Are there black holes near the galactic nucleus?
Sombrero Galaxy
The nucleus of the Sombrero galaxy is classified as a low ionization nuclear emission region (LINER). These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain supermassive black holes). Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.
Active galactic nucleus
The enormous luminosities of these quasars as well as their unusual spectral properties indicated that their power source could not be ordinary stars. Accretion of gas onto a supermassive black hole was suggested as the source of quasars' power in papers by Edwin Salpeter and Yakov Zel'Dovich in 1964. In 1969 Donald Lynden-Bell proposed that nearby galaxies contain supermassive black holes at their centers as relics of "dead" quasars, and that black hole accretion was the power source for the non-stellar emission in nearby Seyfert galaxies. In the 1960s and 1970s, early X-ray astronomy observations demonstrated that Seyfert galaxies and quasars are powerful sources of X-ray emission, which originates from the inner regions of black hole accretion disks.
Black hole
By their very nature, black holes do not directly emit any electromagnetic radiation other than the hypothetical Hawking radiation, so astrophysicists searching for black holes must generally rely on indirect observations. For example, a black hole's existence can sometimes be inferred by observing its gravitational interactions with its surroundings.
Fuzzball (string theory)
Due to the mass-density inverse-square rule, all fuzzballs need not have unimaginable densities. There are also supermassive black holes, which are found at the center of virtually all galaxies. Sagittarius A*, the black hole at the center of our Milky Way galaxy, is 4.3 million . If fuzzball theory is correct, it has a mean density that is “only” 51 times that of gold.
Centaurus
One of the closest active galaxies to Earth is the Centaurus A galaxy, NGC 5128, at a distance of 11 million light-years (redshift 0.00183). It has a supermassive black hole at its core, which expels massive jets of matter that emit radio waves due to synchrotron radiation. Astronomers posit that its dust lanes, not common in elliptical galaxies, are due to a previous merger with another galaxy, probably a spiral galaxy. NGC 5128 appears in the optical spectrum as a fairly large elliptical galaxy with a prominent dust lane. Its overall magnitude is 7.0 and it has been seen under perfect conditions with the naked eye, making it one of the most distant objects visible to the unaided observer. In equatorial and southern latitudes, it is easily found by star hopping from Omega Centauri. In small telescopes, the dust lane is not visible; it begins to appear with about 4 inches of aperture under good conditions. In large amateur instruments, above about 12 inches in aperture, the dust lane's west-northwest to east-southeast direction is easily discerned. Another dim dust lane on the east side of the 12-arcminute-by-15-arcminute galaxy is also visible. ESO 270-17, also called the Fourcade-Figueroa Object, is a low-surface brightness object believed to be the remnants of a galaxy; it does not have a core and is very difficult to observe with an amateur telescope. It measures 7 arcminutes by 1 arcminute. It likely originated as a spiral galaxy and underwent a catastrophic gravitational interaction with Centaurus A around 500 million years ago, stopping its rotation and destroying its structure.
Peculiar galaxy
Scientists hypothesize that many peculiar galaxies are formed by the collision of two or more galaxies. As such, peculiar galaxies tend to host more active galactic nuclei than normal galaxies, indicating that they contain supermassive black holes. Many peculiar galaxies experience starbursts, or episodes of rapid star formation, due to the galaxies merging. The periods of elevated star formation and the luminosity resulting from active galactic nuclei cause peculiar galaxies to be slightly bluer in color than other galaxies.
Supermassive black hole
Arthur M. Wolfe and Geoffrey Burbidge noted in 1970 that the large velocity dispersion of the stars in the nuclear region of elliptical galaxies could only be explained by a large mass concentration at the nucleus; larger than could be explained by ordinary stars. They showed that the behavior could be explained by a massive black hole with up to 10 , or a large number of smaller black holes with masses below 10 . Dynamical evidence for a massive dark object was found at the core of the active elliptical galaxy Messier 87 in 1978, initially estimated at . Discovery of similar behavior in other galaxies soon followed, including the Andromeda Galaxy in 1984 and the Sombrero Galaxy in 1988.
Nuclear star cluster
NSCs are the central massive objects of fainter, low-mass galaxies where supermassive black holes (SMBHs) are not present or are of negligible mass. In the most massive galaxies, NSCs are entirely absent. Some galaxies, including the Milky Way, are known to contain both a NSC and a SMBH of comparable mass.
Messier 63
M63 is an active galaxy with a LINER nucleus. This displays as an unresolved nuclear source wrapped in a diffuse emission. The latter is extended along a position angle of 110° and soft X-rays and H-alpha emission can be observed coming from along nearly the same direction. The existence of a super massive black hole (SMBH) at the nucleus is uncertain; if it does exist, then the mass is estimated as .
NGC 3115
In 2011, NASA's Chandra X-ray Observatory examined the black hole at the center of the large galaxy. A flow of hot gas toward the supermassive black hole has been imaged, making this the first time clear evidence for such a flow has been observed in any black hole. As gas flows toward the black hole, it becomes hotter and brighter.
The researchers found the rise in gas temperature begins at about 700 light years from the black hole, giving the location of the Bondi radius. This suggests that the black hole in the center of NGC 3115 has a mass of about two billion , supporting previous results from optical observations. This would make NGC 3115 the nearest billion-solar-mass black hole to Earth.
Supermassive black hole
The nearby Andromeda Galaxy, 2.5 million light-years away, contains a central black hole, significantly larger than the Milky Way's. The largest supermassive black hole in the Milky Way's vicinity appears to be that of M87, at a mass of at a distance of 53.5 million light-years. The supergiant elliptical galaxy NGC 4889, at a distance of 336 million light-years away in the Coma Berenices constellation, contains a black hole measured to be .
NGC 5033
NGC 5033 contains a Seyfert nucleus, a type of active galactic nucleus. Like many other active galactic nuclei, this galaxy's nucleus is thought to contain a supermassive black hole. The bright emission seen in visible light (as well as other wavebands) is partially produced by the hot gas in the environment around this black hole.
PSR J0737-3039
A pulsar has recently been detected very near the super-massive black hole at the core of our galaxy, but its motion has not yet been officially confirmed as a capture orbit of Sgr A*. A pulsar-black hole system could be an even stronger test of Einstein's theory of general relativity, due to the immense gravitational forces exerted by both celestial objects. The Square Kilometre Array, a planned radio telescope due to be constructed in the southern hemisphere in 2018 (first light in 2020), will observe binary pulsar systems. It will also search for pulsar-black hole systems in order to test general relativity.
S5 0014+81
In 2009, a team of astronomers using the Swift spacecraft used the luminosity output of S5 0014+81 to measure the mass of the central black hole. To their surprise, they found out that the central black hole of S5 0014+81 is actually 10,000 times more massive than the black hole at the center of our galaxy, or equivalent to 40 billion solar masses. This makes it one of the most massive black holes ever discovered, more than six times the value of the black hole of Messier 87, which was thought to be the largest black hole for almost 60 years, and was coined to be an "ultramassive" black hole.
The Schwarzschild radius of this black hole is 118.35 billion kilometers, giving a diameter of 236.7 billion kilometers, 1,600 astronomical units, or about 40 times the radius of Pluto's orbit, and has a mass equivalent to four Large Magellanic Clouds. What is even more remarkable is that such a large black hole existed so early in the universe, at only 1.6 billion years after the Big Bang. This suggests that supermassive black holes formed very quickly.
Accretion disk
The most spectacular accretion disks found in nature are those of active galactic nuclei and of quasars, which are thought to be massive black holes at the center of galaxies. As matter enters the accretion disc, it follows a trajectory called a tendex line, which describes an inward spiral. This is because particles rub and bounce against each other in a turbulent flow, causing frictional heating which radiates energy away, reducing the particles' angular momentum, allowing the particle to drift inwards, driving the inward spiral. The loss of angular momentum manifests as a reduction in velocity; at a slower velocity, the particle wants to adopt a lower orbit. As the particle falls to this lower orbit, a portion of its gravitational potential energy is converted to increased velocity and the particle gains speed. Thus, the particle has lost energy even though it is now travelling faster than before; however, it has lost angular momentum. As a particle orbits closer and closer, its velocity increases, as velocity increases frictional heating increases as more and more of the particle's potential energy (relative to the black hole) is radiated away; the accretion disk of a black hole is hot enough to emit X-rays just outside the event horizon. The large luminosity of quasars is believed to be a result of gas being accreted by supermassive black holes. Elliptical accretion disks formed at tidal disruption of stars can be typical in galactic nuclei and quasars. Accretion process can convert about 10 percent to over 40 percent of the mass of an object into energy as compared to around 0.7 percent for nuclear fusion processes. In close binary systems the more massive primary component evolves faster and has already become a white dwarf, a neutron star, or a black hole, when the less massive companion reaches the giant state and exceeds its Roche lobe. A gas flow then develops from the companion star to the primary. Angular momentum conservation prevents a straight flow from one star to the other and an accretion disk forms instead.
Cygnus X-1
With further observations strengthening the evidence, by the end of 1973 the astronomical community generally conceded that Cygnus X-1 was most likely a black hole. More precise measurements of Cygnus X-1 demonstrated variability down to a single millisecond. This interval is consistent with turbulence in a disk of accreted matter surrounding a black hole—the accretion disk. X-ray bursts that last for about a third of a second match the expected time frame of matter falling toward a black hole.
Cygnus X-1 has since been studied extensively using observations by orbiting and ground-based instruments. The similarities between the emissions of X-ray binaries such as HDE 226868/Cygnus X-1 and active galactic nuclei suggests a common mechanism of energy generation involving a black hole, an orbiting accretion disk and associated jets. For this reason, Cygnus X-1 is identified among a class of objects called microquasars; an analog of the quasars, or quasi-stellar radio sources, now known to be distant active galactic nuclei. Scientific studies of binary systems such as HDE 226868/Cygnus X-1 may lead to further insights into the mechanics of active galaxies.
Black hole
Due to the relatively large strength of the electromagnetic force, black holes forming from the collapse of stars are expected to retain the nearly neutral charge of the star. Rotation, however, is expected to be a universal feature of compact astrophysical objects. The black-hole candidate binary X-ray source GRS 1915+105 appears to have an angular momentum near the maximum allowed value. That uncharged limit is
Bahcall–Wolf cusp
Bahcall–Wolf cusp refers to a particular distribution of stars around a massive black hole at the center of a galaxy or globular cluster. If the nucleus containing the black hole is sufficiently old, exchange of orbital energy between stars drives their distribution toward a characteristic form, such that the density of stars, "ρ", varies with distance from the black hole, "r", as
List of most massive black holes
Although SMBHs are currently theorized to exist in almost all massive galaxies, more massive black holes are rare; with only fewer than several dozen having been discovered to date. There is extreme difficulty in determining a mass of a particular SMBH, and so they still remain in the field of open research. SMBHs with accurate masses are limited only to galaxies within the Laniakea Supercluster and to active galactic nuclei.
NGC 1600
NGC 1600 has a diffuse distribution of stars near its center, caused by the influence of the galaxy's central black hole. Despite NGC 1600 being of typical size, the supermassive black hole at its center is unusually large, with a mass of 17 billion solar masses (), making it one of the largest known. At the time of the determination of the size of the black hole, in 2016, it was found to be unusual in its location in relation to the galaxy population of the region. Previously, extremely large black holes were only found in the hearts of large dense rich clusters, the galaxy group for which NGC 1600 is found is only an average galaxy group and not a rich cluster. This discovery could signify previously unknown populations of very large black holes, and that black hole growth models may be incorrect or incomplete.
Spiral galaxy
Many bulges are thought to host a supermassive black hole at their centers. Such black holes have never been directly observed, but many indirect proofs exist. In our own galaxy, for instance, the object called Sagittarius A* is believed to be a supermassive black hole.
Hercules A
3C 348, the galaxy at the image center, appears to be a relatively normal elliptical galaxy in visible light. When imaged in radio waves, however, plasma jets over one million light years long appear. Detailed analyses indicate that the galaxy is actually over 1,000 times more massive (approx. 10 solar masses) than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive (approx. 4 billion solar masses) than the black hole at our Milky Way's center, one of the largest known. The physics that creates the jets is poorly understood, with a likely energy source being matter ejected perpendicular to the accretion disc of the central black hole.
Black hole
Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses () may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.
Introduction to general relativity
When mass is concentrated into a sufficiently compact region of space, general relativity predicts the formation of a black hole – a region of space with a gravitational effect so strong that not even light can escape. Certain types of black holes are thought to be the final state in the evolution of massive stars. On the other hand, supermassive black holes with the mass of millions or billions of Suns are assumed to reside in the cores of most galaxies, and they play a key role in current models of how galaxies have formed over the past billions of years.
Ultra-high-energy cosmic ray
The source of such high energy particles has been a mystery for many years. Recent results from the Pierre Auger Observatory show that ultra-high-energy cosmic ray arrival directions appear to be correlated with extragalactic supermassive black holes at the center of nearby galaxies called active galactic nuclei (AGN).
However, since the angular correlation scale used is fairly large (3.1 degrees) these results do not unambiguously identify the origins of such cosmic ray particles. The AGN could merely be closely associated with the actual sources, for example in galaxies or other astrophysical objects that are clumped with matter on large scales within 100 Mpc.
Black hole
The gravitational collapse of heavy stars is assumed to be responsible for the formation of stellar mass black holes. Star formation in the early universe may have resulted in very massive stars, which upon their collapse would have produced black holes of up to . These black holes could be the seeds of the supermassive black holes found in the centers of most galaxies. It has further been suggested that supermassive black holes with typical masses of ~ could have formed from the direct collapse of gas clouds in the young universe. Some candidates for such objects have been found in observations of the young universe.
Sagittarius (constellation)
Sagittarius contains several well-known nebulae, including the Lagoon Nebula (Messier 8), near λ Sagittarii; the Omega Nebula (Messier 17), near the border with Scutum; and the Trifid Nebula (Messier 20), a large nebula containing some very young, hot stars.In addition, several other nebulae have been located within Sagittarius and are of interest to astronomy.In 1999 a violent outburst at V4641 Sgr was thought to have revealed the location of the closest known black hole to Earth, but later investigation increased its estimated distance by a factor of 15. The complex radio source Sagittarius A is also in Sagittarius, near its western boundary with Ophiuchus. Astronomers believe that one of its components, known as Sagittarius A*, is associated with a supermassive black hole at the center of the galaxy, with a mass of 2.6 million solar masses. The Sagittarius Dwarf Elliptical Galaxy is located just outside the Milky Way.
Active galactic nucleus
Today, AGN are a major topic of astrophysical research, both observational and theoretical. AGN research encompasses observational surveys to find AGN over broad ranges of luminosity and redshift, examination of the cosmic evolution and growth of black holes, studies of the physics of black hole accretion and the emission of electromagnetic radiation from AGN, examination of the properties of jets and outflows of matter from AGN, and the impact of black hole accretion and quasar activity on galaxy evolution.
Central massive object
The most massive galaxies are thought to always contain a supermassive black hole (SBH); these galaxies do not contain nuclear star clusters, and the CMO is identified with the SBH. Fainter galaxies usually contain a nuclear star cluster (NSC). In most of these galaxies it is not known whether a supermassive black hole is present, and the CMO is identified with the NSC. A few galaxies, for instance the Milky Way and NGC 4395, are known to contain both a SBH and a NSC.
Active galactic nucleus
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. Radiatively inefficient AGN would be expected to lack many of the characteristic features of standard AGN with an accretion disc.
Massive compact halo object
Neutron stars, unlike black holes, are not heavy enough to collapse completely, and instead form a material rather like that of an atomic nucleus (sometimes informally called neutronium). After sufficient time these stars could radiate away enough energy to become cold enough that they would be too faint to see. Likewise, old white dwarfs may also become cold and dead, eventually becoming black dwarfs, although the universe is not thought to be old enough for any stars to have reached this stage.
Black hole
The Event Horizon Telescope (EHT), however, run by MIT's Haystack Observatory, is an attempt to directly observe the immediate environment of the event horizon of Sagittarius A*, the black hole at the centre of the Milky Way, and to produce a silhouetted image of it. The first such image may appear as early as 2018. In 2015, the EHT managed to detect magnetic fields just outside the event horizon of Sagittarius A*, and even discern some of their properties. The existence of magnetic fields had been predicted by theoretical studies of black holes.
Hen 2-10
The presence of SSCs near the center of the galaxy, and not a singular nuclear star cluster (NSC) has led some to believe that Hen 2-10 is a galaxy in its early years. The presence of the black hole is seen to be evidence of the dissipationless model of NSC formation. In this model, the SSCs will move to the center and form a singular NSC. Due to the black hole's relatively small mass, it is not believed to have a major effect on the timescale of this motion, although it is not yet understood how the black hole will affect the NSC formation. Ignoring the black hole indicates that the NSC should be fully formed in a few hundred million years.
List of most massive stars
Black holes are the end point evolution of massive stars. Technically they are not stars, as they no longer generate heat and light via nuclear fusion in their cores.
Active galactic nucleus
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much higher than normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy". The radiation from an AGN is believed to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
Active galactic nucleus
In the standard model of AGN, cold material close to a black hole forms an accretion disc. Dissipative processes in the accretion disc transport matter inwards and angular momentum outwards, while causing the accretion disc to heat up. The expected spectrum of an accretion disc peaks in the optical-ultraviolet waveband; in addition, a corona of hot material forms above the accretion disc and can inverse-Compton scatter photons up to X-ray energies. The radiation from the accretion disc excites cold atomic material close to the black hole and this in turn radiates at particular emission lines. A large fraction of the AGN's radiation may be obscured by interstellar gas and dust close to the accretion disc, but (in a steady-state situation) this will be re-radiated at some other waveband, most likely the infrared.
Andromeda Galaxy
While at the initial time of its discovery it was hypothesized that the brighter portion of the double nucleus is the remnant of a small galaxy "cannibalized" by Andromeda Galaxy, this is no longer considered a viable explanation, largely because such a nucleus would have an exceedingly short lifetime due to tidal disruption by the central black hole. While this could be partially resolved if P1 had its own black hole to stabilize it, the distribution of stars in P1 does not suggest that there is a black hole at its center.
NGC 5643
The galaxy has an low-luminosity active galactic nucleus of Seyfert 2 type and is also an luminous infrared galaxy. The galaxy has a double sided diffuse radiojet. The galaxy exhibits an extended emission line region elongated in a direction close to the radio position angle of 87°±3°. Chris Simpson et al. analysed images takes from WFPC2 camera of the Hubble Space Telescope in [O III] λ5007 and Hα and found emission extending eastward for at least 1.8 kpc and in the [O III]/Hα map a well-defined V-shaped structure that they identified as the projection of a tridimensional ionisation cone, which shares the same axis with the radio emission. A dust lanes perpendicular to this axis obstructs the nucleus from direct view. A disk of material was found when the data cubes of VLT were analysed. It is aligned with the nucleus and circles it and it possibly provides gas to the active galactic nucleus. The mass of the supermassive black hole has been estimated based on the galaxy stellar velocity dispersion to be 10 M⊙. It has been proposed that the gas outflow has led to star formation on two locations on the bar of the galaxy which lie at the location where the gas from the nucleus encounters the dense material of the bar.
Ophiuchus
Ophiuchus contains several star clusters, such as IC 4665, NGC 6633, M9, M10, M12, M14, M19, M62, and M107, as well as the nebula IC 4603-4604.
M10 is a fairly close globular cluster, only 20,000 light-years from Earth. It has a magnitude of 6.6 and is a Shapley class VII cluster. This means that it has "intermediate" concentration; it is only somewhat concentrated towards its center.
The unusual galaxy merger remnant and starburst galaxy NGC 6240 is also in Ophiuchus. At a distance of 400 million light-years, this "butterfly-shaped" galaxy has two supermassive black holes 3,000 light-years apart. Confirmation of the fact that both nuclei contain black holes was obtained by spectra from the Chandra X-ray Observatory. Astronomers estimate that the black holes will merge in another billion years. NGC 6240 also has an unusually high rate of star formation, classifying it as a starburst galaxy. This is likely due to the heat generated by the orbiting black holes and the aftermath of the collision.
Black hole
The Hawking radiation for an astrophysical black hole is predicted to be very weak and would thus be exceedingly difficult to detect from Earth. A possible exception, however, is the burst of gamma rays emitted in the last stage of the evaporation of primordial black holes. Searches for such flashes have proven unsuccessful and provide stringent limits on the possibility of existence of low mass primordial black holes. NASA's Fermi Gamma-ray Space Telescope launched in 2008 will continue the search for these flashes.
MS 0735.6+7421
MS 0735.6+7421 is a galaxy cluster located in the constellation Camelopardalis, approximately 2.6 billion light-years away. It is notable as the location of one of the largest central galactic black holes in the known universe, which has also apparently produced the most powerful active galactic nucleus eruption ever discovered since the Big Bang.
47 Tucanae
It is not yet clear whether 47 Tucanae hosts a central black hole. Hubble Space Telescope data constrain the mass of any possible black hole at the cluster's center to be less than approximately 1,500 solar masses. However, in February, 2017, astronomers announced that a black hole of some 2,200 solar masses may be located in the cluster; the researchers detected the black hole's signature from the motions and distributions of pulsars in the cluster. However, a recent analysis of an updated and more extensive timing data set on these pulsars provides no solid evidence in favor of the existence of a black hole.
Quasar
The power of quasars originates from supermassive black holes that are believed to exist at the core of most galaxies. The Doppler shifts of stars near the cores of galaxies indicate that they are rotating around tremendous masses with very steep gravity gradients, suggesting black holes.
John Michell
Michell suggested that there might be many "dark stars" in the universe, and today astronomers believe that black holes do indeed exist at the centers of most galaxies. Similarly, Michell proposed that astronomers could detect "dark stars" by looking for star systems which behaved gravitationally like two stars, but where only one star could be seen. Michell argued that this would show the presence of a "dark star". It was an extraordinarily accurate prediction. All of the dozen candidate stellar black holes in our galaxy (the Milky Way) are in X-ray compact binary systems.
Black hole
In 1931, Subrahmanyan Chandrasekhar calculated, using special relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at ) has no stable solutions. His arguments were opposed by many of his contemporaries like Eddington and Lev Landau, who argued that some yet unknown mechanism would stop the collapse. They were partly correct: a white dwarf slightly more massive than the Chandrasekhar limit will collapse into a neutron star, which is itself stable. But in 1939, Robert Oppenheimer and others predicted that neutron stars above another limit (the Tolman–Oppenheimer–Volkoff limit) would collapse further for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes. Their original calculations, based on the Pauli exclusion principle, gave it as ; subsequent consideration of strong force-mediated neutron-neutron repulsion raised the estimate to approximately to . Observations of the neutron star merger GW170817, which is thought to have generated a black hole shortly afterward, have refined the TOV limit estimate to ~.
Black hole
The evidence for the existence of stellar and supermassive black holes implies that in order for black holes to not form, general relativity must fail as a theory of gravity, perhaps due to the onset of quantum mechanical corrections. A much anticipated feature of a theory of quantum gravity is that it will not feature singularities or event horizons and thus black holes would not be real artifacts. For example, in the fuzzball model based on string theory, the individual states of a black hole solution do not generally have an event horizon or singularity, but for a classical/semi-classical observer the statistical average of such states appears just as an ordinary black hole as deduced from general relativity.
String theory
In general relativity, a black hole is defined as a region of spacetime in which the gravitational field is so strong that no particle or radiation can escape. In the currently accepted models of stellar evolution, black holes are thought to arise when massive stars undergo gravitational collapse, and many galaxies are thought to contain supermassive black holes at their centers. Black holes are also important for theoretical reasons, as they present profound challenges for theorists attempting to understand the quantum aspects of gravity. String theory has proved to be an important tool for investigating the theoretical properties of black holes because it provides a framework in which theorists can study their thermodynamics.
Globular cluster
Globular clusters have a very high star density, and therefore close interactions and near-collisions of stars occur relatively often. Due to these chance encounters, some exotic classes of stars, such as blue stragglers, millisecond pulsars and low-mass X-ray binaries, are much more common in globular clusters. A blue straggler is formed from the merger of two stars, possibly as a result of an encounter with a binary system. The resulting star has a higher temperature than comparable stars in the cluster with the same luminosity, and thus differs from the main sequence stars formed at the beginning of the cluster.
Astronomers have searched for black holes within globular clusters since the 1970s. The resolution requirements for this task, however, are exacting, and it is only with the Hubble space telescope that the first confirmed discoveries have been made. In independent programs, a intermediate-mass black hole has been suggested to exist based on HST observations in the globular cluster M15 and a black hole in the Mayall II cluster in the Andromeda Galaxy. Both x-ray and radio emissions from Mayall II appear to be consistent with an intermediate-mass black hole.
Messier 58
Messier 58 has a low-luminosity active galactic nucleus, where a starburst may be present as well as a supermassive black hole with a mass of around 70 million solar masses. It is also one of the very few galaxies known to possess a UCNR ("Ultra-Compact Nuclear Ring"), a series of star-forming regions located in a very small ring around the center of the galaxy.
Ultra-high-energy cosmic ray
Some of the supermassive black holes in AGN are known to be rotating, as in the Seyfert galaxy MCG 6-30-15 with time-variability in their inner accretion disks. Black hole spin is a potentially effective agent to drive UHECR production, provided ions are suitably launched to circumvent limiting factors deep within the galactic nucleus, notably curvature radiation and inelastic scattering with radiation from the inner disk. Low-luminosity, intermittent Seyfert galaxies may meet the requirements with the formation of a linear accelerator several light years away from the nucleus, yet within their extended ion tori whose UV radiation ensures a supply of ionic contaminants. The corresponding electric fields are small, on the order of 10 V/cm, whereby the observed UHECRs are indicative for the astronomical size of the source. Improved statistics by the Pierre Auger Observatory will be instrumental in identifying the presently tentative association of UHECRs (from the Local Universe) with Seyferts and LINERs.
Active galactic nucleus
The observed characteristics of an AGN depend on several properties such as the mass of the central black hole, the rate of gas accretion onto the black hole, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets.
NGC 2768
In the centre of the galaxy are two tiny, S-shaped symmetric jets. These two flows of material travel outwards from the galactic centre along curved paths, and are masked by the tangle of dark dust lanes that spans the body of the galaxy. These jets are a sign of a very active centre, where lies a supermassive black hole. This speeds up and sucks in gas from the nearby space, creating a stream of material swirling inwards towards the black hole known as an accretion disc. This disk throws off material in very energetic outbursts, creating structures like the jets.
Active galactic nucleus
Most luminous classes of AGN (radio-loud and radio-quiet) seem to have been much more numerous in the early universe. This suggests that massive black holes formed early on and that the conditions for the formation of luminous AGN were more common in the early universe, such as a much higher availability of cold gas near the centre of galaxies than at present. It also implies that many objects that were once luminous quasars are now much less luminous, or entirely quiescent. The evolution of the low-luminosity AGN population is much less well understood due to the difficulty of observing these objects at high redshifts.Dusty surprise around giant black hole
Extreme mass ratio inspiral
It is currently thought that the centers of most (large) galaxies consist of a supermassive black hole of 10 to 10 solar masses () surrounded by a cluster of 10 to 10 stars maybe 10 light-years across, called the nucleus. The orbits of the objects around the central supermassive black hole are continually perturbed by two-body interactions with other objects in the nucleus, changing the shape of the orbit. Occasionally, an object may pass close enough to the central supermassive black hole for its orbit to produce large amounts of gravitational waves, significantly affecting the orbit. Under specific conditions such an orbit may become an EMRI.
Quasar
A quasar () (also known as a QSO or quasi-stellar object) is an extremely luminous active galactic nucleus (AGN). It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of times the mass of our Sun. In quasars and other types of AGN, the black hole is surrounded by a gaseous accretion disk. As gas falls toward the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum. The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way.
Massive compact halo object
MACHOs may sometimes be considered to include black holes. Black holes are truly black in that they emit no light and any light shone upon them is absorbed and not reflected. It is thought possible that there is a halo of black holes surrounding the Milky Way.
A black hole can sometimes be detected by the halo of bright gas and dust that forms around it as an accretion disc being pulled in by the black hole's gravity. Such a disk can generate jets of gas that are shot out away from the black hole because it cannot be absorbed quickly enough. An isolated black hole, however, would not have an accretion disk and would only be detectable by gravitational lensing.
Cosmologists doubt they make up a majority of dark matter because the black holes are at isolated points of the galaxy. The largest contributor to the missing mass must be spread throughout the galaxy to balance the gravity. A minority of physicists, including Chapline and Laughlin, believe that the widely accepted model of the black hole is wrong and needs to be replaced by a new model, the dark-energy star; in the general case for the suggested new model, the cosmological distribution of dark energy would be slightly lumpy and dark-energy stars of primordial type might be a possible candidate for MACHOs.
Messier 59
The core contains a supermassive black hole (SMBH), with a mass that has been estimated to be 270 million times the mass of the Sun, and counter-rotates with respect of the rest of the galaxy, being bluer. The SMBH is quiescent, but is detectable as an X-ray and radio source that indicates an outflow. The nucleus contains an embedded stellar disk that is bluer (younger) than the bulge region, with a blue component stretching along a position angle of around 150°. This extended disk feature may be the result of a galactic merger followed by a starburst event.
NGC 4939
NGC 4939 has been characterised as a Seyfert galaxy, a galaxy category which features bright point-like nuclei. NGC 4939 is a type II Seyfert galaxy. Its X ray spectrum is more consistent with a Compton-thick cold reflection source, which means that the source is hidden behind dense material, mainly gas and dust, and the X-ray observed have been reflected, but a Compton-thin transmission model could not be ruled out. The equivalent width of the FeKα line is large, indicating too that it is a Compton-thick source. 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.
Stellar black hole
Our Milky Way galaxy contains several stellar-mass Black Hole Candidates (BHCs) which are closer to us than the supermassive black hole in the Galactic center region. Most of these candidates are members of X-ray binary systems in which the compact object draws matter from its partner via an accretion disk. The probable black holes in these pairs range from three to more than a dozen solar masses.
Great Annihilator
1E1740.7-2942, or the Great Annihilator, is a large black hole thought to be located in the core region of the Milky Way, near the supermassive black hole Sgr A* at the Galactic Center.
It is one of the brightest gamma ray sources found in the Milky Way, producing massive amounts of photon pairs at 511 keV, which usually indicates the annihilation of an electron-positron pair. The Great Annihilator also has a radio source counterpart that emits jets approximately three light-years long. These jets are probably synchrotron emissions from positron-electron pairs streaming out at high velocities from the source of antimatter.
Black hole
The proper motions of stars near the center of our own Milky Way provide strong observational evidence that these stars are orbiting a supermassive black hole. Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source Sagittarius A*. By fitting their motions to Keplerian orbits, the astronomers were able to infer, in 1998, that a 2.6 million object must be contained in a volume with a radius of 0.02 light-years to cause the motions of those stars. Since then, one of the stars—called S2—has completed a full orbit. From the orbital data, astronomers were able to refine the calculations of the mass to 4.3 million and a radius of less than 0.002 light years for the object causing the orbital motion of those stars. The upper limit on the object's size is still too large to test whether it is smaller than its Schwarzschild radius; nevertheless, these observations strongly suggest that the central object is a supermassive black hole as there are no other plausible scenarios for confining so much invisible mass into such a small volume. Additionally, there is some observational evidence that this object might possess an event horizon, a feature unique to black holes.
NGC 3489
NGC 3489 has an active galactic nucleus, which has been categorised based on its spectrum as a type 2 Seyfert galaxy or, based on the nuclear [O I] emission strength, which lies between that of H II nuclei and LINER, a transition object. This kind of transition emission could be attributed to post AGB stars located in the core. A supermassive black hole which accretes material in the centre of the galaxy is believed to be the cause of nuclear activity. In the centre of NGC 3489 lies a black hole with estimated mass based on velocity dispersion.
Messier 108
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. The supermassive black hole at the core has an estimated mass equal to 24 million times the mass of the Sun.
Intermediate-mass black hole
Intermediate-mass black holes are too massive to be formed by the collapse of a single star, which is how stellar black holes are thought to form. Their environments lack the extreme conditions—i.e., high density and velocities observed at the centers of galaxies—which seemingly lead to the formation of supermassive black holes. There are three postulated formation scenarios for IMBHs. The first is the merging of stellar mass black holes and other compact objects by means of accretion. The second one is the runaway collision of massive stars in dense stellar clusters and the collapse of the collision product into an IMBH. The third is that they are primordial black holes formed in the Big Bang.
MS 0735.6+7421
Using data from the Chandra Space Telescope, scientists have deduced that an eruption has been occurring for the last 100 million years at the heart of the galaxy cluster, releasing as much energy over this time as hundreds of millions of gamma ray bursts. (The amount of energy released in a year is thus equivalent to several GRBs.) The remnants of the eruption are seen as two cavities on either side of a large central galaxy. If this outburst, with a total energy budget of more than 10 J, was caused by a black hole accretion event, it must have consumed nearly 600 million solar masses. Work done by Brian McNamara et al. (2008) point out the striking possibility that the outburst was not the result of an accretion event, but was instead powered by the rotation of the black hole. Moreover, the scientists mentioned the possibility that the central black hole in MS 0735.6+7421 could be one of the biggest black holes inhabiting the visible universe. This speculation is supported by the fact that the central cD Galaxy inside MS 0735.6+7421 possess the largest break radius known, as of today. With a calculated light deficit of more than 20 billion solar luminosities and an assumed light-to-mass ratio of 3, this yields a central black hole mass much above 10 billion solar masses, as far as the break radius was caused by the merger of several black holes in the past. In combination with the gargantuan energy outburst it is therefore very likely that MS 0735.6+7421 hosts a supermassive black hole in its core.
The cluster has a red shift of 64,800 ± 900 km/s and an apparent size of 25′.
NGC 4278
NGC 4278 is an elliptical galaxy. Its nucleus has been found to be active (AGN) and based on its spectrum has been identified as a LINER. The most accepted theory for the power source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. In the centre of NGC 4278 lies a supermassive black hole with an estimated mass based on stellar velocity dispersion. The X-ray emission of the nucleus is consistent with one of a black hole fed by a low radiative efficiency accretion flow.
Hobby–Eberly Telescope
As reported in "Nature" of 28 November 2012, astronomers have used the Hobby–Eberly Telescope to measure the mass of an extraordinarily large black hole (with mass approximates 17 billion Suns), possibly the largest black hole found so far. It has been found in the compact, lenticular galaxy NGC 1277, which lies 220 million light-years away in the constellation Perseus. The black hole has approximately 59 percent of the mass of the bulge of this spiral galaxy (14 percent of the total stellar mass of the galaxy).
Triangulum Galaxy
Triangulum is classified as unbarred, but an analysis of the galaxy shape shows what may be a weak bar-like structure about the galactic nucleus. The radial extent of this structure is about 0.8 kpc. The nucleus of this galaxy is an H II region, and it contains an ultraluminous X-ray source with an emission of , which is the most luminous source of X-rays in the Local Group of galaxies. This source is modulated by 20% over a 106-day cycle. However, the nucleus does not appear to contain a supermassive black hole, as an upper limit of 3,000 solar masses is placed on the mass of a central black hole based upon the velocity of stars in the core region.
Stellar black hole
The gravitational collapse of a star is a natural process that can produce a black hole. It is inevitable at the end of the life of a star, when all stellar energy sources are exhausted. If the mass of the collapsing part of the star is below the Tolman–Oppenheimer–Volkoff (TOV) limit for neutron-degenerate matter, the end product is a compact star — either a white dwarf (for masses below the Chandrasekhar limit) or a neutron star or a (hypothetical) quark star. If the collapsing star has a mass exceeding the TOV limit, the crush will continue until zero volume is achieved and a black hole is formed around that point in space.
M–sigma relation
The smallest supermassive black hole with a well-determined mass has . The existence of black holes in the mass range ("intermediate-mass black holes") is predicted by the M–σ relation in low-mass galaxies, and the existence of intermediate-mass black holes has been reasonably well established in a number of galaxies that contain active galactic nuclei, although the values of M in these galaxies are very uncertain.
No clear evidence has been found for ultra-massive black holes with masses above , although this may be an expected consequence of the observed upper limit to σ.
NGC 1266
Two hypotheses exist to explain NGC 1266's nuclear activity and excessive far-IR emission. Either a heavily obscured ultracompact starburst is present in the nuclear regions, or a powerful buried AGN is present, beyond what has been inferred from other observations. Neither scenario is without problems. The black hole at the center of the galaxy is likely growing according to the M–sigma relation, and eventually the outflow will result in the removal of the majority of the gas from the nucleus.
Astrophysical X-ray source
Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas. They are a subclass of active galactic nuclei (AGN), and are thought to contain supermassive black holes.
Black hole
The evidence for stellar black holes strongly relies on the existence of an upper limit for the mass of a neutron star. The size of this limit heavily depends on the assumptions made about the properties of dense matter. New exotic phases of matter could push up this bound. A phase of free quarks at high density might allow the existence of dense quark stars, and some supersymmetric models predict the existence of Q stars. Some extensions of the standard model posit the existence of preons as fundamental building blocks of quarks and leptons, which could hypothetically form preon stars. These hypothetical models could potentially explain a number of observations of stellar black hole candidates. However, it can be shown from arguments in general relativity that any such object will have a maximum mass.
Black hole
It is now widely accepted that the center of nearly every galaxy, not just active ones, contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation, strongly suggests a connection between the formation of the black hole and the galaxy itself.
Another way that the black hole nature of an object may be tested in the future is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected much as light passing through an optic lens. Observations have been made of weak gravitational lensing, in which light rays are deflected by only a few arcseconds. However, it has never been directly observed for a black hole. One possibility for observing gravitational lensing by a black hole would be to observe stars in orbit around the black hole. There are several candidates for such an observation in orbit around Sagittarius A*.
Rotating black hole
A rotating black hole is a black hole that possesses angular momentum. In particular, it rotates about one of its axes of symmetry.
There are four known, exact, black hole solutions to the Einstein field equations, which describe gravity in general relativity. Two of those rotate: the Kerr and Kerr–Newman black holes. It is generally believed that every black hole decays rapidly to a stable black hole; and, by the no-hair theorem, that (except for quantum fluctuations) stable black holes can be completely described at any moment in time by these eleven numbers:
Virgo (constellation)
NGC 4438 is a peculiar galaxy with an active galactic nucleus, at a distance of from Earth (redshift 0.0035). Its supermassive black hole is ejecting jets of matter, creating bubbles with a diameter of up to .
APM 08279+5255
From these observations APM 08279+5255 is a giant elliptical galaxy with large amounts of gas and dust and an active galactic nucleus (AGN) at its core. The AGN is radio-quiet with no evidence for a relativistic jet. It is powered by one of the largest known supermassive black holes: 23 billion solar masses (based on the molecular disk velocities); or alternatively 10 billion solar masses (based on reverberation mapping). The black hole is surrounded by an accretion disk of material spiraling into it, a few parsecs in size. Further out is a dust torus, a doughnut shaped cloud of dust and gas with a radius of about 100 parsecs. Both the accretion disk and dust torus appear to be almost face-on to us. The radiation from the molecular gas is coming from a flattened disk at the center of the galaxy with a radius of 550 pc. This is also the starburst region of the galaxy. The gas is heated both by activity in the AGN and by the newly forming stars.
General relativity
Whenever the ratio of an object's mass to its radius becomes sufficiently large, general relativity predicts the formation of a black hole, a region of space from which nothing, not even light, can escape. In the currently accepted models of stellar evolution, neutron stars of around 1.4 solar masses, and stellar black holes with a few to a few dozen solar masses, are thought to be the final state for the evolution of massive stars. Usually a galaxy has one supermassive black hole with a few million to a few billion solar masses in its center, and its presence is thought to have played an important role in the formation of the galaxy and larger cosmic structures.
Astronomically, the most important property of compact objects is that they provide a supremely efficient mechanism for converting gravitational energy into electromagnetic radiation. Accretion, the falling of dust or gaseous matter onto stellar or supermassive black holes, is thought to be responsible for some spectacularly luminous astronomical objects, notably diverse kinds of active galactic nuclei on galactic scales and stellar-size objects such as microquasars. In particular, accretion can lead to relativistic jets, focused beams of highly energetic particles that are being flung into space at almost light speed.
General relativity plays a central role in modelling all these phenomena, and observations provide strong evidence for the existence of black holes with the properties predicted by the theory.
Stellar black hole
A stellar black hole (or stellar-mass black hole) is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. The process is observed as a hypernova explosion or as a gamma ray burst. These black holes are also referred to as collapsars.
Near-extremal black hole
In theoretical physics, a near-extremal black hole is a black hole which is not far from the minimal possible mass that can be compatible with the given charges and angular momentum. The calculations of the properties of near-extremal black holes are usually performed using perturbation theory around the extremal black hole; the expansion parameter is called non-extremality.
Binary black hole
When two galaxies collide, the supermassive black holes at their centers do not hit head-on, but would shoot past each other if some mechanism did not bring them together. The most important mechanism is dynamical friction, which brings the black holes to within a few parsecs of each other. At this distance, they form a bound, binary system. The binary system must lose orbital energy somehow, for the black holes to orbit more closely or merge.
Phoenix Cluster
The central elliptical cD galaxy of this cluster hosts an active galactic nucleus, which is powered by a central supermassive black hole. The central black hole has an estimated mass on the order of 20 billion . This makes it one of the most massive black holes known in the universe, 5,000 times the mass of the black hole at the center of the Milky Way. The diameter of the black hole's immense event horizon is on the order of 118 billion kilometers, 19 times the distance from the Sun to Pluto, and has the mass equivalent to that of two dwarf galaxies. The central black hole is devouring matter and growing at a rate of 60 every year.
NGC 2336
Scattered dust lanes which don't fit into a spiral structure have been observed in the nuclear region of the galaxy. No emission has been detected in the radiowaves and HI and Ha imaging of the nucleus of NGC 2336. The nucleus is small, with an apparent diameter of 5 arcseconds, while the bulge is large, with a radius of 17 arcseconds. In the centre of NGC 2336 lies a supermassive black hole whose mass is estimated to be 30 million (10) based on Ks bulge luminosity.
Gamma-ray burst progenitors
While the astrophysical community has yet to settle on a single, universally favored model for the progenitors of short GRBs, the generally preferred model is the merger of two compact objects as a result of gravitational inspiral: two neutron stars, or a neutron star and a black hole. While thought to be rare in the Universe, a small number of cases of close neutron star - neutron star binaries are known in our Galaxy, and neutron star - black hole binaries are believed to exist as well. According to Einstein's theory of general relativity, systems of this nature will slowly lose energy due to gravitational radiation and the two degenerate objects will spiral closer and closer together, until in the last few moments, tidal forces rip the neutron star (or stars) apart and an immense amount of energy is liberated before the matter plunges into a single black hole. The whole process is believed to occur extremely quickly and be completely over within a few seconds, accounting for the short nature of these bursts. Unlike long-duration bursts, there is no conventional star to explode and therefore no supernova.
Sagittarius A*
Ultimately, what is seen is not the black hole itself, but observations that are consistent only if there is a black hole present near Sgr A*. In the case of such a black hole, the observed radio and infrared energy emanates from gas and dust heated to millions of degrees while falling into the black hole. The black hole itself is thought to emit only Hawking radiation at a negligible temperature, on the order of 10 kelvin.
The European Space Agency's gamma-ray observatory INTEGRAL observed gamma rays interacting with the nearby giant molecular cloud Sagittarius B2, causing X-ray emission from the cloud. The total luminosity from this outburst (≈1,5 erg/s) is estimated to be a million times stronger than the current output from Sgr A* and is comparable with a typical active galactic nucleus. In 2011 this conclusion was supported by Japanese astronomers observing the Milky Way's center with the "Suzaku" satellite.
Astrosat
In particular, the mission will train its instruments at active galactic nuclei (such as that of the core of the Milky Way), which are believed to contain super-massive black holes.
Galactic Center
In addition to the paradox of youth, there is also a "conundrum of old age" associated with the distribution of the old stars at the Galactic Center. Theoretical models had predicted that the old stars—which far outnumber young stars—should have a steeply-rising density near the black hole, a so-called Bahcall–Wolf cusp. Instead, it was discovered in 2009 that the density of the old stars peaks at a distance of roughly 0.5 parsec from Sgr A*, then falls inward: instead of a dense cluster, there is a "hole", or core, around the black hole. Several suggestions have been put forward to explain this puzzling observation, but none is completely satisfactory. For instance, although the black hole would eat stars near it, creating a region of low density, this region would be much smaller than a parsec. Because the observed stars are a fraction of the total number, it is theoretically possible that the overall stellar distribution is different than what is observed, although no plausible models of this sort have yet been proposed.
False vacuum
In a study posted on the arXiv in March 2015, it was pointed out that the vacuum decay rate could be vastly increased in the vicinity of black holes, which would serve as a nucleation seed. According to this study a potentially catastrophic vacuum decay could be triggered any time by primordial black holes, should they exist. If particle collisions produce mini black holes then energetic collisions such as the ones produced in the Large Hadron Collider (LHC) could trigger such a vacuum decay event. However the authors say that this is not a reason to expect the universe to collapse, because if such mini black holes can be created in collisions, they would also be created in the much more energetic collisions of cosmic radiation particles with planetary surfaces. And if there are primordial mini black holes they should have triggered the vacuum decay long ago. Rather, they see their calculations as evidence that there must be something else preventing vacuum decay.
Stellar black hole
There is observational evidence for two other types of black holes, which are much more massive than stellar black holes. They are intermediate-mass black holes (in the centre of globular clusters) and supermassive black holes in the centre of the Milky Way and other galaxies.
Supermassive black hole
On March 28, 2011, a supermassive black hole was seen tearing a mid-size star apart. That is the only likely explanation of the observations that day of sudden X-ray radiation and the follow-up broad-band observations. The source was previously an inactive galactic nucleus, and from study of the outburst the galactic nucleus is estimated to be a SMBH with mass of the order of a million solar masses. This rare event is assumed to be a relativistic outflow (material being emitted in a jet at a significant fraction of the speed of light) from a star tidally disrupted by the SMBH. A significant fraction of a solar mass of material is expected to have accreted onto the SMBH. Subsequent long-term observation will allow this assumption to be confirmed if the emission from the jet decays at the expected rate for mass accretion onto a SMBH.
Black holes in fiction
In 1958, David Finkelstein identified the Schwarzschild surface of a black hole as an event horizon, extending the commonplace notion that objects beyond a horizon cannot be seen, calling it "a perfect unidirectional membrane: causal influences can cross it in only one direction." This result helped usher in the golden age of general relativity, which was marked by general relativity and black holes becoming mainstream subjects of research. Later tales (below) tend to portray black holes in a fashion more thoroughly in accord with modern understanding. An early term for the black hole produced by stellar collapse was "collapsar" (short for collapsed star) with the term "black hole" itself being introduced by John Wheeler in 1967 and adopted enthusiastically by science fiction writers. In science fiction stories written up to this date (Early works), black holes are called by a variety of more or less suggestive names, including "black" and "hole" used in isolation; after 1969, almost all works use Wheeler's combined term "black hole."
In 1971, Hawking introduced the idea that black holes may exist that are smaller than stellar mass, "micro black holes", possibly formed as primordial black holes during the high-density phase of the big bang. Some stories refer to these as "quantum black holes," distinguishing them from astrophysical black holes. In 1975, Hawking pointed out that such small holes would evaporate due to the emission of Hawking radiation.
Andromeda Galaxy
In 2012, a microquasar, a radio burst emanating from a smaller black hole, was detected in the Andromeda Galaxy. The progenitor black hole is located near the galactic center and has about 10 formula_1. Discovered through a data collected by the European Space Agency's XMM-Newton probe, and subsequently observed by NASA's Swift Gamma-Ray Burst Mission and Chandra X-Ray Observatory, the Very Large Array, and the Very Long Baseline Array, the microquasar was the first observed within the Andromeda Galaxy and the first outside of the Milky Way Galaxy.
Edwin Ernest Salpeter
In 1964 Salpeter and independently Yakov B. Zel'dovich were the first to suggest that accretion discs around massive black holes are responsible for the huge amounts of energy radiated by quasars (which are the brightest active galactic nuclei). This is currently the most accepted explanation for the physical origin of active galactic nuclei and the associated extragalactic relativistic jets.
Seyfert galaxy
The majority of active galaxies are very distant and show large Doppler shifts. This suggests that active galaxies occurred in the early Universe and, due to cosmic inflation, are receding away from the Milky Way at very high speeds. Quasars are the furthest active galaxies, some of them being observed at distances 12 billion light years away. Seyfert galaxies are much closer than quasars. Because light has a finite speed, looking across large distances in the Universe is equivalent to looking back in time. Therefore, the observation of active galactic nuclei at large distances and their scarcity in the nearby Universe suggests that they were much more common in the early Universe, implying that active galactic nuclei could be early stages of galactic evolution. This leads to the question about what would be the local (modern-day) counterparts of AGNs found at large redshifts. It has been proposed that NLSy1s could be the small redshift counterparts of quasars found at large redshifts (z>4). The two have many similar properties, for example: high metallicities or similar pattern of emission lines (strong Fe [II], weak O [III]). Some observations suggest that AGN emission from the nucleus is not spherically symmetric and that the nucleus often shows axial symmetry, with radiation escaping in a conical region. Based on these observations, models have been devised to explain the different classes of AGNs as due to their different orientations with respect to the observational line of sight. Such models are called unified models. Unified models explain the difference between Seyfert I and Seyfert II galaxies as being the result of Seyfert II galaxies being surrounded by obscuring toruses which prevent telescopes from seeing the broad line region. Quasars and blazars can be fit quite easily in this model. The main problem of such an unification scheme is trying to explain why some AGN are radio loud while others are radio quiet. It has been suggested that these differences may be due to differences in the spin of the central black hole.
NGC 4636
The central part of NGC 4636 is circular and is surrounded by an elongated fainter envelope, containing a large number of globular clusters. The galaxy has an active galactic nucleus (AGN) that has been categorised as LINER or a type 1.9 Seyfert galaxy. The source of nuclear activity in galaxies is suggested to be a supermassive black hole that accretes material. NGC 4636 harbors a relatively small supermassive black hole with mass , as inferred from the bulge velocity dispersion.
Supermassive black hole
Some galaxies, however, lack any supermassive black holes in their centers. Although most galaxies with no supermassive black holes are very small, dwarf galaxies, one discovery remains mysterious: The supergiant elliptical cD galaxy A2261-BCG has not been found to contain an active supermassive black hole, despite the galaxy being one of the largest galaxies known; ten times the size and one thousand times the mass of the Milky Way. Since a supermassive black hole will only be visible while it is accreting, a supermassive black hole can be nearly invisible, except in its effects on stellar orbits.
Black Eye Galaxy
M64 is a type 2 Seyfert galaxy with an HII/LINER nucleus. The central region is a weak source of radio emission. A soft X-ray source has been detected at the nucleus, which is most likely coming from the circumnuclear region rather than directly from an active galactic nucleus. There is an inner disk of molecular gas that is truncated at a radius of . At present, the non-rotational motions of this disk do not significantly feed the core, but the disk does produce a vigorous rate of star formation. There is also evidence of a recent large inflow of mass.
NGC 3621
This galaxy has an active nucleus that matches a Seyfert 2 optical spectrum, suggesting that a low mass supermassive black hole is present at the core. Based upon the motion of stars in the nucleus, this object may have a mass of up to three million times the mass of the Sun.
List of most massive black holes
A supermassive black hole (SMBH) is the largest type of black hole, on the order of hundreds of thousands to billions of solar masses (), and is theorized to exist in the center of almost all massive galaxies.
Unambiguous dynamical evidence for SMBHs exists only in a handful of galaxies; these include the Milky Way, the Local Group galaxies M31 and M32, and a few galaxies beyond the Local Group, e.g. NGC 4395. In these galaxies, the mean square (or root mean square) velocities of the stars or gas rises as ~1/r near the center, indicating a central point mass. In all other galaxies observed to date, the rms velocities are flat, or even falling, toward the center, making it impossible to state with certainty that a supermassive black hole is present. Nevertheless, it is commonly accepted that the center of nearly every galaxy contains a supermassive black hole. The reason for this assumption is the M-sigma relation, a tight (low scatter) relation between the mass of the hole in the ~10 galaxies with secure detections, and the velocity dispersion of the stars in the bulges of those galaxies. This correlation, although based on just a handful of galaxies, suggests to many astronomers a strong connection between the formation of the black hole and the galaxy itself.
NGC 6951
The nucleus of NGC 6951 is active. It has been classified both as a type 2 Seyfert galaxy and a LINER and it has been suggested that it is in transition form, between a Seyfert galaxy and a very high excitation LINER, with very strong [N II] and [S II] lines. A supermassive black hole which accretes material in the centre of the galaxy is believed to be the cause of the nuclear activity. The upper mass limit of the supermassive black hole at the centre of NGC 6951 is estimated to be between 6 and 14 million based on velocity dispersion. Molecular gas, most probably a circumnuclear dust disk or torus less than 50 parsec in radius, has been detected around the nucleus.
Elliptical galaxy
Every massive elliptical galaxy contains a supermassive black hole at its center. Observations of 46 elliptical galaxies, 20 classical bulges, and 22 pseudobulges show that each contain a black hole at the center. The mass of the black hole is tightly correlated with the mass of the galaxy, evidenced through correlations such as the M–sigma relation which relates the velocity dispersion of the surrounding stars to the mass of the black hole at the center.