|
Athena will perform very sensitive measurements on a wide range of celestial objects. It will investigate the chemical evolution of the hot plasma permeating the intergalactic space in cluster of galaxies, search for elusive observational features of the Warm-Hot Intergalactic Medium, investigate powerful outflows ejected from accreting black holes across their whole mass spectrum, and study their impact on the host galaxy, and identify sizeable samples of comparatively rare populations of Active Galactic Nuclei (AGN) that are key to understanding the concurrent cosmological evolution of accreting black holes and galaxies. Among them are highly obscured and high-redshift (z≥6) AGN. Furthermore, Athena will be an X-ray observatory open to the whole astronomical community, poised to provide wide-ranging discoveries in almost all fields of modern astrophysics, with a large discovery potential of still unknown and unexpected phenomena.
|
|
Deuterium is the most easily fused nucleus available to accreting protostars, and such fusion in the center of protostars can proceed when temperatures exceed 106 K. The reaction rate is so sensitive to temperature that the temperature does not rise very much above this. The energy generated by fusion drives convection, which carries the heat generated to the surface. If there were no deuterium available to fuse, then stars would gain significantly less mass in the pre-main-sequence phase, as the object would collapse faster, and more intense hydrogen fusion would occur and prevent the object from accreting matter. Deuterium fusion allows further accretion of mass by acting as a thermostat that temporarily stops the central temperature from rising above about one million degrees, a temperature not high enough for hydrogen fusion, but allowing time for the accumulation of more mass.
|
|
X-ray bursters are one class of X-ray binary stars exhibiting periodic and rapid increases in luminosity (typically a factor of 10 or greater) that peak in the X-ray regime of the electromagnetic spectrum. These astrophysical systems are composed of an accreting compact object, and a main sequence companion 'donor' star. A compact object in an X-ray binary system consists of either a neutron star or a black hole; however, with the emission of an X-ray burst, the companion star can immediately be classified as a neutron star, since black holes do not have a surface and all of the accreting material disappears past the event horizon. The donor star's mass falls to the surface of the neutron star where the hydrogen fuses to helium which accumulates until it fuses in a burst, producing X-rays.
|
|
Early work on exoplanets was not well funded, and Haswell has spoken about using second hand Canon camera lenses to make suitable telescopes. First working on accreting binary stars, and then exoplanets. In particular, Haswell studies short period exoplanets. Since 2012 she has led the Dispersed Matter Planet Project, which involves the analysis of light from nearby stars to identify which host mass- losing planets.
|
|
Elliptical galaxies have central supermassive black holes, and the masses of these black holes correlate with the galaxy's mass. Elliptical galaxies have two main stages of evolution. The first is due to the supermassive black hole growing by accreting cooling gas. The second stage is marked by the black hole stabilizing by suppressing gas cooling, thus leaving the elliptical galaxy in a stable state.
|
|
It is classified as an active galaxy because the supermassive black hole at its nucleus is accreting matter, which produces two jets of matter from the poles. The jets' interaction with the interstellar medium creates radio lobes, one source of radio emissions. Cygnus is also the apparent source of the WIMP-wind due to the orientation of the solar system's rotation through the galactic halo.
|
|
In recent years, greater knowledge of processes along convergent plate boundaries has caused skepticism about this simplistic model. Observations indicate convergent boundaries typically display oblique motion. The implications of such observations demonstrate the possibility that metamorphic belts could have formed in different sectors of the same subduction margin and became juxtaposed afterwards. Furthermore, accreting allochthonous terrains along subduction zones as a mechanism, encourages the skepticism.
|
|
Inverse Compton scattering is important in astrophysics. In X-ray astronomy, the accretion disk surrounding a black hole is presumed to produce a thermal spectrum. The lower energy photons produced from this spectrum are scattered to higher energies by relativistic electrons in the surrounding corona. This is surmised to cause the power law component in the X-ray spectra (0.2–10 keV) of accreting black holes.
|
|
These pulsations occur when a relativistic beam from the white dwarf sweeps across the red dwarf, which then reprocesses the beam into the observed electromagnetic energy. At present, the white dwarf is not accreting significantly, and the system is powered by the spin-down of the white dwarf. The pulsar is about the same size as Earth. AR Sco's unusual nature was first noticed by amateur astronomers.
|
|
Beach evolution occurs at the shoreline where sea, lake or river water is eroding the land. Beaches exist where sand accumulated from centuries-old, recurrent processes that erode rocky and sedimentary material into sand deposits. River deltas deposit silt from upriver, accreting at the river's outlet to extend lake or ocean shorelines. Catastrophic events such as tsunamis, hurricanes, and storm surges accelerate beach erosion.
|
|
The effect can be more complex in cases where the axis of rotation is not perpendicular to the orbital plane. For contact or semi-detached binaries, the transfer of mass from a star to its companion can also result in a significant transfer of angular momentum. The accreting companion can spin up to the point where it reaches its critical rotation rate and begins losing mass along the equator.
|
|
The relative masses of the Jovian moons. Those smaller than Europa are not visible at this scale, and combined would only be visible at 100× magnification. Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk. They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history.
|
|
Further observations by Swift Observatory confirmed its Compton-thick nature. The source of activity in the active galactic nuclei is a supermassive black hole (SMBH) lying at the centre of the galaxy. The SMBH at the centre of NGC 4939 is accreting material with a rate of 0.077 per year. The black hole has been detected in hard X-rays, which are not absorbed by the Compton-thick column, by INTEGRAL.
|
|
The relative masses of the Jovian moons. Those smaller than Europa are not visible at this scale, and combined would only be visible at 100× magnification. Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of accreting gas and solid debris analogous to a protoplanetary disk. They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history.
|
|
Thermal radiation from the cathode heats the grid. As a result, low-work-function cathode material evaporates and condenses on the grid. This eventually leads to a short between cathode and grid, as the material accreting on the grid narrows the gap between it and the cathode. In addition, the emissive cathode material on the grid causes a negative grid current (reverse electron flow from the grid to the cathode).
|
|
A total of thirteen accreting millisecond X-ray pulsars have been discovered as of January 2011. Three of them are Intermittent millisecond X-ray pulsars (HETE J1900.1-2455, Aql X-1 and SAX J1748.9-2021), i.e. they emit pulsations sporadically during the outburst. On 21 August 2019 (UTC; 20 August in the US), Neutron Star Interior Composition Explorer (NICER) spotted the brightest X-ray burst so far observed.
|
|
Polar variables are magnetic white dwarfs accreting material from a low mass donor, with no accretion disk due to the intense magnetic field A Polar is a highly magnetic type of cataclysmic variable binary star system, originally known as an AM Herculis star after the prototype member AM Herculis. Like other cataclysmic variables (CVs), polars contain two stars: an accreting white dwarf (WD), and a low-mass donor star (usually a red dwarf) which is transferring mass to the WD as a result of the WD's gravitational pull, overflowing its Roche lobe. Polars are distinguished from other CVs by the presence of a very strong magnetic field in the WD. Typical magnetic field strengths of polar systems are 10 million to 80 million gauss (1000-8000 teslas). The WD in the polar AN Ursae Majoris has the strongest known magnetic field among cataclysmic variables, with a field strength of 230 million gauss (23 kT).
|
|
The CBSS model invokes steady nuclear burning on the surface of an accreting white dwarf (WD) as the generator of the prodigious super soft X-ray flux. As of 1999, eight SSXSs have orbital periods between ~4 hr and 1.35 d: RX J0019.8+2156 (MW), RX J0439.8-6809 (MW halo near LMC), RX J0513.9-6951 (LMC), RX J0527.8-6954 (LMC), RX J0537.7-7034 (LMC), CAL 83 (LMC), CAL 87 LMC), and 1E 0035.4-7230 (SMC).
|
|
A supermassive black hole at the core of a galaxy may serve to regulate the rate of star formation in a galactic nucleus. A black hole that is accreting infalling matter can become active, emitting a strong wind through a collimated relativistic jet. This can limit further star formation. Massive black holes ejecting radio-frequency-emitting particles at near-light speed can also block the formation of new stars in aging galaxies.
|
|
Govert Schilling 6 July 1996 In 2006, R. E. Schild suggested that the accreting object at the heart of Q0957+561 is not a supermassive black hole, as is generally believed for all quasars, but a magnetospheric eternally collapsing object. Schild's team at the Harvard- Smithsonian Center for Astrophysics asserted that "this quasar appears to be dynamically dominated by a magnetic field internally anchored to its central, rotating supermassive compact object" (R. E. Schild).
|
|
The sandstones of the LEF mainly comprise laterally accreting channel deposits that are multi-story and contain trough, low angle, and planar, cross-bedding. Ripple cross laminations with good horizontal lamination are also present. In the UEF, sandstone beds are single story and mainly reflect downstream accretion channel geometries and are more tabular in appearance. Common internal sedimentary structures of UEF sandstones are planar, low angle cross-bedding, horizontal and ripple-cross laminations.
|
|
This system is located around 15,500 light-years away from Earth. A recurrent nova, it has brightened to the 7th magnitude in the years 1890, 1902, 1920, 1944, 1966 and 2011 from a baseline of around 14th magnitude. These outbursts are thought to be due to the white dwarf accreting material from its companion and ejecting periodically. TY Pyxidis is an eclipsing binary star whose apparent magnitude ranges from 6.85 to 7.5 over 3.2 days.
|
|
The blue progenitor system of the type-Iax supernova 2012Z in the spiral galaxy NGC 1309 is similar to the progenitor of the Galactic helium nova V445 Puppis, suggesting that SN 2012Z was the explosion of a white dwarf accreting from a helium-star companion. It is observed to have caused a growing helium star that has the potential to transform into a red giant after losing its hydrogen envelope in the future.
|
|
Those with luminosities below ~3 x 1038 erg/s are consistent with steady nuclear burning in accreting white dwarfs (WD)s or post-novae. There are a few SSS with luminosities ≥1039 erg/s. Super soft X-rays are believed to be produced by steady nuclear fusion on a white dwarf's surface of material pulled from a binary companion, the so-called close-binary supersoft source (CBSS). This requires a flow of material sufficiently high to sustain the fusion.
|
|
4U 1700-37 is one of the stronger binary X-ray sources in the sky, and is classified as a high-mass X-ray binary. It was discovered by the Uhuru satellite. The "4U" designation refers to the Fourth (and final) Uhuru catalog. It is associated with a bright (6.53 V magnitude) blue supergiant star HD 153919, which is orbited by an accreting compact object that must be either a neutron star or a black hole.
|
|
Down are some famous objects in this cluster: NGC 1365 is another barred spiral galaxy located at a distance of 56 million light-years from Earth. Like NGC 1097, it is also a Seyfert galaxy. Its bar is a center of star formation and shows extensions of the spiral arms' dust lanes. The bright nucleus indicates the presence of an active galactic nucleus – a galaxy with a supermassive black hole at the center, accreting matter from the bar.
|
|
During IXPE's two- year mission, it will study targets such as active galactic nuclei, quasars, pulsars, pulsar wind nebulae, magnetars, accreting X-ray binaries, supernova remnants, and the Galactic Center. The spacecraft is being built by Ball Aerospace. The principal investigator is Martin C. Weisskopf of NASA Marshall Space Flight Center; he is the chief scientist for X-ray astronomy at NASA's Marshall Space Flight Center and project scientist for the Chandra X-ray Observatory spacecraft.
|
|
D. Clayton, New Astronomy Reviews 55, 155–65 (2011), section 5.5, p. 163] According to that principle rapid oxidation actually intensifies growth of large grains of carbon by keeping the population of carbon solids small so that those few can grow large by accreting the continuously replenished free carbon. This topic establishes another new aspect of carbon's uniquely versatile chemistry. Their 2017 paper also computes the abundances of molecules and of Buckminsterfullerene grains ejected along with the graphite grains.
|
|
As a galaxy falls into a galaxy cluster, gravitational interactions with other galaxies can strangle it by preventing it from accreting more gas. For galaxies with massive dark matter halos, another preventive mechanism called “virial shock heating” may also prevent gas from becoming cool enough to form stars. Ejective processes, which expel cold gas from galaxies, may explain how more massive galaxies are quenched. One ejective mechanism is caused by supermassive black holes found in the centers of galaxies.
|
|
During early stages of formation, stars launch bipolar outflows of partially ionized material along the rotation axis. It is generally believed that the interaction of accretion disk magnetic fields with stellar magnetic fields propels some of the accreting material in the form of outflows. In some cases, outflow is collimated into jets. The source of HH 46/47 is a binary class I protostar located inside a dark cloud of gas and dust, undetectable at visual wavelengths.
|
|
This period was far shorter than astronomers considered pulsars capable of reaching, and led to the suggestion that pulsars can be spun-up by accreting mass from a companion. The rotation of PSR B1937+21, along with other millisecond pulsars discovered later, are very stable in their rotation. They are capable of keeping time as well as atomic clocks. PSR B1937+21 is unusual in that it is one of few pulsars which occasionally emits particularly strong pulses.
|
|
TW Hydrae is a T Tauri star approximately 196 light-years away in the constellation of Hydra (the Sea Serpent). The star is the closest such star to the Solar System. TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old. The star appears to be accreting from a face-on protoplanetary disk of dust and gas, which has been resolved in images from the ALMA observatory.
|
|
In 2000, this distance was revised to after correcting for probable errors. The Gaia spacecraft later measured the parallax of the star leading to an accurate distance of parsecs. The nova outburst can be explained by a white dwarf that is accreting matter from a companion; most likely a low-mass main sequence star. This close binary system has an orbital period of 1.47 hours, which is one of the shortest periods of the known classical nova.
|
|
Portion of North Africa that rifted to form Greater Adria The continent formed by rifting from the north Africa portion of the supercontinent of Gondwanaland 240 million years ago. It broke free into the Neo-Tethys Ocean and headed towards Laurasia. About 200 million years ago, the microcontinent of Iberia separated from the bulk of Greater Adria. The continent ended up accreting to the south Europe portion of the supercontinent of Laurasia, 140 million years ago.
|
|
Under these conditions considerable ionization would be present and the gas would be accelerated by magnetic fields, hence the angular momentum could be transferred from the Sun. He postulated that these lunar-size bodies were destroyed by collisions, with the gas dissipating, leaving behind solids collected at the core, with the resulting smaller fragments pushed far out into space and the larger fragments staying behind and accreting into planets. He suggested the Moon was just such a surviving core.
|
|
In 1994, Haswell moved to Columbia University, where she worked on black hole X-ray transients and cataclysmic variable stars. She was made a lecturer at the Barnard College where one of her students was Lauryn Hill. Haswell moved back to the United Kingdom in 1996 and was made a lecturer at the University of Sussex. Since 1999, she has been at the Open University, at first still working on black holes and accreting binary stars and switching to exoplanet research in 2003.
|
|
The Acadian orogeny experienced at least three major phases of deformation, and in places, unconformities were recognized. These phases were called tectophases, and represented the sequence of collisions that occurred from the Avalonian terranes accreting to Laurentia. As a result of these tectophases, deltas developed on the adjacent parts of the stable craton, eastern margin of Laurentia. These deltas are described as foreland-basin, delta-complex clastic wedges, which are responsible for the large volumes of sediment input into the Appalachian basin.
|
|
The name "Haüy octahedral number" comes from the work of René Just Haüy, a French mineralogist active in the late 18th and early 19th centuries. His "Haüy construction" approximates an octahedron as a polycube, formed by accreting concentric layers of cubes onto a central cube. The centered octahedral numbers count the number of cubes used by this construction. Haüy proposed this construction, and several related constructions of other polyhedra, as a model for the structure of crystalline minerals.. See in particular p.
|
|
AG Pegasi has been described as the slowest nova ever recorded, with a constant bolometric luminosity of the hotter star over 130 years from 1850 to 1980. By the late 20th century, the hotter star has evolved into a hot subdwarf on its way to eventually returning to white dwarf status. Vogel and colleagues calculated the hotter star must have been accreting material from the red giant for around 5000 years before erupting. Both stars are ejecting material in stellar winds.
|
|
There is evidence of star formation, but that has nearly ceased in the nuclear region due to the molecular gas being all but exhausted. The nuclear bar, if it exists, now consists of stars with little surrounding gas. This is a Seyfert galaxy of type 1.9, indicating it has an obscured active galactic nucleus (AGN) powered by a supermassive black hole at the center. The estimated mass of this object is and it is accreting mass at the rate of .
|
|
The cometary and asteroidal delivery of water to accreting Earth and Mars has significant caveats, even though it is favored by D/H isotopic ratios. Key issues include: # The higher D/H ratios in Martian meteorites could be a consequence of biased sampling since Mars may have never had an effective crustal recycling process # Earth's Primitive upper mantle estimate of the 187Os/188Os isotopic ratio exceeds 0.129, significantly greater than that of carbonaceous chondrites, but similar to anhydrous ordinary chondrites.
|
|
There are also sporadic X-ray off durations. The spin period history of Centaurus X-3 shows a spin-up trend that is very prominent in the long term decrease in its pulse period. This spin-up was first noted in Centaurus X-3 and Hercules X-1 and is now noted in other X-ray pulsars. The most feasible way of explaining the origin of this effect is by a torque exerted on the neutron star by accreting material.
|
|
An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate mass star. Hercules X-1 is composed of a neutron star accreting matter from a normal star (HZ Her) probably due to Roche lobe overflow. X-1 is the prototype for the massive X-ray binaries although it falls on the borderline, , between high- and low-mass X-ray binaries.
|
|
After earning a distinction in the Mathematical Tripos, Lynden-Bell went on to doctoral studies in theoretical astronomy working with Leon Mestel, which he completed in 1960. In 1962, he published research with Olin Eggen and Allan Sandage arguing that the Milky Way originated through the dynamic collapse of a single large gas cloud. In 1969 he published his theory that quasars are powered by massive black holes accreting material. From counting dead quasars, he deduced that most massive galaxies have black holes at their centres.
|
|
High-mass X-ray binaries (HMXBs) are composed of OB supergiant companion stars and compact objects, usually neutron stars (NS) or black holes (BH). Supergiant X-ray binaries (SGXBs) are HMXBs in which the compact objects orbit massive companions with orbital periods of a few days (3–15 d), and in circular (or slightly eccentric) orbits. SGXBs show typical the hard X-ray spectra of accreting pulsars and most show strong absorption as obscured HMXBs. X-ray luminosity (Lx) increases up to 1036 erg·s−1 (1029 watts).
|
|
Since the spectral classification of PX Andromedae is peculiar and similar to U Geminorum, it's commonly accepted that in this system a white dwarf is accreting matter from a donor star, and an accretion disc has formed around the former. The negative superhumps show that the accretion disk is tilted with respect to the white dwarf rotation axis, and has a retrogade precession. Moreover, the donor star doesn't eclipse the central part of the disk, otherwise there wouldn't be any modulation of the eclipse depth.
|
|
The disk has a radius of about 370 astronomical units (au) with about 40 Earth masses of dust in the disk. V4046 Sagittarii is one of four pre-main-sequence star systems within 100 parsecs with protoplanetary disks, the others being TW Hydrae, HD 141569, and 49 Ceti. The two stars are still accreting matter from the disk, and gas giant planets may be forming in the disk as well. The red dwarf binary GSC 07396-00759 is separated about 2.82″ from V4046 Sagittarii.
|
|
RS Ophiuchi has flared into a (recurrent) nova on at least six occasions, each time accreting the critical mass of hydrogen needed to produce a runaway explosion. It is possible that IK Pegasi B will follow a similar pattern. In order to accumulate mass, however, only a portion of the accreted gas can be ejected, so that with each cycle the white dwarf would steadily increase in mass. Thus, even should it behave as a recurring nova, IK Pegasus B could continue to accumulate a growing envelope.
|
|
Observations with the Chandra X-ray Observatory have identified 83 X-ray sources, including a source located at the nucleus. The brightest of these sources may be an intermediate-mass black hole that is accreting matter. The galaxy is also emitting a diffuse soft X-ray radiation within 10 kpc of the optical galaxy. The spectrum of the X-ray source at the core is consistent with an active galactic nucleus, but an examination with the Spitzer Space Telescope shows no indication of activity.
|
|
Nucleosynthesis of proton-rich nuclei by rapid proton capture The rp-process (rapid proton capture process) consists of consecutive proton captures onto seed nuclei to produce heavier elements.Lars Bildsten, "Thermonuclear Burning on Rapidly Accreting Neutron Stars" in The Many Faces of Neutron Stars, ed. R. Buccheri, J. van Paradijs, & M. A. Alpar (Kluwer), 419 (1998). It is a nucleosynthesis process and, along with the s-process and the r-process, may be responsible for the generation of many of the heavy elements present in the universe.
|
|
North Hutchinson is an Atlantic barrier island located on Florida's Treasure Coast approximately north of Fort Lauderdale. State Road A1A is the main road for the length of the island, and four bridges provide access to the mainland. For most of its length, A-1-A is known as Atlantic Beach Boulevard.Map 1998, Fort Lauderdale, Dolph Map Co. North Hutchinson Island has many county and state parks and preserves, and is one of the few areas on the east coast of Florida with several accreting (growing) beaches.
|
|
The system of DX Andromedae consists of a white dwarf accreting matter from a donor star through an accretion disk. The system shows a spectral type at quiescence of K1 V (plus emission lines), but the donor is considered to be a hydrogen- deficient star that has evolved off the main sequence and is overfilling its roche lobe. The donor star dominates the visible spectrum during the quiescent phase. The spectral classification of DX Andromedae as a whole is classified as peculiar of the U Geminorum type.
|
|
In particular, active galactic nuclei and quasars are believed to be the accretion disks of supermassive black holes. Similarly, X-ray binaries are generally accepted to be binary star systems in which one of the two stars is a compact object accreting matter from its companion. It has also been suggested that some ultraluminous X-ray sources may be the accretion disks of intermediate-mass black holes. In November 2011 the first direct observation of a quasar accretion disk around a supermassive black hole was reported.
|
|
Ecological succession is generally defined as the successive occupation of a site by different plant communities. In an accreting mudflats the outer community along the sequence represents the pioneer community which is gradually replaced by the next community representing the seral stages and finally by a climax community typical of the climatic zone. Robert Scott Troup suggested that succession began in the newly accreted land created by fresh deposits of eroded soil. The pioneer vegetation on these newly accreted sites is Sonneratia, followed by Avicennia and Nypa.
|
|
The remains of the Farallon Plate are the Juan de Fuca, Explorer and Gorda Plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate. The Farallon Plate is also responsible for transporting old island arcs and various fragments of continental crustal material rifted off from other distant plates and accreting them to the North American Plate. These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). Much of western North America is composed of these accreted terranes.
|
|
The Saturnian moon Rhea may have a tenuous ring system consisting of three narrow, relatively dense bands within a particulate disk, the first predicted around a moon. Most rings were thought to be unstable and to dissipate over the course of tens or hundreds of millions of years. Studies of Saturn's rings however indicate that they may date to the early days of the Solar System. Current theories suggest that some ring systems may form in repeating cycles, accreting into natural satellites that break up as soon as they reach the Roche limit.
|
|
Novae are also the result of dramatic explosions, but unlike supernovae do not result in the destruction of the progenitor star. Also unlike supernovae, novae ignite from the sudden onset of thermonuclear fusion, which under certain high pressure conditions (degenerate matter) accelerates explosively. They form in close binary systems, one component being a white dwarf accreting matter from the other ordinary star component, and may recur over periods of decades to centuries or millennia. Novae are categorised as fast, slow or very slow, depending on the behaviour of their light curve.
|
|
Use of the term "accretion disk" for the protoplanetary disk leads to confusion over the planetary accretion process. The protoplanetary disk is sometimes referred to as an accretion disk, because while the young T Tauri-like protostar is still contracting, gaseous material may still be falling onto it, accreting on its surface from the disk's inner edge. In an accretion disk, there is a net flux of mass from larger radii toward smaller radii. However, that meaning should not be confused with the process of accretion forming the planets.
|
|
As the collapse continues, the rotation rate can increase to the point where the accreting protostar can break up due to centrifugal force at the equator. Thus the rotation rate must be braked during the first 100,000 years of the star's life to avoid this scenario. One possible explanation for the braking is the interaction of the protostar's magnetic field with the stellar wind. In the case of our own Sun, when the planets' angular momenta are compared to the Sun's own, the Sun has less than 1% of its supposed angular momentum.
|
|
Further observations have revealed that some Bok globules contain embedded warm sources, some contain Herbig–Haro objects, and some show outflows of molecular gas. Millimeter-wave emission line studies have provided evidence for the infall of material onto an accreting protostar. It is now thought that a typical Bok globule contains about 10 solar masses of material in a region about a light-year or so across, and that Bok globules most commonly result in the formation of double- or multiple-star systems. Bok globules are still a subject of intense research.
|
|
Among his highest citation scientific papers are the discovery and collaborative study of an atypical supernova observed in 2006,, 19 June 2007."Warning shot for a cataclysm", CEA scientific news, Commissariat à l'énergie atomique et aux énergies alternatives, 14 June 2007. a scientific review on the enigmatic X-ray source Cygnus X-3 and its reported very high energy emission and the discovery of abnormal CNO abundances among accreting magnetic white dwarfs."Overabundance of nitrogen onto a magnetic white dwarf" , Paris-Meudon Observatory scientific news Paris Observatory, Mars 2003.
|
|
The reason for this shape may be a change in the black hole spin axis due to a minor merger, the presence of a binary black hole or due to interactions with the interstellar medium. Two radio sources with characteristics similar to accreting supermassive black holes have been observed in the centre of NGC 7674, at a projected separation of 0.35 parsec. NGC 7674 falls into the family of luminous infrared galaxies, with its infrared luminosity being 1011.54 . The luminous infrared galaxies are characterised by intense star forming activity.
|
|
But such views are not unchallenged since Cuyania is alternatively suggested to have drifted across Iapetus Ocean as a microcontinent starting in Laurentia and accreting then to Gondwana. Further a third model claims Cuyania is para- autochthonous and arrived at its current place by strike-slip fault movements starting not from Laurentia but from another region of Gondwana. The fact that Precordillera terrane has many trilobite genera in common with Laurentia but many species are endemic have led to some differing interpretations on what paleogeographic and tectonic history conditions are plausible explanations for this biogeography.
|
|
SWIFT J1756.9−2508 is a millisecond pulsar with a rotation frequency of 182 Hz (period of 5.5 ms). It was discovered in 2007 by the Swift Gamma-Ray Burst Explorer and found to have a companion with a mass between 0.0067 and 0.030 solar masses. It is thought that the companion is the remnant of a former companion star, now stripped down to a planetary-mass core. The pulsar is accreting mass from this companion, resulting in occasional violent outbursts from the accumulated material on the neutron star.
|
|
Rounded balls of tephra are called accretionary lapilli if they consist of layered volcanic ash particles. Accretionary lapilli are formed by a process of wet ash aggregation due to moisture in volcanic clouds that sticks the particles together, with the volcanic ash nucleating on some object and then accreting to it in layers before the accretionary lapillus falls from the cloud. Accretionary lapilli are like volcanic hailstones that form by the addition of concentric layers of moist ash around a central nucleus. This texture can be confused with spherulitic and axiolitic texture.
|
|
The matter streams from the donor into the accretor at the intersection of the two Roche Lobes, which is also the location of the first LaGrange point, or L1. Because of the rotation of the two stars around a common center of gravity, the material then forms a jet travelling towards the accretor. Because compact stars have high gravitational fields, the material falls with a high velocity and angular momentum towards the neutron star. However, the angular momentum prevents it from immediately joining the surface of the accreting star.
|
|
This binary star system consists of a red giant (Mira, designated Mira A) undergoing mass loss and a high temperature white dwarf companion (Mira B) that is accreting mass from the primary. Such an arrangement of stars is known as a symbiotic system and this is the closest such symbiotic pair to the Sun. Examination of this system by the Chandra X-ray Observatory shows a direct mass exchange along a bridge of matter from the primary to the white dwarf. The two stars are currently separated by about 70 astronomical units.
|
|
The light curve saw two maxima a few months after the outburst, along with strong oscillations. Today its brightness is visual magnitude 15.5. This is a close binary star system consisting of a white dwarf with 93% of the Sun's mass – the source for the nova explosion – and a lower mass red dwarf companion from which the white dwarf is accreting matter. The system is located approximately 4,500 light years from the Sun based on parallax, with its visual magnitude being diminished by an extinction of due to interstellar dust.
|
|
In finance, the term accretion refers to a positive change in value following a transaction; it is applied in several contexts. When trading in bonds, accretion is the capital gain expected when a bond is bought at a discount to its par value,Accretion definition on the financial dictionary given that it is expected to mature at par. Accretion can be thought of as the antonym of amortization: see here also, Accreting swap vs Amortising swap. In a corporate finance context, accretion is essentially the actual value created after a particular transaction.
|
|
The hierarchical triple star system consists of two B-type giant stars, the inner with spectral types B3III and the outer Be, as well as one unseen stellar-mass companion in the inner binary with an orbital period of 40.33 days. This unseen companion is inferred to be a non-accreting stellar-mass black hole of at least 4 . At a distance of approximately 1,120 light-years, QV Telescopii is, , the closest known black hole to Earth and the only known visible star system to contain a black hole.
|
|
Since it is difficult to fuel quasars for many billions of years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy. Radiation from quasars is partially "nonthermal" (i.e., not due to black-body radiation), and approximately 10% are observed to also have jets and lobes like those of radio galaxies that also carry significant (but poorly understood) amounts of energy in the form of particles moving at relativistic speeds. Extremely high energies might be explained by several mechanisms (see Fermi acceleration and Centrifugal mechanism of acceleration).
|
|
These are thought to be caused by the release of gravitational potential energy when part of the accretion disc collapses onto the star, rather than through a release of energy due to fusion. In general, binary systems with a white dwarf accreting matter from a stellar companion are called cataclysmic variables. As well as novae and dwarf novae, several other classes of these variables are known, including polars and intermediate polars, both of which feature highly magnetic white dwarfs. Both fusion- and accretion-powered cataclysmic variables have been observed to be X-ray sources.
|
|
As this stellar material accelerates in Scorpius X-1's gravitational field, X-rays are emitted. The measured luminosity for Scorpius X-1 is consistent with a neutron star which is accreting matter at its Eddington limit. This system is classified as a low-mass X-ray binary; the neutron star is roughly 1.4 solar masses, while the donor star is only 0.42 solar masses. The two stars were probably not born together; recent research suggests that the binary may have been formed by a close encounter inside a globular cluster.
|
|
Tor Bergeron (15 August 1891 – 13 June 1977) was a Swedish meteorologist who proposed a mechanism for the formation of precipitation in clouds. In the 1930s, Bergeron and W. Findeisen developed the concept that clouds contain both supercooled water and ice crystals. According to Bergeron, most precipitation is formed as a consequence of water evaporating from small supercooled droplets and accreting onto ice crystals, which then fall as snow, or melt and fall as cold rain depending on the ambient air temperature. This process is known as the Bergeron Process, and is believed to be the primary process by which precipitation is formed.
|
|
The X-ray continuum can arise from bremsstrahlung, black-body radiation, synchrotron radiation, or what is called inverse Compton scattering of lower-energy photons by relativistic electrons, knock-on collisions of fast protons with atomic electrons, and atomic recombination, with or without additional electron transitions. An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate mass star. Hercules X-1 is composed of a neutron star accreting matter from a normal star (HZ Herculis) probably due to Roche lobe overflow.
|
|
The Yakutat Block is a terrane in the process of accreting to the North American continent along the south central coast of Alaska. It has been displaced about 600 km northward since the Cenozoic along the Queen Charlotte- Fairweather fault system. The Yakutat Block is bounded on the northeast by the Fairweather Fault, and on the north by a system of thrust and possibly strike- slip faults in the Chugach Mountains and St. Elias Mountains. The Yakutat Block is bounded on its southwest side by an as yet undefined underwater geologic feature known as the Transition Zone.
|
|
Global Positioning System (GPS) measurements indicate that the Yakutat block has a distinctive velocity relative to both the Pacific Plate and the North American Plate. Thus it appears to be a terrane in the process of accreting rather than a block already sutured on to the Pacific or North American plate. Relative to North America, the Yakutat Block moves at a rate of about 45 mm/yr to the north northwest, along the Fairweather fault. There is about 20 mm/yr of contraction between the Yakutat block and the Pacific plate, which is probably accommodated on an offshore structure.
|
|
Microorganisms or capsules captured in the accretion disc can be captured along with the dust into asteroids. During aqueous alteration the asteroids contain water, inorganic salts and organics, and astroecology experiments with meteorites showed that algae, bacteria, fungi and plant cultures can grow in the asteroids in these media. Microorganisms can then spread in the accreting solar nebula, and will be delivered to planets in comets and in asteroids. The microorganisms can grow on nutrients in the carrier comets and asteroids in the aqueous planetary environments, until they adapt to the local environments and nutrients on the planets.
|
|
The Main Uralian Fault formed in the Riphean (early Neoproterozoic) in the breakup of the supercontinent Rodinia as a rift valley between the Baltica and the Angara Plate (Siberian craton). As these two plates pulled apart eventually a mid-ocean ridge formed. The ridge was of basic (basalt) and ultramafic material. Some 500 million years later, in the Silurian, a subduction zone formed on the western margin of the Angara Plate, which at the time was on the western edge of Gondwana, and the oceanic plate was subducted underneath the Angara Plate, accreting some of the basalts and ultramafics onto the Angara Plate.
|
|
Gas in the central part of the nebula, with relatively low angular momentum, undergoes fast compression and forms a hot hydrostatic (not contracting) core containing a small fraction of the mass of the original nebula. This core forms the seed of what will become a star. As the collapse continues, conservation of angular momentum means that the rotation of the infalling envelope accelerates, which largely prevents the gas from directly accreting onto the central core. The gas is instead forced to spread outwards near its equatorial plane, forming a disk, which in turn accretes onto the core.
|
|
The process of coastal change is still continuing, with the soft cliffs on some parts of the Solent, such as Fort Victoria, constantly eroding, whilst other parts, such as Ryde Sands, are accreting. The Solent is a comparatively shallow stretch of tidal water. It has an unusual double tide that is both favourable and hazardous to maritime activities with its strong tidal movements and quickly changing sea states. Coupled with the above, the Solent is renowned for its large volume of vessel usage, thus resulting in one of the highest density of declared lifeboat stations in the world.
|
|
It has been suggested that the coeval Famatinian orogeny in Western Gondwana (South America) is the "southward" continuation of the Taconic orogeny. This has been explained by adding that the continent Laurentia could have collided with Western Gondwana in early Paleozoic times due to the closure of the Iapetus Ocean. According to this view the Cuyania terrane would be an allochtonous block of Laurentian origin that was left in Gondwana. But such views are not unchallenged since Cuyania is alternatively suggested to have drifted across Iapetus Ocean as a microcontinent starting in Laurentia and accreting then to Gondwana.
|
|
In the core of the larger spiral structure of NGC 1300, the nucleus shows a "grand-design" spiral structure that is about 3,300 light- years long. Only galaxies with large-scale bars appear to have these grand- design inner disks — a spiral within a spiral. Models suggest that the gas in a bar can be funneled inwards, and then spiral into the center through the grand-design disk, where it can potentially fuel a central supermassive black hole (SMBH). NGC 1300 is not known to have an active nucleus, indicating that its central black hole is not accreting matter.
|
|
When it was discovered in 2003, during the quiescent phase, V455 Andromedae was classified as a cataclysmic variable, since its spectrum is similar to U Geminorum. V455 Andromedae is therefore a binary star where the primary is a white dwarf that is accreting matter from the secondary donor star. The rotation period of the white dwarf, slightly less than 68 seconds, is shorter than the orbital period so the white dwarf must possess a magnetic field channelling the material from the accretion disk to the poles of the white dwarf. This qualifies V455 Andromedae as a cataclysmic variable of the intermediate polar type.
|
|
Fusion of helium in the core of low mass stars. A helium flash is a very brief thermal runaway nuclear fusion of large quantities of helium into carbon through the triple-alpha process in the core of low mass stars (between 0.8 solar masses () and 2.0 ) during their red giant phase (the Sun is predicted to experience a flash 1.2 billion years after it leaves the main sequence). A much rarer runaway helium fusion process can also occur on the surface of accreting white dwarf stars. Low mass stars do not produce enough gravitational pressure to initiate normal helium fusion.
|
|
However, the current understanding of Earth's formation allows for less than 1% of Earth's material accreting after the Moon formed, implying that the material accreted later must have been very water-rich. Models of early Solar System dynamics have shown that icy asteroids could have been delivered to the inner Solar System (including Earth) during this period if Jupiter migrated closer to the Sun. Yet a third hypothesis, supported by evidence from molybdenum isotope ratios, suggests that the Earth gained most of its water from the same interplanetary collision that caused the formation of the Moon.
|
|
Analogous to the process leading to novae, degenerate matter can also accumulate on the surface of a neutron star that is accreting gas from a close companion. If a sufficiently thick layer of hydrogen accumulates, ignition of runaway hydrogen fusion can then lead to an X-ray burst. As with novae, such bursts tend to repeat and may also be triggered by helium or even carbon fusion. It has been proposed that in the case of "superbursts", runaway breakup of accumulated heavy nuclei into iron group nuclei via photodissociation rather than nuclear fusion could contribute the majority of the energy of the burst.
|
|
The generic term lavacicle has been applied to lava stalactites and stalagmites indiscriminately and evolved from the word icicle. Like limestone stalactites, they can leave lava drips on the floor that turn into lava stalagmites and may eventually fuse with the corresponding stalactite to form a column. Shark tooth stalactites The shark tooth stalactite is broad and tapering in appearance. It may begin as a small driblet of lava from a semi-solid ceiling, but then grows by accreting layers as successive flows of lava rise and fall in the lava tube, coating and recoating the stalactite with more material.
|
|
Planetesimals constitute the building blocks of both terrestrial and giant planets. Some of the moons of Jupiter, Saturn, and Uranus are believed to have formed from smaller, circumplanetary analogs of the protoplanetary disks. The formation of planets and moons in geometrically thin, gas- and dust-rich disks is the reason why the planets are arranged in an ecliptic plane. Tens of millions of years after the formation of the Solar System, the inner few AU of the Solar System likely contained dozens of moon- to Mars-sized bodies that were accreting and consolidating into the terrestrial planets that we now see.
|
|
Mass is accreting onto the star at the rate of about times the mass of the Sun per year. RU Lupi has an estimated mass of 0.6–0.7 times the mass of the Sun and 1.6 times the Sun's radius. It is radiating more than double the luminosity of the Sun, at an effective temperature of about 3,950 K. RU Lupi is surrounded by a circumstellar disk of dust that has a combined mass of up to 0.032 times the mass of the Sun. The particles in the disk vary in size, but range up to a centimeter in cross-section.
|
|
Modelling the formation of the terrestrial and gas giants is relatively straightforward and uncontroversial. The terrestrial planets of the Solar System are widely understood to have formed through collisional accumulation of planetesimals within the protoplanetary disc. The gas giants—Jupiter, Saturn, and their extrasolar counterpart planets—are thought to have formed solid cores of around 10 Earth masses () through the same process, while accreting gaseous envelopes from the surrounding solar nebula over the course of a few to several million years (Ma), although alternative models of core formation based on pebble accretion have recently been proposed. Some extrasolar giant planets may instead have formed via gravitational disk instabilities.
|
|
His 1962 book, Вселенная, жизнь, разум (Universe, Life, Intelligence), was expanded upon and reissued in 1966 with American astronomer Carl Sagan as co-author under the title Intelligent Life in the Universe (1966). This was the first comprehensive discussion of this field. Discussing the biological as well as astronomical issues of the subject, its unique format, alternating paragraphs written by Shklovsky and Sagan, demonstrated the deep mutual regard between the two and allowed them to express their views without compromise. In 1967, before the discovery of pulsars, Shklovsky examined the X-ray and optical observations of Scorpius X-1 and correctly concluded that the radiation comes from an accreting neutron star.
|
|
FO Aquarii is an intermediate polar star system in the constellation Aquarius. The white dwarf and companion star orbit each other with a period of approximately 4.85 hours. The system is famous for a very strong optical pulsation which occurs every 20.9 minutes, corresponding with the rotational period of the accreting white dwarf. Prior to 2016, the system's long-term optical brightness varied between apparent magnitude 12.7 and 14.2, but in early 2016, it faded to magnitude 15.8 and thereafter began a slow recovery to its normal brightness, behavior which is indicative of a temporary dropoff in the mass-transfer rate between the two stars.
|
|
The stellar birthline is a predicted line on the Hertzsprung–Russell diagram that relates the effective temperature and luminosity of pre-main-sequence stars at the start of their contraction. Prior to this point, the objects are accreting protostars, and are so deeply embedded in the cloud of dust and gas from which they are forming that they radiate only in far infrared and millimeter wavelengths. Once stellar winds disperse this cloud, the star becomes visible as a pre-main-sequence object. The set of locations on the Hertzsprung–Russell diagram where these newly visible stars reside is called the birthline, and is found above the main sequence.
|
|
The brown dwarf is known to have survived being engulfed when the primary star was a red giant, because it was relatively massive. At that time, the red giant had a radius of . It is thought that the red giant phase of the current white dwarf was shortened from around 100 million years on average, to a few decades—while the brown dwarf was within the red giant, it hastened the expulsion of matter during this phase by rapidly heating gas and accreting a portion of it. During this phase, drag from the red giant also decreased the orbital speed of the brown dwarf, causing it to fall inwards.
|
|
Dong Lai, Francois Foucart, Douglas N. C. Lin, "Evolution of Spin Direction of Accreting Magnetic Protostars and Spin-Orbit Misalignment in Exoplanetary Systems" The accretion disk of the protostar IRAS 16293-2422 has parts rotating in opposite directions. This is the first known example of a counterrotating accretion disk. If this system forms planets, the inner planets will likely orbit in the opposite direction to the outer planets."Still-Forming Solar System May Have Planets Orbiting Star in Opposite Directions, Astronomers Say", National Radio Astronomy Observatory, February 13, 2006 WASP-17b was the first exoplanet that was discovered to be orbiting its star opposite to the direction the star is rotating.
|
|
Due to the youth of RCW 36, most of the stars in the cluster are at an early stage of stellar evolution where they are known as young stellar objects or pre-main-sequence stars. These stars are still in the process of contraction before they reach the main sequence, and they may still have gas accreting onto them from either a circumstellar disk or envelope. Cluster members in RCW 36 have been identified through both infrared and X-ray observations. Bright infrared sources, attributed to massive stars, were first identified by the TIFR 100-cm balloon-born telescope from the National Balloon Facility in Hyderabad, India.
|
|
The Markarian 231 galaxy is now undergoing an energetic starburst. A nuclear ring of active star formation has been found in the center with a rate of formation greater than 100 solar masses per year. It is one of the most ultraluminous infrared galaxies with power derived from an accreting black hole in the center, and the closest known quasar. A 2015 study suggested that the central black hole, estimated to be 150 million times the mass of our Sun, may have a black hole companion weighing in at 4 million solar masses, and that the duo completed an orbit around each other every 1.2 years.
|
|
The Dyfi is a classic bar-built estuary, and one of the foremost examples of a drying, sandy, nutrient-poor estuary. Important populations of migratory fish, birds and otter occur along with extensive areas of saltmarsh (Atlantic salt meadow). The spit dune system of Ynyslas is an actively accreting system with good representation of dune community succession including marram fore-dunes and humid dune slacks. The estuarine raised mire of Cors fochno is one of the largest and best preserved active raised bogs in the UK. It is a key site for climate-related research and supports important assemblages of lower plants, invertebrates and birds.
|
|
Since the early 1990s, physicists have thought that technology has evolved to the point where detection of gravitational waves—of significant astrophysical interest—is now possible. In August 2002, LIGO began its search for cosmic gravitational waves. Measurable emissions of gravitational waves are expected from binary systems (collisions and coalescences of neutron stars or black holes), supernova explosions of massive stars (which form neutron stars and black holes), accreting neutron stars, rotations of neutron stars with deformed crusts, and the remnants of gravitational radiation created by the birth of the universe. The observatory may, in theory, also observe more exotic hypothetical phenomena, such as gravitational waves caused by oscillating cosmic strings or colliding domain walls.
|
|
Accessed on line July 8, 2008. If the combined mass is not above the Chandrasekhar limit but is larger than the minimum mass to fuse carbon (about ), a carbon star could be produced, with a lifetime of around (1 million) years. Also, if two helium white dwarfs with a combined mass of at least collide, a helium star may be produced, with a lifetime of a few hundred million years. Finally brown dwarfs can form new stars colliding with each other to form a red dwarf star, that can survive for (10 trillion) years, or accreting gas at very slow rates from the remaining interstellar medium until they have enough mass to start hydrogen burning as red dwarfs too.
|
|
The surface of the neutron star is very hot, with temperatures exceeding 109 K: hotter than the cores of all but the most massive stars. This heat is dominated either by nuclear fusion in the accreting gas or by compression of the gas by the neutron star's gravity. Because of the high temperature, unusual nuclear processes may take place as the envelope of the red giant falls onto the neutron star's surface. Hydrogen may fuse to produce a different mixture of isotopes than it does in ordinary stellar nucleosynthesis, and some astronomers have proposed that the rapid proton nucleosynthesis that occurs in X-ray bursts also takes place inside Thorne–Żytkow objects.
|
|
There exists a class of 'radiatively inefficient' solutions to the equations that govern accretion. The most widely known of these is the Advection Dominated Accretion Flow (ADAF), but other theories exist. In this type of accretion, which is important for accretion rates well below the Eddington limit, the accreting matter does not form a thin disc and consequently does not efficiently radiate away the energy that it acquired as it moved close to the black hole. Radiatively inefficient accretion has been used to explain the lack of strong AGN-type radiation from massive black holes at the centres of elliptical galaxies in clusters, where otherwise we might expect high accretion rates and correspondingly high luminosities.
|
|
However, Hippocamp only accounts for two percent of the missing volume of material generated by the Pharos impact event, and the reason for the absence of the rest of the debris remains unknown. As with the other small inner moons of Neptune, Hippocamp is thought to have been repeatedly disrupted by comet impacts after it had coalesced from debris ejected from Proteus. Based on the formation rate of large craters on Proteus, Hippocamp is estimated to have been disrupted about nine times in the past 4 billion years, re-accreting back after each disruption event. These disruption events substantially reduce the moon's orbital eccentricity and inclination, providing an explanation for Hippocamp's present circular orbit despite its proximity to Proteus.
|
|
As it continues to flow and begins to rise up the adverse slope beneath temperate (or "warm- based") glaciers, the pressure decreases and frazil ice accretes in the basal ice. The sediment load carried by the water will be entrained in the accreted ice.The evidence for this includes elevated concentrations of atmospheric weapon testing-produced tritium in the basal ice of several glaciers (signifying young ice) and the observation of rapid growth of ice crystals around water discharge vents at glacier termini. At the point in the glacier where the ice is accreting on the adverse slope near the glacier terminus, ablation of the upper surface ice exceeds (for recently observed glaciers) the rate of accretion at the bottom.
|
|
It continues to orbit the accretor in the plane of the orbital axis, colliding with other accreting material en route, thereby losing energy, and in so doing forming an accretion disk, which also lies on the plane of the orbital axis. In an X-ray burster, this material accretes onto the surface of the neutron star, where it forms a dense layer. After mere hours of accumulation and gravitational compression, nuclear fusion starts in this matter. This begins as a stable process, the hot CNO cycle, however, continued accretion causes a degenerate shell of matter, in which the temperature rises (greater than 1 × 109 kelvin) but this does not alleviate thermodynamic conditions.
|
|
The stream of stars was discovered in the early 21st century by astronomers conducting the Sloan Digital Sky Survey. It was in the course of investigating this ring of stars, and a closely spaced group of globular clusters similar to those associated with the Sagittarius Dwarf Elliptical Galaxy, that the Canis Major Dwarf Galaxy was discovered. Globular clusters thought to be associated with the Canis Major Dwarf galaxy include NGC 1851, NGC 1904, NGC 2298 and NGC 2808, all of which may have been part of the galaxy's globular cluster system before accreting into the Milky Way. NGC 1261 is another nearby cluster, but its velocity differs enough to make its relationship to the system unclear.
|
|
The EG Andromedae system hosts a white dwarf and an evolved giant star, with an orbital period of 482 days and a half. The giant star is losing mass through its stellar wind at a rate higher than 10−6 /yr, and the white dwarf is accreting a fraction of this mass without forming an accretion disk. The white dwarf itself could emit a hot wind that interacts with the cooler one of the giant star, in addition to inducing the photoionization of the latter. X-ray observations, however, failed to detect emission coming from colliding winds, but established the non-magnetic nature of the white dwarf and estimated its accretion rate at 1-10 /yr.
|
|
Gamma Cassiopeiae is the prototype of a small group of stellar sources of X-ray radiation that is about 10 times stronger than emitted from other B or Be stars. The character of the X-ray spectrum is Be thermal, possibly emitted from plasmas of temperatures up to least ten million kelvins, and shows very short term and long-term cycles. Historically, it has been held that these X-rays might be excited by matter originating from the star, from a hot wind or a disk around the star, accreting onto the surface of a degenerate companion, such as a white dwarf or neutron star. However, there are difficulties with either of these hypotheses.
|
|
There are a growing number of recurrent X-ray transients, characterized by short outbursts with very fast rise times (~ tens of minutes) and typical durations of a few hours that are associated with OB supergiants and hence define a new class of massive X-ray binaries: Supergiant Fast X-ray Transients (SFXTs). XTE J1739–302 is one of these. Discovered in 1997, remaining active only one day, with an X-ray spectrum well fitted with a thermal bremsstrahlung (temperature of ∼20 keV), resembling the spectral properties of accreting pulsars, it was at first classified as a peculiar Be/X-ray transient with an unusually short outburst. A new burst was observed on Apr 8 2008 with Swift.
|
|
The sand couch-grass Elytrigia juncea also performs this function on the seaward edge of the dunes, and is responsible, with some other pioneers like the sea rocket Cakile maritima, for initiating the process of dune building by trapping wind blown sand. In accreting situations small mounds of vegetation or tide-washed debris form and tend to enlarge as the wind-speed drops in the lee of the mound, allowing blowing sand (picked up from the off-shore banks) to fall out of the air stream. The pioneering plants are physiologically adapted to withstand the problems of high salt contents in the air and soil, and are good examples of stress tolerators, as well as having some ruderal characteristics.
|
|
There are a growing number of recurrent X-ray transients, characterized by short outbursts with very fast rise times (tens of minutes) and typical durations of a few hours that are associated with OB supergiants and hence define a new class of massive X-ray binaries: Supergiant Fast X-ray Transients (SFXTs). XTE J1739–302 is one of these. Discovered in 1997, remaining active only one day, with an X-ray spectrum well fitted with a thermal bremsstrahlung (temperature of ∼20 keV), resembling the spectral properties of accreting pulsars, it was at first classified as a peculiar Be/X-ray transient with an unusually short outburst. A new burst was observed on 8 April 2008 with Swift.
|
|
GRO J1655-40 is a binary star consisting of an evolved F-type primary star and a massive, unseen companion, which orbit each other once every 2.6 days in the constellation of Scorpius. Gas from the surface of the visible star is accreted onto the dark companion, which appears to be a stellar black hole with several times the mass of the Sun. The optical companion of this low-mass X-ray binary is a subgiant F star. Along with GRS 1915+105, GRO J1655-40 is one of at least two galactic "microquasars" that may provide a link between the supermassive black holes generally believed to power extragalactic quasars and more local accreting black hole systems.
|
|
The Gonâve Microplate began to form in the Early Eocene after the northern part of the leading edge of the Caribbean Plate (present day Cuba) collided with the Bahamas platform. This part of the plate was unable to move further to the east and a transform fault system developed to the south, effectively cutting off this northern area and accreting it to the North American Plate. A large left-stepping offset formed along this zone just east of the Yucatán peninsula creating a pull-apart basin, which continued to extend until the onset of seafloor spreading, creating the Cayman spreading centre. Further movement on this fault system created the Cayman Trough, although at that time the future microplate was still firmly attached to the Caribbean Plate.
|
|
Eta Chamaeleontis is the brightest and most massive member of the eponymous Eta Chamaeleontis cluster (also known as the Eta Chamaeleontis association or Mamajek 1, pronounced ), a very nearby (316 light years), and young (8 million years old) stellar moving group discovered in 1999. The cluster contains nearly 20 stellar members spread out over a 40-arcminute diameter region of sky, including the neighboring A-type star HD 75505 and the eclipsing binary RS Cha. The eclipsing binary RS Cha is a well-constrained system which enables precise age-dating, which recent results yield an age of 9 million years. All of the low-mass members (including RS Cha) are pre-main sequence, and several of them appear to still be accreting from protoplanetary disks.
|
|
Interest in the MRI is based on the fact that it appears to give an explanation for the origin of turbulent flow in astrophysical accretion disks (Balbus and Hawley, 1991). A promising model for the compact, intense X-ray sources discovered in the 1960s was that of a neutron star or black hole drawing in (“accreting”) gas from its surroundings (Prendergast and Burbidge, 1968). Such gas always accretes with a finite amount of angular momentum relative to the central object, and so it must first form a rotating disk — it cannot accrete directly onto the object without first losing its angular momentum. But how an element of gaseous fluid managed to lose its angular momentum and spiral onto the central object was not at all obvious.
|
|
In his original model Krzemiński interpreted the observed changes in the light curve as a consequence of the uneven luminous surface of a white dwarf. Soon, however, it turned out that in the case of U Geminorum it is not a white dwarf that is obscured. Correct model of the system was introduced by Józef Smak, which is for a binary system containing a white dwarf and filling Roche surface of star in main sequence, made the accretion disc and the so-called "hot spot" that is the place where accreting matter collides with the disc. It is the emergence of "hot spots" behind the disc and its eclipse by the secondary component that was responsible for the unusual appearance of the light curve of U Geminorum.
|
|
It has been proposed that gas giants orbiting red giants at distances similar to that of Jupiter could be hot Jupiters due to the intense irradiation they would receive from their stars. It is very likely that in the Solar System Jupiter will become a hot Jupiter after the transformation of the Sun into a red giant. The recent discovery of particularly low density gas giants orbiting red giant stars supports this theory. Hot Jupiters orbiting red giants would differ from those orbiting main-sequence stars in a number of ways, most notably the possibility of accreting material from the stellar winds of their stars and, assuming a fast rotation (not tidally locked to their stars), a much more evenly distributed heat with many narrow-banded jets.
|
|
Typically, accreting terranes are portions of continental crust which have rifted off another continental mass and been transported surrounded by oceanic crust, or they are old island arcs formed at some distant subduction zone. A tectonostratigraphic terrane is a fault-bounded package of rocks of at least regional extent characterized by a geologic history which differs from that of neighboring terranes. The basic characteristics of these terranes is that the present spatial relations are not compatible with the inferred geologic histories. Where terranes which lie next to each other possess strata of the same age, it must be demonstrable that the geologic evolutions are different and incompatible, and there must be an absence of intermediate lithofacies which could link the strata.
|
|
A Peter Pan disk is a circumstellar disk around a star or brown dwarf that appears to have retained enough gas to form a gas giant planet for much longer than the typically assumed gas dispersal timescale of approximately 5 million years. Several examples of such disks have been observed to orbit stars with spectral types of M or later. The presence of gas around these disks has generally been inferred from the total amount of radiation emitted from the disk at infrared wavelengths, and/or spectroscopic signatures of hydrogen accreting onto the star. To fit one specific definition of a Peter Pan disk, the source needs to have an infrared "color" of Ks-W4>2, an age of >20 Myr and spectroscopic evidence of accretion.
|
|
A transient X-ray source first discovered in 1996 by the Italian-Dutch BeppoSAX satellite, SAX J1808.4−3658 revealed X-ray pulsations at the 401 Hz neutron star spin frequency when it was observed during a subsequent outburst in 1998 by NASA's RXTE satellite. The neutron star is orbited by a brown dwarf binary companion with a likely mass of 0.05 solar masses, every 2.01 hours. X-ray burst oscillations and quasi-periodic oscillations in addition to coherent X-ray pulsations have been seen from SAX J1808.4-3658, making it a Rosetta stone for interpretation of the timing behavior of low-mass X-ray binaries. These accreting millisecond X-ray pulsars are thought to be the evolutionary progenitors of recycled radio millisecond pulsars.
|
|
Gravitation from supermassive black holes in the center of many galaxies is thought to power active objects such as Seyfert galaxies and quasars, and the relationship between the mass of the central black hole and the mass of the host galaxy depends upon the galaxy type. An active galactic nucleus (AGN) is now considered to be a galactic core hosting a massive black hole that is accreting matter and displays a sufficiently strong luminosity. The nuclear region of the Milky Way, for example, lacks sufficient luminosity to satisfy this condition. The unified model of AGN is the concept that the large range of observed properties of the AGN taxonomy can be explained using just a small number of physical parameters.
|
|
When protecting the coastline it is important to understand the how the sedimentary budget can be affected when implementing appropriate coastal protecting techniques. Often management plans for coastal erosion have seen the use of ‘hard’ engineering structures as a means of protecting the coastline from recession. In particular groynes which are used to trap the longshore drift of sediment that often deprives a beach. Groynes have the ability to change the coast's sediment budget, accreting up drift beaches but at the same time starving down drift beaches. This management approach is not used so much these days, with modern knowledge of coastal dynamics promoting the use of ‘soft’, natural approaches such as nourishment and preservation of natural systems such as dunes.
|
|
Artist's impression of the circumstellar disk surrounding GG Tauri A and B T Tauri stars are usually surrounded by circumstellar disks. These disks coalesce into protoplanets and then into planets. The inner disk around GG Tauri has a mass of about , or about the mass of Jupiter, at a temperature of about 20 to 30 K. However, because mass is currently accreting into the stars themselves, the inner disk must have been consumed, or another larger, circumstellar disk must have been supplying mass into the smaller disk. A search for diatomic hydrogen gas near GG Tauri was conducted; H2 gas could be found up to 100 AU away from the center of the system, with significant emission also being detected 30 AU away.
|
|
Modelling has hypothesised that material in orbit around the Earth may have accreted to form the Moon in three consecutive phases; accreting first from the bodies initially present outside the Earth's Roche limit, which acted to confine the inner disk material within the Roche limit. The inner disk slowly and viscously spread back out to the Earth's Roche limit, pushing along outer bodies via resonant interactions. After several tens of years, the disk spread beyond the Roche limit, and started producing new objects that continued the growth of the Moon, until the inner disk was depleted in mass after several hundreds of years. Material in stable Kepler orbits was thus likely to hit the earth-moon system sometime later (because the Earth-Moon system's Kepler orbit around the sun also remains stable).
|
|
Map of the Leeward Antilles La Tortuga Island, Federal Dependencies of Venezuela The Leeward Antilles () are a chain of islands in the Caribbean – specifically, the southerly islands of the Lesser Antilles (and, in turn, the Antilles and the West Indies) along the southeastern fringe of the Caribbean Sea, just north of the Venezuelan coast of the South American mainland. The Leeward Antilles, while among the Lesser Antilles, are not to be confused with the Leeward Islands (also of the Lesser Antilles) to the northeast. Largely lacking in volcanic activity, the Leeward Antilles island arc occurs along the deformed southern edge of the Caribbean Plate and was formed by the plate's subduction under the South American Plate. Recent studies indicate that the Leeward Antilles are accreting to South America.
|
|
Swan Island's natural vegetation includes areas of coastal scrub, relict patches of coastal woodland and extensive areas of saltmarsh. The island is part of the Swan Bay and Port Phillip Bay Islands Important Bird Area, identified as such by BirdLife International because of its importance for orange-bellied parrots, waders and seabirds. It is ornithologically notable for the critically endangered orange-bellied parrot, for which the saltmarsh serves as one of its few regular wintering sites. Sand Island contains saltmarsh-fringed lagoons bordered in the east by colonising shrubs and grasses on newly formed dunes; its accreting eastern beach, now connected to Swan Island, forms an important high tide roosting area for the migratory waders that feed on the Swan Bay mudflats at low tide, while the lagoons are much used by black swans and other waterbirds.
|
|
Chandra X-ray spectrum of Cygnus X-1 showing a characteristic peak near due to ionized iron in the accretion disk, but the peak is gravitationally red-shifted, broadened by the Doppler effect, and skewed toward lower energies The compact object is thought to be orbited by a thin, flat disk of accreting matter known as an accretion disk. This disk is intensely heated by friction between ionized gas in faster-moving inner orbits and that in slower outer ones. It is divided into a hot inner region with a relatively high level of ionization—forming a plasma—and a cooler, less ionized outer region that extends to an estimated 500 times the Schwarzschild radius, or about 15,000 km. Though highly and erratically variable, Cygnus X-1 is typically the brightest persistent source of hard X-rays—those with energies from about 30 up to several hundred keV—in the sky.
|
|
X-ray bursters are one class of X-ray binary stars exhibiting periodic and rapid increases in luminosity (typically a factor of 10 or greater) peaked in the X-ray regime of the electromagnetic spectrum. These astrophysical systems are composed of an accreting compact object, typically a neutron star or occasionally a black hole, and a companion 'donor' star; the mass of the donor star is used to categorize the system as either a high mass (above 10 solar masses) or low mass (less than 1 solar mass) X-ray binary, abbreviated as LMXB and HMXB, respectively. X-ray bursters differ observationally from other X-ray transient sources (such as X-ray pulsars and soft X-ray transients), showing a sharp rise time (1 – 10 seconds) followed by spectral softening (a property of cooling black bodies). Individual bursts are characterized by an integrated flux of 1039-40 ergs.
|
|
If Wd1 formed stars with a typical initial mass function then the cluster would have originally contained a significant number of very massive stars, such as those currently observed in the younger Arches cluster. Current estimates of the age of Wd1 are greater than the lifetimes of these stars, and stellar evolution models suggest that there would already have been 50–150 supernovae in Wd1, with a supernova rate of approximately one per 10,000 years over the last million years. However, to date only one definitive supernova remnant has been detected—the Westerlund 1 magnetar—and the lack of other compact objects and high-mass X-ray binaries is puzzling. A number of suggestions have been put forward, including high supernova kick velocities that disrupt binary systems, the formation of slowly accreting (and therefore undetectable) stellar mass black holes, or binary systems in which both objects are now compact objects, but the problem has yet to be resolved.
|
|
An artist's depiction of the orbits of the HR 6819 hierarchical triple star system, including the black hole Ab (red orbit) in the inner binary HR 6819 is a hierarchical triple containing a classical Be star in a wide orbit of unknown period around an inner 40.3 day binary, a B3 III star and a non-emitting (non-accreting) black hole (≥ ), designated Ab. Although the HR 6819 system has been described as a member of the Sco OB2 association of co-moving stars, a more recent analysis indicates it is an older system and not part of the association. The spectrum of HR 6819 contains both narrow and broadened lines. The broad lines originate from the rapidly-rotating Be star, while the narrow lines are from a more slowly-rotating B-class giant. The radial velocity variations of the lines indicate that the normal B giant is in a 40-day orbit, but not with the Be star.
|
|
This means that it is possible that most galaxies, including the Milky Way, have gone through an active stage, appearing as a quasar or some other class of active galaxy that depended on the black-hole mass and the accretion rate, and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation. Quasars in interacting galaxies The matter accreting onto the black hole is unlikely to fall directly in, but will have some angular momentum around the black hole, which will cause the matter to collect into an accretion disc. Quasars may also be ignited or re-ignited when normal galaxies merge and the black hole is infused with a fresh source of matter. In fact, it has been suggested that a quasar could form when the Andromeda Galaxy collides with our own Milky Way galaxy in approximately 3–5 billion years.
|
|
The Gonâve Microplate, showing location of the main fault zones The Septentrional-Orient fault zone (SOFZ) is a system of active coaxial left lateral-moving strike slip faults that runs along the northern side of the island of Hispaniola where Haiti and the Dominican Republic are located and continues along the south of Cuba along the northern margin of the Cayman Trough. The SOFZ shares approximately half of the relative motion between the North American and Caribbean tectonic plates with the Enriquillo-Plantain Garden fault zone and Walton fault zone which run along the southern side of Hispaniola and aong the southern margin of the Cayman Trough. Both fault zones terminate at the Mid-Cayman Rise to the west. Some researchers believe that the Enriquillo-Plantain Garden fault zone and the SOFZ bound a microplate, dubbed the Gonâve Microplate, a area of the northern Caribbean Plate that is in the process of shearing off the Caribbean Plate and accreting to the North America Plate.
|
|
This makes it unlikely that planetary embryos compositionally similar to carbonaceous chondrites supplied water to Earth # Earth's atmospheric content of Ne is significantly higher than would be expected had all the rare gases and H2O been accreted from planetary embryos with carbonaceous chondritic compositions. An alternative to the cometary and asteroidal delivery of H2O would be the accretion via physisorption during the formation of the terrestrial planets in the solar nebula. This would be consistent with the thermodynamic estimate of around two Earth masses of water vapor within 3AU of the solar accretionary disk, which would exceed by a factor of 40 the mass of water needed to accrete the equivalent of 50 Earth hydrospheres (the most extreme estimate of Earth's bulk H2O content) per terrestrial planet. Even though much of the nebular H2O(g) may be lost due to the high temperature environment of the accretionary disk, it is possible for physisorption of H2O on accreting grains to retain nearly three Earth hydrospheres of H2O at temperatures.
|
|
Rising sea levels and more intense sea storms from the 13th century onward very likely eroded these islands, increasingly exposing the Skegness coast to the tides.Museum of London Archaeology Service (2010). Records from the Middle Ages show that local people maintained sand banks as a form of sea defence; fines were levied for grazing animals on the dunes, which could weaken the defences. Skegness was flooded in 1525 or 1526 and loss of land continued during the century. A clay embankment, Roman Bank, was built in the late 16th century and was followed in c. 1670 by another closer to the sea (Green Bank) running from what is now North Shore Road to Cow Bank, following a line from St Andrew's Drive to Drummond Road.Kime (1986), pp. 34, 83–85. By the late 19th century, sands were accreting at Skegness; the retaining sea wall erected in 1878 was designed to support the resort town's seafront development rather than to protect it from the sea.Robinson (1989), pp. 156–157.
|
|