An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102-105 solar masses: significantly more than stellar black holes but less than the 105-109 solar mass supermassive black holes. There is as yet no unambiguous detection of an IMBH, but the indirect evidence from various directions is promising.
The strongest evidence for IMBHs comes from a few low-luminosity active galactic nuclei. Due to their activity, these galaxies almost certainly contain accreting black holes, and in some cases the black hole masses can be estimated using the technique of reverberation mapping. For instance, the spiral galaxy NGC 4395 at a distance of about 4 Mpc appears to contain a black hole with mass of about 3.6×105 solar masses.
Some ultra-luminous X ray sources (ULXs) in nearby galaxies are suspected to be IMBHs, with masses of a hundred to a thousand solar masses. The ULXs are observed in star-forming regions (e.g., in starburst galaxy M82), and are seemingly associated with young star clusters which are also observed in these regions. However, only a dynamical mass measurement from the analysis of the optical spectrum of the companion star can unveil the presence of an IMBH as the compact accretor of the ULX.
A few globular clusters have been claimed to contain IMBHs, based on measurements of the velocities of stars near their centers; the figure shows one candidate object. However none of the claimed detections has stood up to scrutiny. For instance, the data for M31 G1, the object shown in the figure, can be fit equally well without a massive central object.
Finally, the M-sigma relation predicts the existence of black holes with masses of 104 to 106 solar masses in low-luminosity galaxies. There are three main types of black hole: stellar, intermediate, and supermassive.
In November 2004 a team of astronomers reported the discovery of GCIRS 13E, the first intermediate-mass black hole in our galaxy, orbiting three light-years from Sagittarius A*. This medium black hole of 1,300 solar masses is within a cluster of seven stars, possibly the remnant of a massive star cluster that has been stripped down by the Galactic Center. This observation may add support to the idea that supermassive black holes grow by absorbing nearby smaller black holes and stars. However, in 2005, a German research group claimed that the presence of an IMBH near the galactic center is doubtful, based on a dynamical study of the star cluster in which the IMBH was said to reside. An IMBH near the galactic center could also be detected via its perturbations on stars orbiting around the supermassive black hole.
In January 2006 a team led by Philip Kaaret of the University of Iowa announced the discovery of a quasiperiodic oscillation from an intermediate-mass black hole candidate located using NASA's Rossi X-ray Timing Explorer. The candidate, M82 X-1, is orbited by a red giant star that is shedding its atmosphere into the black hole. Neither the existence of the oscillation nor its interpretation as the orbital period of the system are fully accepted by the rest of the scientific community. While the interpretation is quite reasonable, the periodicity claimed is based on only about 4 cycles, meaning that it is quite possible for this to be random variation. If the period is real, it could be either the orbital period, as suggested, or a super-orbital period in the accretion disk, as is seen in many other systems.
In 2009, a team of astronomers led by Sean Farrell discovered HLX-1, an intermediate-mass black hole with a smaller cluster of stars around it, in the galaxy ESO 243-49. This evidence suggested that ESO 243-49 had a galactic collision with HLX-1's galaxy and absorbed the majority of the smaller galaxy's matter.
In 2015 a team at Keio University in Japan found a gas cloud (CO-0.40-0.22) with very wide velocity dispersion. They performed simulations and concluded that a model with a black hole of circa 100,000 solar masses would be the best fit for the velocity distribution. However, a later work pointed out some difficulties with the association of high velocity dispersion clouds with intermediate mass black holes, and proposed that such clouds might be generated by supernovae. Radio observations with the Atacama Large Millimeter/submillimeter Array confirmed absence of an IMBH near CO-0.40-0.22, and found that the large velocity dispersion of the cloud is created by superposition of two molecular clouds with different line-of-sight velocities. 
In 2017, it was announced that a black hole of a few thousand solar masses may be located in the globular cluster 47 Tucanae. This was based on the accelerations and distributions of pulsars in the cluster, however later analysis of an updated and more complete data set on these pulsars finds no positive evidence for this.
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.
47 Tucanae, 47 Tuc (or NGC 104) is a globular cluster located in the constellation Tucana. It is about 4.0 ± 0.35 kpc (13,000 ± 1,100 ly) away from Earth, and 120 light years across. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 50 arcminutes across. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa.
47 Tucanae is the second brightest globular cluster after Omega Centauri, and telescopically reveals about ten thousand stars, many appearing within a small dense central core. The cluster may contain an intermediate-mass black hole.American Astronomical Society 215th meeting
The 215th meeting of the American Astronomical Society (AAS) took place in Washington, D.C., Jan. 3 to Jan. 7, 2010. It is one of the largest astronomy meetings ever to take place as 3,500 astronomers and researchers were expected to attend and give more than 2,200 scientific presentations. The meeting was actually billed as the "largest Astronomy meeting in the universe". An array of discoveries were announced, along with new views of the universe that we inhabit; such as quiet planets like Earth - where life could develop are probably plentiful, even though an abundance of cosmic hurdles exist - such as experienced by our own planet in the past.CO-0.40-0.22
CO-0.40-0.22 is a high velocity compact gas cloud near the centre of the Milky Way. It is 200 light years away from the centre in the central molecular zone. The cloud is in the shape of ellipse. The differences in the velocity, termed velocity dispersion, of the gas is unusually high at 100 km/s. The velocity dispersion may be due to an intermediate-mass black hole with a mass of about 100,000 solar masses. If it exists, this black hole would be the second largest known in the Milky Way.
However, signature of presence of an IMBH was not detected by observations using the Atacama Large Millimeter/submillimeter Array.
The molecular cloud has a mass of 4,000 solar masses. It is located at −0.40°, −0.22° galactic longitude and latitude. The cloud is 0.2° away from Sgr C to the galactic southeast. The gas is moving away from Earth at speeds ranging from 20 to 120 km/s. The spectral lines of carbon monoxide reveal that the gas is dense, and warm and fairly opaque.The gas cloud includes carbon monoxide and hydrogen cyanide molecules. Other molecules detected via microwave spectroscopy include cyanoacetylene, cyclopropenylidene, methanol, silicon monoxide, sulfur monoxide, carbon monosulfide, Thioformaldehyde, Hydrogen isocyanide, Formamide, and ions H2N+ and HCO+.The name followed the precedent set by CO-0.02-0.02, which is another high velocity compact cloud in the central molecular zone. Another example of this naming convention is CO–0.30–0.07.GCIRS 13E
GCIRS 13E is an infrared and radio object near the galactic centre. It is believed to be a cluster of hot massive stars, possibly containing an intermediate-mass black hole (IMBH) at its centre.
GCIRS 13E was first identified as GCIRS 13, which was later resolved into two components GCIRS13E and W. GCIRS 13E was initially modelled as a single object, possibly a binary system. It was even classified as a Wolf-Rayet star because of its strong emission line spectrum, and named WR 101f. It was then resolved into seven Wolf-Rayet and class O stars. The highest-resolution infrared imaging and spectroscopy can now identify 19 objects in GCIRS 13E, of which 15 are dense gaseous regions. The remaining four objects are stars: WN8 and WC9 Wolf-Rayet stars; an OB supergiant; and a K3 giant.The motions of the members of GCIRS 13E appear to indicate a much higher mass than can be accounted for by the visible objects. It has been proposed that there may be an intermediate-mass black hole with a mass of about 1,300 M☉ at its centre. There are a number of problems with this theory. However, the true nature of the cluster remains unknown.GCIRS 13E is a small cluster dominated by a few massive stars. It is thought that massive stars cannot form so close to a supermassive black hole and since such massive stars have a short lifespan it is thought that GCIRS 13E must have migrated inward toward the central black hole within the past 10 million years, probably from about 60 light-years further out than its current orbit. The stars are possibly the remains of a globular cluster where a middleweight black hole such as could develop through runaway star collisions.HLX-1
Hyper-Luminous X-ray source 1, commonly known as HLX-1, is an intermediate-mass black hole candidate located in the galaxy ESO 243-49 about 290 million light-years from Earth . The source was discovered at the Institut de Recherche en Astrophysique et Planétologie (IRAP, formerly the CESR), Toulouse, France and gained interest from the scientific community because of strong evidence supporting it as an intermediate-mass black hole. HLX-1 is possibly the remnant of a dwarf galaxy that may have been in a galactic collision with ESO 243-49.Holmberg II
Holmberg II is a dwarf galaxy in the constellation Ursa Major. Its apparent magnitude is 11,1m and it is 11 million light years away from Earth. The galaxy is dominated by huge glowing gas bubbles, which are regions of star formation.Holmberg II also hosts an ultraluminous X-ray source. One hypothesis suggests that is caused by an intermediate mass black hole that is pulling surrounding material.Holmberg II was discovered by Erik Bertil Holmberg.M82 X-1
M82 X-1 is an ultra-luminous X-ray source located in the galaxy M82. It is a candidate intermediate-mass black hole.Messier 108
Messier 108 (also known as NGC 3556) is a barred spiral galaxy in the constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782. From the perspective of the Earth, this galaxy is seen almost edge-on.
This galaxy is an isolated member of the Ursa Major Cluster of galaxies in the Virgo supercluster. It has a morphological classification of type SBbc in the de Vaucouleurs system, which means it is a barred spiral galaxy with somewhat loosely wound arms. The maximum angular size of the galaxy in the optical band is 11′.1 × 4′.6, and it is inclined 75° to the line of sight.
This galaxy has an estimated mass of 125 billion times the mass of the Sun and includes about 290 ± 80 globular clusters. Examination of the distribution of neutral hydrogen in this galaxy shows shells of expanding gas extending for several kiloparsecs, known as H1 supershells. These may be driven by bursts of star formation activity, resulting in supernovae explosions. Alternatively they may result from an infall of gas from outside the galaxy or by radio jets.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.Messier 54
Messier 54 (also known as M54 or NGC 6715) is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778 and subsequently included in his catalog of comet-like objects.
M54 is easily found in the sky, being close to the star ζ Sagittarii. It is, however, not resolvable into individual stars even with larger amateur telescopes.
Previously thought to belong to the Milky Way at a distance from Earth of about 50,000 light-years, it was discovered in 1994 that M54 most likely belongs to the Sagittarius Dwarf Elliptical Galaxy (SagDEG), making it the first globular cluster formerly thought to be part of our galaxy reassigned to extragalactic status, even if not recognized as such for nearly two and a quarter centuries. As it is located on SagDEG's center, some authors think it actually may be its core; however others have proposed that it is a real globular cluster that fell to the center of this galaxy due to decay of its orbit caused by dynamical friction.Modern estimates now place M54 at a distance of some 87,000 light-years, translating into a true radius of 150 light-years across. It is one of the denser of the globulars, being of class III (I being densest and XII being the least dense). It shines with the luminosity of roughly 850,000 times that of the Sun and has an absolute magnitude of −10.0. In July 2009, a team of astronomers reported that they had found evidence of an intermediate-mass black hole in the core of M54.Messier 62
Messier 62 or M62, also known as NGC 6266, is a globular cluster of stars in the equatorial constellation of Ophiuchus. It was discovered on June 7, 1771 by Charles Messier, then added to his catalogue in 1779.M62 is at a distance of about 22.2 kly from Earth and 5.5 kly from the Galactic center. It is among the ten most massive and luminous globular clusters in the Milky Way, showing an integrated absolute magnitude of –9.18. The cluster has an estimated mass of 1.22×106 M☉ and a mass-to-light ratio of 2.05±0.04 in the V band. It has a projected ellipticity of 0.01, meaning is it essentially spherical. The density profile of the cluster members suggests it has not yet undergone core collapse. It has a core radius of 1.3 ly (0.39 pc), a half-mass radius of 9.6 ly (2.95 pc), and a half-light radius of 6.0 ly (1.83 pc). The stellar density at the core is 5.13 M☉ per cubic parsec. It has a tidal radius of 59 ly (18.0 pc).The cluster shows at least two distinct populations of stars, which most likely represent two separate episodes of star formation. Of the main sequence stars in the cluster, 79%±1% are from the first generation and 21%±1% from the second. The second generation is polluted by materials released by the first. In particular, the abundances of helium, carbon, magnesium, aluminium, and sodium differ between the two populations.Indications are this is an Oosterhoff type I, or "metal-rich" system. A 2010 study identified 245 variable stars in the cluster's field, of which 209 are RR Lyrae variables, four are Type II Cepheids, 25 are long period variables, and one is an eclipsing binary. The cluster may prove to be the galaxy's richest in terms of RR Lyrae variables. It has six binary millisecond pulsars, including one (COM6266B) that is displaying eclipsing behavior from gas streaming off its companion. There are multiple X-ray sources, including 50 within the half-mass radius. 47 blue straggler candidates have been identified, formed from the merger of two stars in a binary system, and these are preferentially concentrated near the core region.It is hypothesized that this cluster may be host to an intermediate mass black hole (IMBH), and it is considered particularly suitable for searching for such an object. Examination of the proper motion of stars within 17″ of the core does not require an IMBH to explain. However, simulations can not rule out an IMBH with a mass of a few thousand M☉. Based upon radial velocity measurements within an arcsecond of the core, Kiselev et al. (2008) made the claim that there is an IMBH with a mass in the range (1–9)×103 M☉.NGC 1313
NGC 1313 (also known as the Topsy Turvy Galaxy) is a field galaxy and a barred spiral galaxy discovered by the Scottish astronomer James Dunlop on 27 September 1826. It has a diameter of about 50,000 light-years, or about half the size of the Milky Way.NGC 1313 lies within the Virgo Supercluster.NGC 2276
NGC 2276 is an intermediate spiral galaxy in the constellation Cepheus. The galaxy lies 105 million light-years away from Earth. NGC 2276 has an asymmetrical appearance, most likely caused by gravitational interactions with its neighbor, elliptical galaxy NGC 2300. One of the many starburst spiral arms contains an intermediate mass black hole with 50,000 times the mass of the Sun, named NGC 2276-3c. NGC 2276-3c has produced two jets: a large-scale radio jet, approximately 2,000 light years long, and an "inner jet" about 6 light years long. The galaxy shows an enhanced rate of star formation that may have been triggered by a collision with a dwarf galaxy, or by the gravitational interaction with its neighbor compressing gas and dust.
It was discovered by Friedrich August Theodor Winnecke in 1876. In the Atlas of Peculiar Galaxies, the galaxy is mentioned twice, once as Arp 25, in the category spiral galaxies with one heavy arm, and one more time as Arp 114, in the category elliptical galaxies close to and perturbing spiral galaxies, in pair with NGC 2300.
NGC 2276 has been home to six supernovae in the last 60 years; SN 1962Q (mag 16.9), SN 1968V (mag 15.7), SN 1968W (mag 16.6), SN 1993X (type II, mag. 16.3), SN 2005dl (type II, mag. 17.1) and SN 2016gfy (type II, mag 16.3).NGC 4395
NGC 4395 is a low surface brightness spiral galaxy with a halo that is about 8′ in diameter. It has several wide areas of greater brightness running northwest to southeast. The one furthest southeast is the brightest. Three of the patches have their own NGC numbers: 4401, 4400, and 4399 running east to west.
The nucleus of NGC 4395 is active and the galaxy is classified as a Seyfert. It is notable for containing one of the smallest supermassive black hole with an accurately-determined mass. The central black hole has a mass of "only" 300,000 Sun masses, which would make it a so-called "intermediate-mass black hole".NGC 5286
NGC 5286 (also known as Caldwell 84) is a globular cluster of stars located some 35,900 light years away in the constellation Centaurus. At this distance, the light from the cluster has undergone reddening from interstellar gas and dust equal to E(B – V) = 0.24 magnitude in the UBV photometric system. The cluster lies 4 arc-minutes north of the naked-eye star M Centauri. It was discovered by Scottish astronomer James Dunlop, active in Australia, and listed in his 1827 catalog.This cluster is about 29 kly (8.9 kpc) from the Galactic Center and is currently orbiting in the Milky Way halo. It may be associated with the Monoceros Ring—a long tidal stream of stars that could have been formed from a disrupted dwarf galaxy. NGC 5286 may be one of the oldest globular clusters in the galaxy, with an estimated age of 12.54 billion years. It is not perfectly spherical, but has a projected ellipticity of 0.12.The velocity dispersion of stars at the center of the cluster is (8.1 ± 1.0) km/s. Based upon the motions of stars at the core of this cluster, it may host an intermediate mass black hole with less than 1% of the cluster's mass. The upper limit for the mass estimate of this object is 6,000 times the mass of the Sun.NGC 5286 is part of the Gaia Sausage, the hypothesised remains of a merged dwarf galaxy.Omega Centauri
Omega Centauri (ω Cen or NGC 5139) is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 15,800 light-years (4,850 pc), it is the largest globular cluster in the Milky Way at a diameter of roughly 150 light-years. It is estimated to contain approximately 10 million stars and a total mass equivalent to 4 million solar masses.Omega Centauri is so distinctive from the other galactic globular clusters that it is thought to have an alternate origin as the core remnant of a disrupted dwarf galaxy.Rossi X-ray Timing Explorer
The Rossi X-ray Timing Explorer (RXTE) was a satellite that observed the time variation of astronomical X-ray sources, named after physicist Bruno Rossi. The RXTE had three instruments—an All Sky Monitor, the Proportional Counter Array, and the High-Energy X-ray Timing Experiment (HEXTE). The RXTE observed X-rays from black holes, neutron stars, X-ray pulsars and X-ray bursts. It was funded as part of the Explorer program, and is sometimes also called Explorer 69.
RXTE had a mass of 3200 kg and was launched from Cape Canaveral on 30 December 1995 on a Delta rocket. Its International Designator is 1995-074A.
Observations from the Rossi X-ray Timing Explorer have been used as evidence for the existence of the frame-dragging effect predicted by the theory of general relativity. RXTE results have, as of late 2007, been used in more than 1400 scientific papers.
In January 2006, it was announced that Rossi had been used to locate a candidate intermediate-mass black hole named M82 X-1. In February 2006, data from RXTE was used to prove that the diffuse background X-ray glow in our galaxy comes from innumerable, previously undetected white dwarfs and from other stars' coronae. In April 2008, RXTE data was used to infer the size of the smallest known black hole.RXTE ceased science operations on 3 January 2012.NASA scientists said that the decommissioned RXTE would re-enter the Earth's atmosphere "between 2014 and 2023". Later it became clear that the satellite would re-enter in late April or early May 2018, and the spacecraft fell out of orbit on April 30, 2018.Stellar collision
A stellar collision is the coming together of two stars caused by gravity, gravitational radiation, or other mechanisms not well understood. Astronomers predict that events of this type occur in the globular clusters of our galaxy about once every 10,000 years. On 2 September 2008 scientists first observed a stellar merger in Scorpius (named V1309 Scorpii), though it was not known to be the result of a stellar merger at the time. A series of stellar collisions in a dense cluster over a short period of time can lead to an intermediate-mass black hole via "runaway stellar collisions".Any stars in the universe can collide, whether they are 'alive', meaning fusion is still active in the star, or 'dead', with fusion no longer taking place. White dwarf stars, neutron stars, black holes, main sequence stars, giant stars, and supergiants are very different in type, mass, temperature, and radius, and so react differently.A gravitational wave event that occurred on 25 August 2017, GW170817, was reported on 16 October 2017 to be associated with the merger of two neutron stars in a distant galaxy, the first such merger to be observed via gravitational radiation.Ultraluminous X-ray source
An ultraluminous X-ray source (ULX) is an astronomical source of X-rays that is less luminous than an active galactic nucleus but is more consistently luminous than any known stellar process (over 1039 erg/s, or 1032 watts), assuming that it radiates isotropically (the same in all directions). Typically there is about one ULX per galaxy in galaxies which host them, but some galaxies contain many. The Milky Way has not been shown to contain a ULX. The main interest in ULXs stems from their luminosity exceeding the Eddington luminosity of neutron stars and even stellar black holes. It is not known what powers ULXs; models include beamed emission of stellar mass objects, accreting intermediate-mass black holes, and super-Eddington emission.X1
X1 or X-1 may refer to:
VehiclesBell X-1, the first aircraft to exceed the speed of sound in controlled level flight
BMW X1, a BMW Compact Sports Activity Vehicle
HM Submarine X1, a Royal Navy submarine
McLaren X-1, a 2012 bespoke supercar created for an anonymous client and based on the McLaren MP4-12C
Red Bull X1, the former name of the Red Bull X2010, a fictional car created for the game Gran Turismo 5
SL X1, a former Swedish commuter train
Sinclair X-1, an electrically assisted faired recumbent bicycle
Wrightspeed X1, an electric sports car based on the Ariel Atom chassis
X-1 Submarine, the United States Navy's only midget submarine
X1 (dinghy), a fast, light-weight sailing dinghy designed for inland racing
XS-1 (spacecraft), a space plane in development
Yamaha X-1 and X-1R, related Yamaha underbone motorcyclesComputingX1 (computer), a Japanese home computer manufactured by the Sharp Corporation
Xbox One, a video game console
a one-lane PCI Express slot
Cray X1, a supercomputer sold since 2003
Electrologica X1, an early Dutch computer
ThinkPad X1 Carbon, a high-end notebook computer released by Lenovo in 2012
X1 (software company) formerly known as X1 Technologies, Inc.
Tegra X1, a system on a chip released by Nvidia in 2015OtherX1 (New York City bus)
X1, a Metrobus route
X Minus One, an old time radio show
x −1, the multiplicative inverse of x (another way to denote 1⁄x, one divided by x)
Cygnus X-1 and Scorpius X-1, two astronomical x-ray sources
M82 X-1, a candidate intermediate-mass black hole detected in January 2006
Sony Ericsson XPERIA X1, a mobile phone
Excel X1, a bus route from Lowestoft to Peterborough in Eastern England
X1 Steel Link, a bus rapid transit service between Sheffield, Rotherham and Maltby in northern England
United States patent X1, by Samuel Hopkins (inventor)
X-Men, the first film in the X-Men franchise
X1 (Egyptian hieroglyph t), an extremely common alphabetic letter in the Ancient Egyptian alphabet