Supermassive black hole#Formation

Supermassive black holes are classically defined as black holes with a mass above 100,000 ({{val|e=5}}) solar masses ({{Solar mass|link=y}}); some have masses of {{solar mass|several billion}}.{{Cite web|title=Black Hole {{!}} COSMOS|url=https://astronomy.swin.edu.au/cosmos/B/Black+Hole|access-date=2020-08-29|website=astronomy.swin.edu.au}} Supermassive black holes have physical properties that clearly distinguish them from lower-mass classifications. First, the tidal forces in the vicinity of the event horizon are significantly weaker for supermassive black holes. The tidal force on a body at a black hole's event horizon is inversely proportional to the square of the black hole's mass:{{citation|last1=Kutner|first1=Marc L.|title=Astronomy: A Physical Perspective|url=https://books.google.com/books?id=2QVmiMW0O0MC&pg=PA149|page=149|year=2003|publisher=Cambridge University Press|isbn=978-0521529273}} a person at the event horizon of a {{Solar mass|10 million}} black hole experiences about the same tidal force between their head and feet as a person on the surface of the Earth. Unlike with stellar-mass black holes, one would not experience significant tidal force until very deep into the black hole's event horizon.{{citation|title=Problem 138: The Intense Gravity of a Black Hole|url=https://spacemath.gsfc.nasa.gov/blackholes.html|work=Space Math @ NASA: Mathematics Problems about Black Holes|publisher=NASA|access-date=December 4, 2018}}

It is somewhat counterintuitive to note that the average density of a SMBH within its event horizon (defined as the mass of the black hole divided by the volume of space within its Schwarzschild radius) can be smaller than the density of water.{{Cite journal|last1=Celotti |first1=A. |last2=Miller |first2=J.C. |last3=Sciama |first3=D.W. |title= Astrophysical evidence for the existence of black holes |date=1999|pages=A3–A21|issue=12A |journal=Class. Quantum Grav. |volume=16 |arxiv=astro-ph/9912186 |doi = 10.1088/0264-9381/16/12A/301|url=https://cds.cern.ch/record/411555 |type=Submitted manuscript |bibcode=1999CQGra..16A...3C |s2cid=17677758 }} This is because the Schwarzschild radius ($r\_\backslash text\{s\}$) is directly proportional to its mass. Since the volume of a spherical object (such as the event horizon of a non-rotating black hole) is directly proportional to the cube of the radius, the density of a black hole is inversely proportional to the square of the mass, and thus higher mass black holes have a lower average density.{{citation | title=Exploring The Invisible Universe: From Black Holes To Superstrings | first1=Baaquie Belal | last1=Ehsan | first2=Willeboordse Frederick | last2=Hans | publisher=World Scientific | year=2015 | isbn=978-9814618694 | page=200 | url=https://books.google.com/books?id=1Ri3CgAAQBAJ&pg=PA200 | bibcode=2015eiub.book.....B }}

The Schwarzschild radius of the event horizon of a nonrotating and uncharged supermassive black hole of around {{Solar mass|1 billion}} is comparable to the semi-major axis of the orbit of planet Uranus, which is about 19 AU.{{Cite web|title=Uranus Fact Sheet|url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html|access-date=2020-08-29|website=nssdc.gsfc.nasa.gov}}{{Cite web|title=Black Hole Calculator – Fabio Pacucci (Harvard University & SAO)|url=https://www.fabiopacucci.com/resources/black-hole-calculator/|access-date=2020-08-29|website=Fabio Pacucci}} Some astronomers refer to black holes of greater than {{Solar mass|5 billion}} as ultramassive black holes (UMBHs or UBHs),{{cite journal|arxiv=0808.2813|doi=10.1111/j.1365-2966.2008.13864.x |title=Is there an upper limit to black hole masses? |year=2009 |last1=Natarajan |first1=Priyamvada |last2=Treister |first2=Ezequiel |journal=Monthly Notices of the Royal Astronomical Society |volume=393 |issue=3 |pages=838–845 |doi-access=free |bibcode=2009MNRAS.393..838N |s2cid=6568320 }} but the term is not broadly used. Possible examples include the black holes at the cores of TON 618, NGC 6166, ESO 444-46 and NGC 4889,{{Cite web |title=Massive Black Holes Dwell in Most Galaxies, According to Hubble Census |url=http://hubblesite.org/contents/news-releases/1997/news-1997-01 |access-date=2022-08-21 |website=HubbleSite.org |language=en}} which are among the most massive black holes known.

Some studies have suggested that the maximum natural mass that a black hole can reach, while being luminous accretors (featuring an accretion disk), is typically on the order of about {{Solar mass|50 billion}}.{{Cite journal|last=King|first=Andrew|date=2016|title=How big can a black hole grow?|bibcode=2016MNRAS.456L.109K|journal=Monthly Notices of the Royal Astronomical Society|volume=456|issue=1|pages=L109–L112|doi=10.1093/mnrasl/slv186|doi-access=free |arxiv=1511.08502|s2cid=40147275}}{{Cite journal|last1=Inayoshi|first1=Kohei|last2=Haiman|first2=Zoltán|date=2016-09-12|title=Is There a Maximum Mass for Black Holes in Galactic Nuclei?|bibcode= 2016ApJ...828..110I |arxiv=1601.02611|journal=The Astrophysical Journal|volume=828|issue=2|pages=110|doi=10.3847/0004-637X/828/2/110|s2cid=118702101 |doi-access=free }} However, a 2020 study suggested even larger black holes, dubbed Stupendously large black holes (SLABs), with masses greater than {{Solar mass|100 billion}}, could exist based on used models; some studies place the black hole at the core of Phoenix A in this category.{{Cite web|last=September 2020|first=Charles Q. Choi 18|title='Stupendously large' black holes could grow to truly monstrous sizes|url=https://www.space.com/black-holes-can-reach-stupendously-large-sizes.html|access-date=2021-03-10|website=Space.com|date=September 18, 2020|language=en}}

The story of how supermassive black holes were found began with the investigation by Maarten Schmidt of the radio source 3C 273 in 1963. Initially this was thought to be a star, but the spectrum proved puzzling. It was determined to be hydrogen emission lines that had been redshifted, indicating the object was moving away from the Earth.{{cite conference | title=3C 273: A Star-like Object with Large Red-Shift | last1=Schmidt | first1=Maarten | conference=Quasi-Stellar Sources and Gravitational Collapse: Proceedings of the 1st Texas Symposium on Relativistic Astrophysics | journal=Quasi-Stellar Sources and Gravitational Collapse |location=Chicago |publisher=University of Chicago Press| editor1-first=Ivor | editor1-last=Robinson | editor2-first=Alfred | editor2-last=Schild | editor3-first=E.L. | editor3-last=Schucking | year=1965 | page=455 | bibcode=1965qssg.conf..455S |mode=cs2}} Hubble's law showed that the object was located several billion light-years away, and thus must be emitting the energy equivalent of hundreds of galaxies. The rate of light variations of the source dubbed a quasi-stellar object, or quasar, suggested the emitting region had a diameter of one parsec or less. Four such sources had been identified by 1964.{{cite journal | title=The Quasi-Stellar Radio Sources 3C 48 and 3C 273 | last1=Greenstein | first1=Jesse L. | last2=Schmidt | first2=Maarten | journal=Astrophysical Journal | volume=140 | page=1 | date=July 1, 1964 | doi=10.1086/147889 | bibcode=1964ApJ...140....1G | s2cid=123147304 |mode=cs2| doi-access=free }}

In 1963, Fred Hoyle and W. A. Fowler proposed the existence of hydrogen-burning supermassive stars (SMS) as an explanation for the compact dimensions and high energy output of quasars. These would have a mass of about {{nowrap|{{val|e=5}}–{{val|e=9|u={{solar mass}}}}}}. However, Richard Feynman noted stars above a certain critical mass are dynamically unstable and would collapse into a black hole, at least if they were non-rotating.{{cite book | title=Feynman Lectures on Gravitation | first1=Richard | last1=Feynman | publisher=CRC Press | year=2018 | isbn=978-0429982484 | page=12 | url=https://books.google.com/books?id=AEtnDwAAQBAJ&pg=PT12 |mode=cs2}} Fowler then proposed that these supermassive stars would undergo a series of collapse and explosion oscillations, thereby explaining the energy output pattern. Appenzeller and Fricke (1972) built models of this behavior, but found that the resulting star would still undergo collapse, concluding that a non-rotating {{val|0.75|e=6|u=solar mass}} SMS "cannot escape collapse to a black hole by burning its hydrogen through the CNO cycle".{{cite journal | title=Hydrodynamic Model Calculations for Supermassive Stars I. The Collapse of a Nonrotating 0.75×10⁶{{solar mass}} Star | last1=Appenzeller | first1=I. | last2=Fricke | first2=K. | journal=Astronomy and Astrophysics | volume=18 | page=10 | date=April 1972 | bibcode=1972A&A....18...10A |mode=cs2}}

Edwin E. Salpeter and Yakov Zeldovich made the proposal in 1964 that matter falling onto a massive compact object would explain the properties of quasars. It would require a mass of around {{val|e=8|u={{solar mass}}}} to match the output of these objects. Donald Lynden-Bell noted in 1969 that the infalling gas would form a flat disk that spirals into the central "Schwarzschild throat". He noted that the relatively low output of nearby galactic cores implied these were old, inactive quasars.{{cite book | title=Astrophysical Formulae: Space, Time, Matter and Cosmology | series=Astronomy and Astrophysics Library | first1=Kenneth R. | last1=Lang | edition=3 | publisher=Springer | year=2013 | isbn=978-3662216392 | page=217 | url=https://books.google.com/books?id=Nq_1CAAAQBAJ&pg=PA217 |mode=cs2}} Meanwhile, in 1967, Martin Ryle and Malcolm Longair suggested that nearly all sources of extra-galactic radio emission could be explained by a model in which particles are ejected from galaxies at relativistic velocities, meaning they are moving near the speed of light.{{cite journal | title=A possible method for investigating the evolution of radio galaxies | last1=Ryle | first1=Martin, Sir | last2=Longair | first2=M. S. | journal=Monthly Notices of the Royal Astronomical Society | volume=136 | issue=2 | page=123 | year=1967 | doi=10.1093/mnras/136.2.123 | bibcode=1967MNRAS.136..123R | doi-access= free|mode=cs2}} Martin Ryle, Malcolm Longair, and Peter Scheuer then proposed in 1973 that the compact central nucleus could be the original energy source for these relativistic jets.

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 {{val|e=10|u={{solar mass}}}}, or a large number of smaller black holes with masses below {{val|e=3|u={{solar mass}}}}.{{cite journal | title=Black Holes in Elliptical Galaxies | last1=Wolfe | first1=A. M. | last2=Burbidge | first2=G. R. | journal=Astrophysical Journal | volume=161 | page=419 | date=August 1970 | doi=10.1086/150549 | bibcode=1970ApJ...161..419W |mode=cs2| doi-access= }} Dynamical evidence for a massive dark object was found at the core of the active elliptical galaxy Messier 87 in 1978, initially estimated at {{Val|5e9|u=solar mass}}.{{cite journal | title=Dynamical evidence for a central mass concentration in the galaxy M87 | last1=Sargent | first1=W. L. W. | last2=Young | first2=P. J. | last3=Boksenberg | first3=A. | last4=Shortridge | first4=K. | last5=Lynds | first5=C. R. | last6=Hartwick | first6=F. D. A. | display-authors=1 | journal=Astrophysical Journal, Part 1 | volume=221 | date=May 1, 1978 | pages=731–744 | doi=10.1086/156077 | bibcode=1978ApJ...221..731S |mode=cs2| doi-access=free }} Discovery of similar behavior in other galaxies soon followed, including the Andromeda Galaxy in 1984 and the Sombrero Galaxy in 1988.

Donald Lynden-Bell and Martin Rees hypothesized in 1971 that the center of the Milky Way galaxy would contain a massive black hole.{{cite book | title=How does the Galaxy work?: A Galactic Tertulia with Don Cox and Ron Reynolds | last1=Schödel | first1=R. | last2=Genzel | first2=R. | volume=315 | series=Astrophysics and Space Science Library | editor1-first=Emilio Javier | editor1-last=Alfaro | editor2-first=Enrique | editor2-last=Perez | editor3-first=José | editor3-last=Franco | publisher=Springer Science & Business Media | year=2006 | isbn=978-1402026201 | page=201 | url=https://books.google.com/books?id=Hk9UZsgBfM4C&pg=PA201 |mode=cs2}} Sagittarius A* was discovered and named on February 13 and 15, 1974, by astronomers Bruce Balick and Robert Brown using the Green Bank Interferometer of the National Radio Astronomy Observatory.{{cite book | author=Fulvio Melia | title=The Galactic Supermassive Black Hole | publisher=Princeton University Press | date=2007 | isbn =978-0-691-13129-0 |page=2 |mode=cs2}} They discovered a radio source that emits synchrotron radiation; it was found to be dense and immobile because of its gravitation. This was, therefore, the first indication that a supermassive black hole exists in the center of the Milky Way.

The Hubble Space Telescope, launched in 1990, provided the resolution needed to perform more refined observations of galactic nuclei. In 1994 the Faint Object Spectrograph on the Hubble was used to observe Messier 87, finding that ionized gas was orbiting the central part of the nucleus at a velocity of ±500 km/s. The data indicated a concentrated mass of {{Val|2.4|0.7|e=9|u=solar mass}} lay within a {{Val|0.25|ul=arcsecond}} span, providing strong evidence of a supermassive black hole.{{cite journal | title=HST FOS spectroscopy of M87: Evidence for a disk of ionized gas around a massive black hole | last1=Harms | first1=Richard J. | last2=Ford | first2=Holland C. | last3=Tsvetanov | first3=Zlatan I. | last4=Hartig | first4=George F. | last5=Dressel | first5=Linda L. | last6=Kriss | first6=Gerard A. | last7=Bohlin | first7=Ralph | last8=Davidsen | first8=Arthur F. | last9=Margon | first9=Bruce | last10=Kochhar | first10=Ajay K. | display-authors=1 | journal=Astrophysical Journal, Part 2 | volume=435 | issue=1 | pages=L35–L38 | date=November 1994 | doi=10.1086/187588 | bibcode=1994ApJ...435L..35H |mode=cs2| doi-access=free }}

Using the Very Long Baseline Array to observe Messier 106, Miyoshi et al. (1995) were able to demonstrate that the emission from an H₂O maser in this galaxy came from a gaseous disk in the nucleus that orbited a concentrated mass of {{Val|3.6|e=7|u=solar mass}}, which was constrained to a radius of 0.13 parsecs. Their ground-breaking research noted that a swarm of solar mass black holes within a radius this small would not survive for long without undergoing collisions, making a supermassive black hole the sole viable candidate.{{cite journal | title=Evidence for a black hole from high rotation velocities in a sub-parsec region of NGC4258 | last1=Miyoshi | first1=Makoto | last2=Moran | first2=James | last3=Herrnstein | first3=James | last4=Greenhill | first4=Lincoln | last5=Nakai | first5=Naomasa | last6=Diamond | first6=Philip | last7=Inoue | first7=Makoto | display-authors=1 | journal=Nature | volume=373 | issue=6510 | pages=127–129 | date=January 1995 | doi=10.1038/373127a0 | bibcode=1995Natur.373..127M | s2cid=4336316 |mode=cs2}} Accompanying this observation which provided the first confirmation of supermassive black holes was the discovery{{cite journal| title=Gravitationally redshifted emission implying an accretion disk and massive black hole in the active galaxy MCG-6-30-15 |journal= Nature |date=1995 | volume=375 | issue=6533 | pages=659–661 |last1=Tanaka |first1=Y. | last2=Nandra| first2=K. | last3=Fabian| first3=A. C. |doi= 10.1038/375659a0 | bibcode=1995Natur.375..659T |s2cid= 4348405 |mode=cs2}} of the highly broadened, ionised iron Kα emission line (6.4 keV) from the galaxy MCG-6-30-15. The broadening was due to the gravitational redshift of the light as it escaped from just 3 to 10 Schwarzschild radii from the black hole.

On April 10, 2019, the Event Horizon Telescope Collaboration released the first horizon-scale image of a black hole, in the center of the galaxy Messier 87. In March 2020, astronomers suggested that additional subrings should form the photon ring, proposing a way of better detecting these signatures in the first black hole image.{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Infinite Visions Were Hiding in the First Black Hole Image's Rings |url=https://www.nytimes.com/2020/03/28/science/black-hole-rings.html |date=28 March 2020 |work=The New York Times |access-date=29 March 2020 |mode=cs2}}{{cite journal |last=Johnson |first=Michael D. |display-authors=etal |title=Universal interferometric signatures of a black hole's photon ring |date=18 March 2020 |journal=Science Advances |volume=6 |issue=12, eaaz1310 |doi=10.1126/sciadv.aaz1310 |doi-access=free |page=eaaz1310 |pmid=32206723 |pmc=7080443 |arxiv=1907.04329 |bibcode=2020SciA....6.1310J |mode=cs2}}

File:Artist impression of a supermassive black hole at the centre of a galaxy.jpg.]]

The origin of supermassive black holes remains an active field of research. Astrophysicists agree that black holes can grow by accretion of matter and by merging with other black holes.{{Cite journal|last1=Kulier|first1=Andrea|last2=Ostriker|first2=Jeremiah P.|last3=Natarajan|first3=Priyamvada|last4=Lackner|first4=Claire N.|last5=Cen|first5=Renyue|date=2015-02-01|title=Understanding Black Hole Mass Assembly via Accretion and Mergers at Late Times in Cosmological Simulations|bibcode=2015ApJ...799..178K|journal=The Astrophysical Journal|volume=799|issue=2|pages=178|doi=10.1088/0004-637X/799/2/178|arxiv=1307.3684|s2cid=118497238}}{{Cite journal|last1=Pacucci|first1=Fabio|last2=Loeb|first2=Abraham|date=2020-06-01|title=Separating Accretion and Mergers in the Cosmic Growth of Black Holes with X-Ray and Gravitational-wave Observations|bibcode=2020ApJ...895...95P|journal=The Astrophysical Journal|volume=895|issue=2|pages=95|doi=10.3847/1538-4357/ab886e|arxiv=2004.07246|s2cid=215786268 |doi-access=free }} There are several hypotheses for the formation mechanisms and initial masses of the progenitors, or "seeds", of supermassive black holes. Independently of the specific formation channel for the black hole seed, given sufficient mass nearby, it could accrete to become an intermediate-mass black hole and possibly a SMBH if the accretion rate persists.

Distant and early supermassive black holes, such as J0313–1806,{{cite web|title=Researchers discover the earliest supermassive black hole and quasar in the universe|author=Harrison Tasoff|website=phys.org|date=January 19, 2021|url=https://phys.org/news/2021-01-earliest-supermassive-black-hole-quasar.html|quote=The presence of such a massive black hole so early in the universe's history challenges theories of black hole formation. As lead author [Feige] Wang, now a NASA Hubble fellow at the University of Arizona, explains: 'Black holes created by the very first massive stars could not have grown this large in only a few hundred million years.'}} and ULAS J1342+0928,{{cite web |last1=Landau |first1=Elizabeth |last2=Bañados |first2=Eduardo |title=Found: Most Distant Black Hole |url=https://www.jpl.nasa.gov/news/news.php?feature=7017 |date=December 6, 2017 |work=NASA |access-date=December 6, 2017 | quote='This black hole grew far larger than we expected in only 690 million years after the Big Bang, which challenges our theories about how black holes form,' said study co-author Daniel Stern of NASA's Jet Propulsion Laboratory in Pasadena, California.}} are hard to explain so soon after the Big Bang. Some postulate they might come from direct collapse of dark matter with self-interaction.{{cite journal| title=Gravothermal Collapse of Self-Interacting Dark Matter Halos and the Origin of Massive Black Holes |journal=Physical Review Letters|date=2002 | volume=88 | page=101301 |last1= Balberg |first1= Shmuel | last2= Shapiro | first2= Stuart L. |issue=10|doi=10.1103/PhysRevLett.88.101301|arxiv=astro-ph/0111176 |pmid=11909338| bibcode=2002PhRvL..88j1301B|s2cid=20557031|url=https://cds.cern.ch/record/526111}}{{cite journal| title=Supermassive Black Holes from Ultra-Strongly Self-Interacting Dark Matter |journal=The Astrophysical Journal |date=2015 | volume=804 | page=131 |last1= Pollack |first1= Jason | last2= Spergel | first2= David N. | last3= Steinhardt | first3= Paul J.|issue=2|doi=10.1088/0004-637X/804/2/131 | arxiv=1501.00017|bibcode=2015ApJ...804..131P |s2cid=15916893 }}{{cite journal| title=Seeding Supermassive Black Holes with Self-interacting Dark Matter: A Unified Scenario with Baryons |journal=The Astrophysical Journal Letters |date=2021 | volume=914 | page=L26 |last1= Feng |first1= W.-X. | last2= Yu | first2= H.-B. | last3= Zhong | first3= Y.-M. |issue=2|doi=10.3847/2041-8213/ac04b0 | arxiv=2010.15132|bibcode=2021ApJ...914L..26F |s2cid=225103030 |doi-access=free }} A small minority of sources argue that they may be evidence that the Universe is the result of a Big Bounce, instead of a Big Bang, with these supermassive black holes being formed before the Big Bounce.{{cite web |url=http://www.news.com.au/technology/science/space/black-hole-at-the-dawn-of-time-challenges-our-understanding-of-how-the-universe-was-formed/news-story/3279356705a47d45416ae2e6ead41175|title=Black hole at the dawn of time challenges our understanding of how the universe was formed|author=Seidel, Jamie |date=December 7, 2017|access-date=December 9, 2017|publisher=News Corp Australia |quote=It had reached its size just 690 million years after the point beyond which there is nothing. The most dominant scientific theory of recent years describes that point as the Big Bang—a spontaneous eruption of reality as we know it out of a quantum singularity. But another idea has recently been gaining weight: that the universe goes through periodic expansions and contractions—resulting in a 'Big Bounce'. And the existence of early black holes has been predicted to be a key telltale as to whether or not the idea may be valid. This one is very big. To get to its size—800 million times more mass than our Sun—it must have swallowed a lot of stuff. ... As far as we understand it, the universe simply wasn't old enough at that time to generate such a monster.}}{{cite web |url=http://www.youmagazine.gr/2017/12/23256-mia-mavri-trypa-arhaioteri-apo-to-sympan-video/|title=A Black Hole that is more ancient than the Universe|date=December 8, 2017|access-date=December 9, 2017|publisher=You Magazine (Greece) |language=el |quote=This new theory that accepts that the Universe is going through periodic expansions and contractions is called 'Big Bounce'}}

{{Main|Population III star|Quasi-star|Dark star (dark matter)}}

{{Update|section|date=November 2022}}

The early progenitor seeds may be black holes of {{Solar mass|tens or perhaps hundreds of}} that are left behind by the explosions of massive stars and grow by accretion of matter. Another model involves a dense stellar cluster undergoing core collapse as the negative heat capacity of the system drives the velocity dispersion in the core to relativistic speeds.{{cite book |last=Spitzer |first=L. |author-link= Lyman Spitzer|publisher=Princeton University Press |date=1987 |title=Dynamical Evolution of Globular Clusters |isbn=978-0-691-08309-4}}{{Cite journal|last1=Boekholt|first1=T. C. N.|last2=Schleicher|first2=D. R. G.|last3=Fellhauer|first3=M.|last4=Klessen|first4=R. S.|last5=Reinoso|first5=B.|last6=Stutz|first6=A. M.|last7=Haemmerlé|first7=L.|date=2018-05-01|title=Formation of massive seed black holes via collisions and accretion|bibcode=2018MNRAS.476..366B|journal=Monthly Notices of the Royal Astronomical Society|volume=476|issue=1|pages=366–380|doi=10.1093/mnras/sty208|doi-access=free |arxiv=1801.05841|s2cid=55411455}}

Before the first stars, large gas clouds could collapse into a "quasi-star", which would in turn collapse into a black hole of around {{Solar mass|20}}.{{cite journal|last=Begelman|first=M. C.|display-authors=etal|date=Jun 2006|title=Formation of supermassive black holes by direct collapse in pre-galactic haloed|journal=Monthly Notices of the Royal Astronomical Society|volume=370|issue=1|pages=289–298|arxiv=astro-ph/0602363|bibcode=2006MNRAS.370..289B|doi=10.1111/j.1365-2966.2006.10467.x|doi-access=free |s2cid=14545390}} These stars may have also been formed by dark matter halos drawing in enormous amounts of gas by gravity, which would then produce supermassive stars with {{Solar mass|tens of thousands of}}.{{cite web|url=https://www.scientificamerican.com/article/zeroing-in-on-how-supermassive-black-holes-formed1/|title=Zeroing In on How Supermassive Black Holes Formed|last=Saplakoglu |first=Yasemin |work=Scientific American|date=September 29, 2017|access-date=April 8, 2019}}{{cite web|url=http://www.astronomy.com/news/2017/11/cooking-up-supermassive-black-holes|title=Cooking up supermassive black holes in the early universe|last=Johnson-Goh |first=Mara |website=Astronomy|date=November 20, 2017|access-date=April 8, 2019}} The "quasi-star" becomes unstable to radial perturbations because of electron-positron pair production in its core and could collapse directly into a black hole without a supernova explosion (which would eject most of its mass, preventing the black hole from growing as fast). A 2018 theory proposes that SMBH seeds were formed in the very early universe each from the collapse of a supermassive star with mass of around {{Solar mass|100,000}}.{{cite journal|url=https://www.accessscience.com/content/supermassive-star/669400|title=Supermassive star|journal=Access Science |year=2018 |doi=10.1036/1097-8542.669400 |last1=Pasachoff |first1=Jay M. }}

Large, high-redshift clouds of metal-free gas,{{Cite journal|last1=Yue|first1=Bin|last2=Ferrara|first2=Andrea|last3=Salvaterra|first3=Ruben|last4=Xu|first4=Yidong|last5=Chen|first5=Xuelei|date=2014-05-01|title=The brief era of direct collapse black hole formation|bibcode=2014MNRAS.440.1263Y|journal=Monthly Notices of the Royal Astronomical Society|volume=440|issue=2|pages=1263–1273|doi=10.1093/mnras/stu351|doi-access=free |arxiv=1402.5675|s2cid=119275449}} when irradiated by a sufficiently intense flux of Lyman–Werner photons,{{Cite journal|last1=Sugimura|first1=Kazuyuki|last2=Omukai|first2=Kazuyuki|last3=Inoue|first3=Akio K.|date=2014-11-01|title=The critical radiation intensity for direct collapse black hole formation: dependence on the radiation spectral shape|bibcode=2014MNRAS.445..544S|journal=Monthly Notices of the Royal Astronomical Society|volume=445|issue=1|pages=544–553|doi=10.1093/mnras/stu1778|doi-access=free |arxiv=1407.4039|s2cid=119257740}} can avoid cooling and fragmenting, thus collapsing as a single object due to self-gravitation.{{Cite journal|last1=Bromm|first1=Volker|last2=Loeb|first2=Abraham|date=2003-10-01|title=Formation of the First Supermassive Black Holes|bibcode=2003ApJ...596...34B|journal=The Astrophysical Journal|volume=596|issue=1|pages=34–46|doi=10.1086/377529|arxiv=astro-ph/0212400|s2cid=14419385}}{{Cite web|last=Siegel|first=Ethan|title='Direct Collapse' Black Holes May Explain Our Universe's Mysterious Quasars|url=https://www.forbes.com/sites/startswithabang/2017/12/26/direct-collapse-black-holes-may-explain-our-universes-mysterious-quasars/|access-date=2020-08-28|website=Forbes}} The core of the collapsing object reaches extremely large values of matter density, of the order of about {{val|e=7|u=g|up=cm3}}, and triggers a general relativistic instability.{{Cite journal|last1=Montero|first1=Pedro J.|last2=Janka|first2=Hans-Thomas|last3=Müller|first3=Ewald|date=2012-04-01|title=Relativistic Collapse and Explosion of Rotating Supermassive Stars with Thermonuclear Effects|bibcode=2012ApJ...749...37M|journal=The Astrophysical Journal|volume=749|issue=1|pages=37|doi=10.1088/0004-637X/749/1/37|arxiv=1108.3090|s2cid=119098587}} Thus, the object collapses directly into a black hole, without passing from the intermediate phase of a star, or of a quasi-star. These objects have a typical mass of about {{Solar mass|100,000}} and are named direct collapse black holes.{{Cite journal|last1=Habouzit|first1=Mélanie|last2=Volonteri|first2=Marta|author2-link=Marta Volonteri|last3=Latif|first3=Muhammad|last4=Dubois|first4=Yohan|last5=Peirani|first5=Sébastien|date=2016-11-01|title=On the number density of 'direct collapse' black hole seeds|bibcode=2016MNRAS.463..529H|journal=Monthly Notices of the Royal Astronomical Society|volume=463|issue=1|pages=529–540|doi=10.1093/mnras/stw1924|doi-access=free |arxiv=1601.00557|s2cid=118409029}}

A 2022 computer simulation showed that the first supermassive black holes can arise in rare turbulent clumps of gas, called primordial halos, that were fed by unusually strong streams of cold gas. The key simulation result was that cold flows suppressed star formation in the turbulent halo until the halo's gravity was finally able to overcome the turbulence and formed two direct-collapse black holes of {{Solar mass|31,000}} and {{Solar mass|40,000}}. The birth of the first SMBHs can therefore be a result of standard cosmological structure formation.{{cite journal |title=Revealing the origin of the first supermassive black holes |journal=Nature |date=6 July 2022 |doi=10.1038/d41586-022-01560-y |pmid=35794378 |quote=State-of-the-art computer simulations show that the first supermassive black holes were born in rare, turbulent reservoirs of gas in the primordial Universe without the need for finely tuned, exotic environments — contrary to what has been thought for almost two decades.|doi-access=free }}{{cite web |title=Scientists discover how first quasars in universe formed |url=https://phys.org/news/2022-07-scientists-quasars-universe.html |website=phys.org |publisher=Provided by University of Portsmouth |access-date=2 August 2022 |date=6 July 2022}}

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| image1 = Artist’s impression of the huge outflow ejected from the quasar SDSS J1106+1939.jpg

| image2 = Artist’s illustration of galaxy with jets from a supermassive black hole.jpg

| caption1 = Artist's impression of the huge outflow ejected from the quasar SDSS J1106+1939{{cite news|title=Biggest Black Hole Blast Discovered|url=http://www.eso.org/public/news/eso1247/|access-date=November 28, 2012|newspaper=ESO Press Release}}

| caption2 = Artist's illustration of galaxy with jets from a supermassive black hole{{cite web | title=Artist's illustration of galaxy with jets from a supermassive black hole | url=https://www.spacetelescope.org/images/heic1511a/ | website=Hubble Space Telescope | access-date=November 27, 2018}}

}}

Primordial black holes (PBHs) could have been produced directly from external pressure in the first moments after the Big Bang. These black holes would then have more time than any of the above models to accrete, allowing them sufficient time to reach supermassive sizes. Formation of black holes from the deaths of the first stars has been extensively studied and corroborated by observations. The other models for black hole formation listed above are theoretical.

The formation of a supermassive black hole requires a relatively small volume of highly dense matter having small angular momentum. Normally, the process of accretion involves transporting a large initial endowment of angular momentum outwards, and this appears to be the limiting factor in black hole growth. This is a major component of the theory of accretion disks. Gas accretion is both the most efficient and the most conspicuous way in which black holes grow. The majority of the mass growth of supermassive black holes is thought to occur through episodes of rapid gas accretion, which are observable as active galactic nuclei or quasars.

Observations reveal that quasars were much more frequent when the Universe was younger, indicating that supermassive black holes formed and grew early. A major constraining factor for theories of supermassive black hole formation is the observation of distant luminous quasars, which indicate that supermassive black holes of {{solar mass|billions of}} had already formed when the Universe was less than one billion years old. This suggests that supermassive black holes arose very early in the Universe, inside the first massive galaxies.{{citation needed|date=November 2022}}

File:Artist’s impression of stars born in winds from supermassive black holes.jpg

There is a natural upper limit to how large supermassive black holes can grow. Supermassive black holes in any quasar or active galactic nucleus (AGN) appear to have a theoretical upper limit of physically around {{solar mass|50 billion}} for typical parameters, as anything above this slows growth down to a crawl (the slowdown tends to start around {{solar mass|10 billion}}) and causes the unstable accretion disk surrounding the black hole to coalesce into stars that orbit it.{{cite web | url=https://futurism.com/is-there-a-size-limit-to-how-large-a-black-hole-can-become | title=Is There a Limit to How Large Black Holes Can Become? | first1=Jaime | last1=Trosper | date=May 5, 2014 | website=futurism.com | access-date=November 27, 2018}}{{cite web | url=https://www.science.org/content/article/limit-how-big-black-holes-can-grow-astonishing | title=Limit to how big black holes can grow is astonishing | first1=Daniel | last1=Clery | date=December 21, 2015 | website=sciencemag.org | access-date=November 27, 2018}}{{cite web | url=https://www2.le.ac.uk/offices/press/press-releases/2015/december/black-holes-could-grow-as-large-as-50-billion-suns-before-their-food-crumbles-into-stars-research-shows | title=Black holes could grow as large as 50 billion suns before their food crumbles into stars, research shows | publisher=University of Leicester | access-date=November 27, 2018 | archive-date=October 25, 2021 | archive-url=https://web.archive.org/web/20211025005826/https://www2.le.ac.uk/offices/press/press-releases/2015/december/black-holes-could-grow-as-large-as-50-billion-suns-before-their-food-crumbles-into-stars-research-shows | url-status=dead }} A study concluded that the radius of the innermost stable circular orbit (ISCO) for SMBH masses above this limit exceeds the self-gravity radius, making disc formation no longer possible.

A larger upper limit of around {{solar mass|270 billion}} was represented as the absolute maximum mass limit for an accreting SMBH in extreme cases, for example its maximal prograde spin with a dimensionless spin parameter of a = 1, although the maximum limit for a black hole's spin parameter is very slightly lower at a = 0.9982.{{cite journal|arxiv=1007.4279|doi=10.1111/j.1365-2966.2011.19099.x |title=Maximal spin and energy conversion efficiency in a symbiotic system of black hole, disc and jet |year=2011 |last1=Kovács |first1=Zoltán |last2=Gergely |first2=Lászlóá. |last3=Biermann |first3=Peter L. |journal=Monthly Notices of the Royal Astronomical Society |volume=416 |issue=2 |pages=991–1009 |doi-access=free |bibcode=2011MNRAS.416..991K |s2cid=119255235 }} At masses just below the limit, the disc luminosity of a field galaxy is likely to be below the Eddington limit and not strong enough to trigger the feedback underlying the M–sigma relation, so SMBHs close to the limit can evolve above this.

It was noted that, black holes close to this limit are likely to be rather even rarer, as it would require the accretion disc to be almost permanently prograde because the black hole grows and the spin-down effect of retrograde accretion is larger than the spin-up by prograde accretion, due to its ISCO and therefore its lever arm. This would require the hole spin to be permanently correlated with a fixed direction of the potential controlling gas flow, within the black hole's host galaxy, and thus would tend to produce a spin axis and hence AGN jet direction, which is similarly aligned with the galaxy. Current observations do not support this correlation.

The so-called 'chaotic accretion' presumably has to involve multiple small-scale events, essentially random in time and orientation if it is not controlled by a large-scale potential in this way. This would lead the accretion statistically to spin-down, due to retrograde events having larger lever arms than prograde, and occurring almost as often. There is also other interactions with large SMBHs that trend to reduce their spin, including particularly mergers with other black holes, which can statistically decrease the spin. All of these considerations suggested that SMBHs usually cross the critical theoretical mass limit at modest values of their spin parameters, so that {{val|5|e=10|u={{solar mass}}}} in all but rare cases.

Although modern UMBHs within quasars and galactic nuclei cannot grow beyond around {{val|5|-|27|e=10|u={{solar mass}}}} through the accretion disk and as well given the current age of the universe, some of these monster black holes in the universe are predicted to still continue to grow up to stupendously large masses of perhaps {{val|e=14|u={{solar mass}}}} during the collapse of superclusters of galaxies in the extremely far future of the universe.

{{main|Active galactic nucleus|Galaxy formation and evolution}}

Gravitation from supermassive black holes in the center of many galaxies is thought to power active objects such as Seyfert galaxies and quasars, and the relationship between the mass of the central black hole and the mass of the host galaxy depends upon the galaxy type.{{cite journal| title=Supermassive Black Holes and Their Host Spheroids. II. The Red and Blue Sequence in the M_BH-M_*,sph Diagram |journal=Astrophysical Journal|date=2016 | volume=817 | page=21 |last1=Savorgnan |first1=Giulia A.D. | last2=Graham| first2=Alister W. | last3=Marconi| first3=Alessandro | last4=Sani| first4=Eleonora |issue=1|doi=10.3847/0004-637X/817/1/21|arxiv=1511.07437| bibcode=2016ApJ...817...21S|s2cid=55698824 |doi-access=free }}{{cite journal| title=Black Hole Mass Scaling Relations for Early-type Galaxies. I. M_BH-M_*,sph and M_BH-M_*,gal |journal=Astrophysical Journal|date=2019 | volume=876 | page=155 |last1=Sahu |first1=Nandini | last2=Graham| first2=Alister W. | last3=Davis| first3=Benjamin L. |issue=2|doi=10.3847/1538-4357/ab0f32|arxiv=1903.04738| bibcode=2019ApJ...876..155S|s2cid=209877088 |doi-access=free }} An empirical correlation between the size of supermassive black holes and the stellar velocity dispersion $\backslash sigma$ of a galaxy bulge{{cite journal |author=Gultekin K |display-authors=etal |date=2009 |bibcode=2009ApJ...698..198G |title=The M—σ and M-L Relations in Galactic Bulges, and Determinations of Their Intrinsic Scatter |journal=The Astrophysical Journal |volume=698 |issue=1 |pages=198–221 |doi=10.1088/0004-637X/698/1/198|arxiv = 0903.4897 |s2cid=18610229 }} is called the M–sigma relation.

An AGN is now considered to be a galactic core hosting a massive black hole that is accreting matter and displays a sufficiently strong luminosity. The nuclear region of the Milky Way, for example, lacks sufficient luminosity to satisfy this condition. The unified model of AGN is the concept that the large range of observed properties of the AGN taxonomy can be explained using just a small number of physical parameters. For the initial model, these values consisted of the angle of the accretion disk's torus to the line of sight and the luminosity of the source. AGN can be divided into two main groups: a radiative mode AGN in which most of the output is in the form of electromagnetic radiation through an optically thick accretion disk, and a jet mode in which relativistic jets emerge perpendicular to the disk.{{cite journal | title=Revisiting the Unified Model of Active Galactic Nuclei | last1=Netzer | first1=Hagai | journal=Annual Review of Astronomy and Astrophysics | volume=53 | pages=365–408 | date=August 2015 | doi=10.1146/annurev-astro-082214-122302 | bibcode=2015ARA&A..53..365N | arxiv=1505.00811 | s2cid=119181735 }}

{{main|Binary black hole}}

The interaction of a pair of SMBH-hosting galaxies can lead to merger events. Dynamical friction on the hosted SMBH objects causes them to sink toward the center of the merged mass, eventually forming a pair with a separation of under a kiloparsec. The interaction of this pair with surrounding stars and gas will then gradually bring the SMBH together as a gravitationally bound binary system with a separation of ten parsecs or less. Once the pair draw as close as 0.001 parsecs, gravitational radiation will cause them to merge. By the time this happens, the resulting galaxy will have long since relaxed from the merger event, with the initial starburst activity and AGN having faded away.{{cite journal | title=Dancing to CHANGA: a self-consistent prediction for close SMBH pair formation time-scales following galaxy mergers | display-authors=1 | last1=Tremmel | first1=M. | last2=Governato | first2=F. | last3=Volonteri | first3=M. | last4=Quinn | first4=T. R. | last5=Pontzen | first5=A. | journal=Monthly Notices of the Royal Astronomical Society | volume=475 | issue=4 | pages=4967–4977 | date=April 2018 | doi=10.1093/mnras/sty139 | doi-access=free | arxiv=1708.07126 | bibcode=2018MNRAS.475.4967T }}

File:Runaway Black Holes.jpg

The gravitational waves from this coalescence can give the resulting SMBH a velocity boost of up to several thousand km/s, propelling it away from the galactic center and possibly even ejecting it from the galaxy. This phenomenon is called a gravitational recoil.{{cite journal | title=Recoiling Black Holes: Electromagnetic Signatures, Candidates, and Astrophysical Implications | last=Komossa | first=S. | journal=Advances in Astronomy | volume=2012 | id=364973 | date=2012 | page=364973 | doi=10.1155/2012/364973 | arxiv=1202.1977 | bibcode=2012AdAst2012E..14K | doi-access=free }} The other possible way to eject a black hole is the classical slingshot scenario, also called slingshot recoil. In this scenario first a long-lived binary black hole forms through a merger of two galaxies. A third SMBH is introduced in a second merger and sinks into the center of the galaxy. Due to the three-body interaction one of the SMBHs, usually the lightest, is ejected. Due to conservation of linear momentum the other two SMBHs are propelled in the opposite direction as a binary. All SMBHs can be ejected in this scenario.{{Cite journal |last1=Saslaw |first1=William C. |last2=Valtonen |first2=Mauri J. |last3=Aarseth |first3=Sverre J. |date=1974-06-01 |title=The Gravitational Slingshot and the Structure of Extragalactic Radio Sources |journal=The Astrophysical Journal |volume=190 |pages=253–270 |doi=10.1086/152870 |bibcode=1974ApJ...190..253S |issn=0004-637X|doi-access=free }} An ejected black hole is called a runaway black hole.

There are different ways to detect recoiling black holes. Often a displacement of a quasar/AGN from the center of a galaxy{{Cite journal |last1=Magain |first1=Pierre |last2=Letawe |first2=Géraldine |last3=Courbin |first3=Frédéric |last4=Jablonka |first4=Pascale |last5=Jahnke |first5=Knud |last6=Meylan |first6=Georges |last7=Wisotzki |first7=Lutz |date=2005-09-01 |title=Discovery of a bright quasar without a massive host galaxy |url=https://ui.adsabs.harvard.edu/abs/2005Natur.437..381M |journal=Nature |volume=437 |issue=7057 |pages=381–384 |doi=10.1038/nature04013 |pmid=16163349 |arxiv=astro-ph/0509433 |bibcode=2005Natur.437..381M |s2cid=4303895 |issn=0028-0836}} or a spectroscopic binary nature of a quasar/AGN is seen as evidence for a recoiled black hole.{{Cite journal |last1=Komossa |first1=S. |last2=Zhou |first2=H. |last3=Lu |first3=H. |date=2008-05-01 |title=A Recoiling Supermassive Black Hole in the Quasar SDSS J092712.65+294344.0? |url=https://ui.adsabs.harvard.edu/abs/2008ApJ...678L..81K |journal=The Astrophysical Journal |volume=678 |issue=2 |pages=L81 |doi=10.1086/588656 |arxiv=0804.4585 |bibcode=2008ApJ...678L..81K |s2cid=6860884 |issn=0004-637X}}

Candidate recoiling black holes include NGC 3718,{{Cite journal |last1=Markakis |first1=K. |last2=Dierkes |first2=J. |last3=Eckart |first3=A. |last4=Nishiyama |first4=S. |last5=Britzen |first5=S. |last6=García-Marín |first6=M. |last7=Horrobin |first7=M. |last8=Muxlow |first8=T. |last9=Zensus |first9=J. A. |date=2015-08-01 |title=Subaru and e-Merlin observations of NGC 3718. Diaries of a supermassive black hole recoil? |url=https://ui.adsabs.harvard.edu/abs/2015A&A...580A..11M |journal=Astronomy and Astrophysics |volume=580 |pages=A11 |doi=10.1051/0004-6361/201425077 |arxiv=1504.03691 |bibcode=2015A&A...580A..11M |s2cid=56022608 |issn=0004-6361}} SDSS1133,{{Cite journal |last1=Koss |first1=Michael |last2=Blecha |first2=Laura |last3=Mushotzky |first3=Richard |last4=Hung |first4=Chao Ling |last5=Veilleux |first5=Sylvain |last6=Trakhtenbrot |first6=Benny |last7=Schawinski |first7=Kevin |last8=Stern |first8=Daniel |last9=Smith |first9=Nathan |last10=Li |first10=Yanxia |last11=Man |first11=Allison |last12=Filippenko |first12=Alexei V. |last13=Mauerhan |first13=Jon C. |last14=Stanek |first14=Kris |last15=Sanders |first15=David |date=2014-11-01 |title=SDSS1133: an unusually persistent transient in a nearby dwarf galaxy |journal=Monthly Notices of the Royal Astronomical Society |volume=445 |issue=1 |pages=515–527 |doi=10.1093/mnras/stu1673 |doi-access=free |arxiv=1401.6798 |bibcode=2014MNRAS.445..515K |issn=0035-8711}} 3C 186,{{Cite journal |last1=Chiaberge |first1=M. |last2=Ely |first2=J. C. |last3=Meyer |first3=E. T. |last4=Georganopoulos |first4=M. |last5=Marinucci |first5=A. |last6=Bianchi |first6=S. |last7=Tremblay |first7=G. R. |last8=Hilbert |first8=B. |last9=Kotyla |first9=J. P. |last10=Capetti |first10=A. |last11=Baum |first11=S. A. |last12=Macchetto |first12=F. D. |last13=Miley |first13=G. |last14=O'Dea |first14=C. P. |last15=Perlman |first15=E. S. |date=2017-04-01 |title=The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source? |url=https://ui.adsabs.harvard.edu/abs/2017A&A...600A..57C |journal=Astronomy and Astrophysics |volume=600 |pages=A57 |doi=10.1051/0004-6361/201629522 |arxiv=1611.05501 |bibcode=2017A&A...600A..57C |s2cid=27351189 |issn=0004-6361}} E1821+643{{Cite journal |last1=Jadhav |first1=Yashashree |last2=Robinson |first2=Andrew |last3=Almeyda |first3=Triana |last4=Curran |first4=Rachel |last5=Marconi |first5=Alessandro |date=2021-10-01 |title=The spatially offset quasar E1821+643: new evidence for gravitational recoil |journal=Monthly Notices of the Royal Astronomical Society |volume=507 |issue=1 |pages=484–495 |doi=10.1093/mnras/stab2176 |doi-access=free |arxiv=2107.14711 |bibcode=2021MNRAS.507..484J |issn=0035-8711}} and SDSSJ0927+2943. Candidate runaway black holes are HE0450–2958, CID-42{{Cite journal |last1=Civano |first1=F. |last2=Elvis |first2=M. |last3=Lanzuisi |first3=G. |last4=Jahnke |first4=K. |last5=Zamorani |first5=G. |last6=Blecha |first6=L. |last7=Bongiorno |first7=A. |last8=Brusa |first8=M. |last9=Comastri |first9=A. |last10=Hao |first10=H. |last11=Leauthaud |first11=A. |last12=Loeb |first12=A. |last13=Mainieri |first13=V. |last14=Piconcelli |first14=E. |last15=Salvato |first15=M. |date=2010-07-01 |title=A Runaway Black Hole in COSMOS: Gravitational Wave or Slingshot Recoil? |url=https://ui.adsabs.harvard.edu/abs/2010ApJ...717..209C |journal=The Astrophysical Journal |volume=717 |issue=1 |pages=209–222 |doi=10.1088/0004-637X/717/1/209 |arxiv=1003.0020 |bibcode=2010ApJ...717..209C |s2cid=20466072 |issn=0004-637X}} and objects around RCP 28.{{cite journal |last1=van Dokkum |first1=Pieter |last2=Pasha |first2=Imad |last3=Buzzo |first3=Maria Luisa |last4=LaMassa |first4=Stephanie |last5=Shen |first5=Zili |last6=Keim |first6=Michael A. |last7=Abraham |first7=Roberto |last8=Conroy |first8=Charlie |last9=Danieli |first9=Shany |last10=Mitra |first10=Kaustav |last11=Nagai |first11=Daisuke |last12=Natarajan |first12=Priyamvada |last13=Romanowsky |first13=Aaron J. |last14=Tremblay |first14=Grant |last15=Urry |first15=C. Megan |date=March 2023 |title=A candidate runaway supermassive black hole identified by shocks and star formation in its wake |journal=The Astrophysical Journal Letters |volume= 946|issue= 2|pages= L50|arxiv=2302.04888 |bibcode=2023ApJ...946L..50V |doi= 10.3847/2041-8213/acba86|last16=van den Bosch |first16=Frank C.|s2cid=256808376 |doi-access=free }} Runaway supermassive black holes may trigger star formation in their wakes.{{cite journal |last1=de la Fuente Marcos |first1=R. |last2=de la Fuente Marcos |first2=C. |date=April 2008 |title=The Invisible Hand: Star Formation Triggered by Runaway Black Holes |journal=The Astrophysical Journal Letters |volume=677 |issue=1 |pages=L47 |arxiv= |bibcode=2008ApJ...677L..47D |doi=10.1086/587962|s2cid=250885688 |doi-access=free }} A linear feature near the dwarf galaxy RCP 28 was interpreted as the star-forming wake of a candidate runaway black hole.{{cite web |last=Japelj |first=Jure |date=February 22, 2023 |title=Have Scientists Found a Rogue Supermassive Black Hole? |url=https://skyandtelescope.org/astronomy-news/have-scientists-found-rogue-supermassive-black-hole/}}{{cite web |last=Grossman |first=Lisa |date=March 10, 2023 |title=A runaway black hole has been spotted fleeing a distant galaxy |url=https://www.sciencenews.org/article/runaway-black-hole-galaxy-hubble}} Later it was however found that this feature is likely a bulge-less edge-on galaxy.{{Cite journal |last1=Sánchez Almeida |first1=Jorge |last2=Montes |first2=Mireia |last3=Trujillo |first3=Ignacio |date=2023-05-01 |title=Supermassive black hole wake or bulgeless edge-on galaxy? |url=https://ui.adsabs.harvard.edu/abs/2023A&A...673L...9S/abstract |journal=Astronomy and Astrophysics |volume=673 |pages=L9 |arxiv=2304.12344 |bibcode=2023A&A...673L...9S |doi=10.1051/0004-6361/202346430 |issn=0004-6361}}{{Cite journal |last1=Montes |first1=Mireia |last2=Sánchez Almeida |first2=Jorge |last3=Trujillo |first3=Ignacio |date=2024-06-01 |title=Deep HST Imaging Favors the Bulgeless Edge-on Galaxy Explanation for the Hypothetical Stellar Wake Created by a Runaway Supermassive Black Hole |journal=Research Notes of the American Astronomical Society |volume=8 |issue=6 |pages=150 |arxiv=2406.00102 |bibcode=2024RNAAS...8..150M |doi=10.3847/2515-5172/ad530b |doi-access=free |issn=2515-5172}}

{{main|Hawking radiation}}

Hawking radiation is black-body radiation that is predicted to be released by black holes, due to quantum effects near the event horizon. This radiation reduces the mass and energy of black holes, causing them to shrink and ultimately vanish. If black holes evaporate via Hawking radiation, a non-rotating and uncharged stupendously large black hole with a mass of {{val|1|e=11|u={{solar mass}}}} will evaporate in around {{val|2.1|e=100|ul=years}}.{{cite journal | doi = 10.1103/PhysRevD.13.198 | volume=13 | title=Particle emission rates from a black hole: Massless particles from an uncharged, nonrotating hole | year=1976 | journal=Physical Review D | pages=198–206 | last1 = Page | first1 = Don N. | issue=2 | bibcode=1976PhRvD..13..198P}}. See in particular equation (27). Black holes formed during the predicted collapse of superclusters of galaxies in the far future with {{val|1|e=14|u={{solar mass}}}} would evaporate over a timescale of up to {{val|2.1|e=109|u=years}}.{{cite journal | last1 = Frautschi | first1 = S | year = 1982 | title = Entropy in an expanding universe | journal = Science | volume = 217 | issue = 4560| pages = 593–599 | doi = 10.1126/science.217.4560.593 | pmid = 17817517 | bibcode = 1982Sci...217..593F | s2cid = 27717447 |quote= p. 596: table 1 and section "black hole decay" and previous sentence on that page: "Since we have assumed a maximum scale of gravitational binding – for instance, superclusters of galaxies – black hole formation eventually comes to an end in our model, with masses of up to {{val|e=14|u={{solar mass}}}} ... the timescale for black holes to radiate away all their energy ranges ... to {{val|e=106|u=years}} for black holes of up to {{val|e=14|u={{solar mass}}}}}}

File:ionringBlackhole.jpeg. This image shows the result of bending of light from behind the black hole, and it also shows the asymmetry arising by the Doppler effect from the extremely high orbital speed of the matter in the ring.]]

Some of the best evidence for the presence of black holes is provided by the Doppler effect whereby light from nearby orbiting matter is red-shifted when receding and blue-shifted when advancing. For matter very close to a black hole the orbital speed must be comparable with the speed of light, so receding matter will appear very faint compared with advancing matter, which means that systems with intrinsically symmetric discs and rings will acquire a highly asymmetric visual appearance. This effect has been allowed for in modern computer-generated images such as the example presented here, based on a plausible model{{cite journal | last1 = Straub | first1 = O. | last2 = Vincent | first2 = F. H. | last3 = Abramowicz | first3 = M. A. | last4 = Gourgoulhon | first4 = E. | last5 = Paumard | first5 = T. | year = 2012 | title = Modelling the black hole silhouette in Sgr A* with ion tori | journal = Astronomy & Astrophysics | volume = 543 | page = A83 | doi = 10.1051/0004-6361/201219209 | doi-access = free | arxiv = 1203.2618 }} for the supermassive black hole in Sgr A* at the center of the Milky Way. However, the resolution provided by presently available telescope technology is still insufficient to confirm such predictions directly.

What already has been observed directly in many systems are the lower non-relativistic velocities of matter orbiting further out from what are presumed to be black holes. Direct Doppler measures of water masers surrounding the nuclei of nearby galaxies have revealed a very fast Keplerian motion, only possible with a high concentration of matter in the center. Currently, the only known objects that can pack enough matter in such a small space are black holes, or things that will evolve into black holes within astrophysically short timescales. For active galaxies farther away, the width of broad spectral lines can be used to probe the gas orbiting near the event horizon. The technique of reverberation mapping uses variability of these lines to measure the mass and perhaps the spin of the black hole that powers active galaxies.

File:Galactic centre orbits.svg{{cite journal | last1 = Eisenhauer|first1=F. | display-authors = etal | date = 2005 | title = SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month | journal = The Astrophysical Journal | volume = 628 | issue = 1 | pages = 246–259 | doi=10.1086/430667|arxiv = astro-ph/0502129 |bibcode = 2005ApJ...628..246E |s2cid=122485461 }}]]

Evidence indicates that the Milky Way galaxy has a supermassive black hole at its center, 26,000 light-years from the Solar System, in a region called Sagittarius A*{{cite news|url=https://www.thetimes.com/uk/science/article/astronomers-confirm-black-hole-at-the-heart-of-the-milky-way-m0vtxv52v26|title=Astronomers confirm black hole at the heart of the Milky Way|last=Henderson|first=Mark|date=December 9, 2008 |work=The Times |access-date=May 17, 2009|location=London}} because:

• The star S2 follows an elliptical orbit with a period of 15.2 years and a pericenter (closest distance) of 17 light-hours ({{val|1.8|e=13|u=m}} or 120 AU) from the center of the central object.
• From the motion of star S2, the object's mass can be estimated as {{solar mass|4.0 million}},{{cite journal | doi=10.3847/2041-8213/ac6674 | title=First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way | year=2022 | last1=Event Horizon Telescope Collaboration | last2=Akiyama | first2=Kazunori | last3=Alberdi | first3=Antxon | last4=Alef | first4=Walter | last5=Algaba | first5=Juan Carlos | last6=Anantua | first6=Richard | last7=Asada | first7=Keiichi | last8=Azulay | first8=Rebecca | last9=Bach | first9=Uwe | last10=Baczko | first10=Anne-Kathrin | last11=Ball | first11=David | last12=Baloković | first12=Mislav | last13=Barrett | first13=John | last14=Bauböck | first14=Michi | last15=Benson | first15=Bradford A. | last16=Bintley | first16=Dan | last17=Blackburn | first17=Lindy | last18=Blundell | first18=Raymond | last19=Bouman | first19=Katherine L. | last20=Bower | first20=Geoffrey C. | last21=Boyce | first21=Hope | last22=Bremer | first22=Michael | last23=Brinkerink | first23=Christiaan D. | last24=Brissenden | first24=Roger | last25=Britzen | first25=Silke | last26=Broderick | first26=Avery E. | last27=Broguiere | first27=Dominique | last28=Bronzwaer | first28=Thomas | last29=Bustamante | first29=Sandra | last30=Byun | first30=Do-Young | journal=The Astrophysical Journal Letters | volume=930 | issue=2 | pages=L12 | bibcode=2022ApJ...930L..12E | s2cid=248744791 | display-authors=1 | doi-access=free | hdl=10261/278882 | hdl-access=free }} or about {{val|7.96|e=36|u=kg}}.
• The radius of the central object must be less than 17 light-hours, because otherwise S2 would collide with it. Observations of the star S14{{cite journal |last1=Ghez |first1=A. M. |author1-link=Andrea Ghez |last2=Salim |first2=S. |last3=Hornstein |first3=S. D. |last4=Tanner |first4=A. |last5=Lu |first5=J. R. |last6=Morris |first6=M. |last7=Becklin |first7=E. E. |last8= Duchêne |first8=G. |title=Stellar Orbits around the Galactic Center Black Hole |journal=The Astrophysical Journal |volume=620 |issue=2 |pages=744–757 |date=May 2005 |arxiv=astro-ph/0306130 |doi=10.1086/427175|bibcode = 2005ApJ...620..744G |s2cid=8656531 }} indicate that the radius is no more than 6.25 light-hours, about the diameter of Uranus' orbit.
• No known astronomical object other than a black hole can contain {{solar mass|4.0 million}} in this volume of space.

Infrared observations of bright flare activity near Sagittarius A* show orbital motion of plasma with a period of {{Val|45|15|u=minutes}} at a separation of six to ten times the gravitational radius of the candidate SMBH. This emission is consistent with a circularized orbit of a polarized "hot spot" on an accretion disk in a strong magnetic field. The radiating matter is orbiting at 30% of the speed of light just outside the innermost stable circular orbit.{{cite journal | title=Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA* | last1=Gravity Collaboration | last2=Abuter | first2=R. | last3=Amorim | first3=A. | last4=Bauböck | first4=M. | last5=Berger | first5=J. P. | last6=Bonnet | first6=H. | last7=Brandner | first7=W. | last8=Clénet | first8=Y. | last9=Coudé Du Foresto | first9=V. | last10=de Zeeuw | first10=P. T. | last11=Deen | first11=C. | last12=Dexter | first12=J. | last13=Duvert | first13=G. | last14=Eckart | first14=A. | last15=Eisenhauer | first15=F. | last16=Förster Schreiber | first16=N. M. | last17=Garcia | first17=P. | last18=Gao | first18=F. | last19=Gendron | first19=E. | last20=Genzel | first20=R. | last21=Gillessen | first21=S. | last22=Guajardo | first22=P. | last23=Habibi | first23=M. | last24=Haubois | first24=X. | last25=Henning | first25=Th. | last26=Hippler | first26=S. | last27=Horrobin | first27=M. | last28=Huber | first28=A. | last29=Jiménez-Rosales | first29=A. | last30=Jocou | first30=L. | last31=Kervella | first31=P. | last32=Lacour | first32=S. | last33=Lapeyrère | first33=V. | last34=Lazareff | first34=B. | last35=Le Bouquin | first35=J.-B. | last36=Léna | first36=P. | last37=Lippa | first37=M. | last38=Ott | first38=T. | last39=Panduro | first39=J. | last40=Paumard | first40=T. | last41=Perraut | first41=K. | last42=Perrin | first42=G. | last43=Pfuhl | first43=O. | last44=Plewa | first44=P. M. | last45=Rabien | first45=S. | last46=Rodríguez-Coira | first46=G. | last47=Rousset | first47=G. | last48=Sternberg | first48=A. | last49=Straub | first49=O. | last50=Straubmeier | first50=C. | last51=Sturm | first51=E. | last52=Tacconi | first52=L. J. | last53=Vincent | first53=F. | last54=von Fellenberg | first54=S. | last55=Waisberg | first55=I. | last56=Widmann | first56=F. | last57=Wieprecht | first57=E. | last58=Wiezorrek | first58=E. | last59=Woillez | first59=J. | last60=Yazici | first60=S. | display-authors=1 | journal=Astronomy & Astrophysics | volume=618 | id=L10 | pages=15 | date=October 2018 | doi=10.1051/0004-6361/201834294 | bibcode=2018A&A...618L..10G | arxiv=1810.12641 | s2cid=53613305 }}

On January 5, 2015, NASA reported observing an X-ray flare 400 times brighter than usual, a record-breaker, from Sagittarius A*. The unusual event may have been caused by the breaking apart of an asteroid falling into the black hole or by the entanglement of magnetic field lines within gas flowing into Sagittarius A*, according to astronomers.{{cite web |last1=Chou |first1=Felicia |last2=Anderson |first2=Janet |last3=Watzke |first3=Megan |title=Release 15-001 – NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole |url=http://www.nasa.gov/press/2015/january/nasa-s-chandra-detects-record-breaking-outburst-from-milky-way-s-black-hole/ |date=January 5, 2015 |publisher=NASA |access-date=January 6, 2015 }}

{{multiple image

| align = center

| image1 = X-RayFlare-BlackHole-MilkyWay-20140105.jpg

| width1 = 400

| caption1 = Detection of an unusually bright X-ray flare from Sagittarius A*, a supermassive black hole in the center of the Milky Way galaxy

| image2 = EHT Saggitarius A black hole.tif

| width2 = 400

| caption2 = Sagittarius A* imaged by the Event Horizon Telescope

| caption_align = center

}}

File:rxj1242 comp.jpg – X-ray (left) and optical (right).{{cite web|url=http://chandra.harvard.edu/photo/2004/rxj1242/|title=Chandra :: Photo Album :: RX J1242-11 :: 18 Feb 04|website=chandra.harvard.edu}}]]

Unambiguous dynamical evidence for supermassive black holes exists only for a handful of galaxies;{{cite book |last=Merritt|first=David|author-link=David Merritt|title=Dynamics and Evolution of Galactic Nuclei |url=http://press.princeton.edu/titles/10040.html |date=2013 |publisher=Princeton University Press |location=Princeton, New Jersey |isbn=9780691158600 |page=23}} these include the Milky Way, the Local Group galaxies M31 and M32, and a few galaxies beyond the Local Group, such as NGC 4395. In these galaxies, the root mean square (or rms) velocities of the stars or gas rises proportionally to 1/{{var|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.{{cite journal

|last=King|first=Andrew|date=September 15, 2003|title=Black Holes, Galaxy Formation, and the MBH-σ Relation|journal=The Astrophysical Journal Letters |volume=596 |issue=1|pages=L27–L29|arxiv = astro-ph/0308342 |bibcode = 2003ApJ...596L..27K |doi = 10.1086/379143 |s2cid=9507887}} The reason for this assumption is the M–sigma relation, a tight (low scatter) relation between the mass of the hole in the 10 or so galaxies with secure detections, and the velocity dispersion of the stars in the bulges of those galaxies.{{cite journal |bibcode=2000ApJ...539L...9F |last1=Ferrarese| first1=Laura|last2=Merritt| first2=David|author-link2=David Merritt|date=August 10, 2000|title=A Fundamental Relation between Supermassive Black Holes and Their Host Galaxies|journal=The Astrophysical Journal|pages=L9–12|doi=10.1086/312838|issue=1|volume=539|arxiv = astro-ph/0006053 |s2cid=6508110}} 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.

On March 28, 2011, a supermassive black hole was seen tearing a mid-size star apart.{{cite news|url=https://www.smh.com.au/technology/sci-tech/astronomers-catch-first-glimpse-of-star-being-consumed-by-black-hole-20110826-1jd23.html?from=smh_sb|title=Astronomers catch first glimpse of star being consumed by black hole | work=The Sydney Morning Herald | date=August 26, 2011}} That is the only likely explanation of the observations that day of sudden X-ray radiation and the follow-up broad-band observations.{{cite journal | last1=Burrows |first1=D. N. | last2=Kennea |first2=J. A. | last3=Ghisellini |first3=G. | last4=Mangano |first4=V. | display-authors=etal | title=Relativistic jet activity from the tidal disruption of a star by a massive black hole | journal=Nature | volume=476 | issue=7361 | pages=421–424 |date=August 2011 |doi = 10.1038/nature10374 | arxiv=1104.4787 |bibcode = 2011Natur.476..421B | pmid=21866154| s2cid=4369797 }}{{cite journal | last1=Zauderer |first1=B. A. | last2=Berger |first2=E. | last3=Soderberg |first3=A. M. |author3-link= Alicia M. Soderberg | last4=Loeb |first4=A. | display-authors=etal | title=Birth of a relativistic outflow in the unusual γ-ray transient Swift J164449.3+573451 | journal=Nature | volume=476 | issue=7361 | pages=425–428 |date=August 2011 |doi = 10.1038/nature10366 | arxiv=1106.3568 |bibcode = 2011Natur.476..425Z | pmid=21866155| s2cid=205226085 }} 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 {{solar mass|million}}. 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.

File:M87 jet.jpg photograph of the 4,400 light-year-long relativistic jet of Messier 87, which is matter being ejected by the {{solar mass|{{val|6.5e9}}}} supermassive black hole at the center of the galaxy]]

The nearby Andromeda Galaxy, 2.5 million light-years away, contains a {{solar mass|{{val|1.4|0.65|0.45|e=8}} (140 million)}} central black hole, significantly larger than the Milky Way's.{{cite book | doi=10.1063/5.0027838| chapter=Determine the mass of supermassive black hole in the centre of M31 in different methods| title=International Conference of Numerical Analysis and Applied Mathematics Icnaam 2019| year=2020| last1=Al-Baidhany| first1=Ismaeel A.| last2=Chiad| first2=Sami S.| last3=Jabbar| first3=Wasmaa A.| last4=Al-Kadumi| first4=Ahmed K.| last5=Habubi| first5=Nadir F.| last6=Mansour| first6=Hazim L.| journal=American Institute of Physics Conference Series| volume=2293| issue=1| page=050050| bibcode=2020AIPC.2290e0050A| s2cid=230970967}} The largest supermassive black hole in the Milky Way's vicinity appears to be that of Messier 87 (i.e., M87*), at a mass of {{nowrap|{{solar mass|{{val|6.5|0.7|e=9}} (c. 6.5 billion)}}}} at a distance of 48.92 million light-years.{{cite journal |last1=The Event Horizon Telescope Collaboration |title=First M87 Event Horizon Telescope results. VI. The shadow and mass of the central black hole |journal=The Astrophysical Journal |date=10 April 2019 |volume=875 |issue=1 |pages=L6 |doi=10.3847/2041-8213/ab1141 |arxiv=1906.11243 |bibcode=2019ApJ...875L...6E |s2cid=145969867 |url=https://repository.ubn.ru.nl/bitstream/2066/202545/1/202545.pdf |doi-access=free }} 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 {{solar mass|{{val|2.1|3.5|1.3|e=10}} (21 billion)}}.{{cite journal|last=Dullo|first=B.T.|title=The Most Massive Galaxies with Large Depleted Cores: Structural Parameter Relations and Black Hole Masses|journal=The Astrophysical Journal|date=22 November 2019|volume=886|issue=2|page=80|arxiv=1910.10240|bibcode=2019ApJ...886...80D|doi=10.3847/1538-4357/ab4d4f|s2cid=204838306 |doi-access=free }}

Masses of black holes in quasars can be estimated via indirect methods that are subject to substantial uncertainty. The quasar TON 618 is an example of an object with an extremely large black hole, estimated at {{solar mass|{{val|4.07e10}} (40.7 billion)}}.{{cite journal|last1=Shemmer|first1=O.|last2=Netzer|first2=H.|last3=Maiolino|first3=R.|last4=Oliva|first4=E.|last5=Croom|first5=S.|last6=Corbett|first6=E.|last7=di Fabrizio|first7=L.|title=Near-infrared spectroscopy of high-redshift active galactic nuclei: I. A metallicity-accretion rate relationship|journal=The Astrophysical Journal|date=2004|volume=614|issue=2|pages=547–557|arxiv=astro-ph/0406559|bibcode=2004ApJ...614..547S|doi=10.1086/423607|s2cid=119010341}} Its redshift is 2.219. Other examples of quasars with large estimated black hole masses are the hyperluminous quasar APM 08279+5255, with an estimated mass of {{solar mass|{{val|1e10}} (10 billion)}},{{cite journal

| last1 = Saturni | first1 = F. G.

| last2 = Trevese | first2 = D.

| last3 = Vagnetti | first3 = F.

| last4 = Perna | first4 = M.

| last5 = Dadina | first5 = M.

| title = A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255. II. Emission- and absorption-line variability time lags

| year = 2016

| journal = Astronomy and Astrophysics

| volume = 587

| pages = A43

| doi = 10.1051/0004-6361/201527152

| arxiv = 1512.03195

| bibcode = 2016A&A...587A..43S

| s2cid = 118548618

}} and the quasar SMSS J215728.21-360215.1, with a mass of {{solar mass|{{val|3.4|0.6|e=10}} (34 billion)}}, or nearly 10,000 times the mass of the black hole at the Milky Way's Galactic Center.{{citation|title= thirty-four billion solar mass black hole in SMSS J2157–3602, the most luminous known quasar |journal=Monthly Notices of the Royal Astronomical Society |author=Christopher A Onken |author2=Fuyan Bian |author3=Xiaohui Fan |author4=Feige Wang |author5=Christian Wolf |author6=Jinyi Yang |date=August 2020|volume=496|issue=2|page=2309|doi=10.1093/mnras/staa1635|arxiv=2005.06868|bibcode=2020MNRAS.496.2309O|doi-access=free}}

Some galaxies, such as the galaxy 4C +37.11, appear to have two supermassive black holes at their centers, forming a binary system. If they collided, the event would create strong gravitational waves.{{cite web|last=Major|first=Jason|title=Watch what happens when two supermassive black holes collide|work=io9 |date=October 3, 2012 |url=http://io9.com/5948688/watch-what-happens-when-two-supermassive-black-holes-collide|publisher=Universe today|access-date=June 4, 2013}} Binary supermassive black holes are believed to be a common consequence of galactic mergers.{{cite web |first1=D. |last1=Merritt |first2=M. |last2=Milosavljevic |year=2005 |title=Massive Black Hole Binary Evolution |url=http://relativity.livingreviews.org/Articles/lrr-2005-8/ |access-date=March 3, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120330074938/http://relativity.livingreviews.org/Articles/lrr-2005-8/ |archive-date=March 30, 2012 |author1-link=David Merritt }} The binary pair in OJ 287, 3.5 billion light-years away, contains the most massive black hole in a pair, with a mass estimated at {{solar mass|18.348 billion}}.{{cite news| url=https://www.newscientist.com/article/dn13166-biggest-black-hole-in-the-cosmos-discovered.html|title= Biggest black hole in the cosmos discovered| date=January 10, 2008| work=New Scientist | first= David| last= Shiga}}{{Cite journal|arxiv =1208.0906 |last1 = Valtonen |first1 = M. J. |title = On the masses of OJ287 black holes |journal = Monthly Notices of the Royal Astronomical Society |volume = 427 |issue = 1 |pages = 77–83 |last2 = Ciprini |first2 = S. |last3 = Lehto |first3 = H. J. |year = 2012 |doi = 10.1111/j.1365-2966.2012.21861.x |doi-access = free |bibcode = 2012MNRAS.427...77V |s2cid = 118483466 }} In 2011, a super-massive black hole was discovered in the dwarf galaxy Henize 2-10, which has no bulge. The precise implications for this discovery on black hole formation are unknown, but may indicate that black holes formed before bulges.{{cite news|url=http://news.nationalgeographic.com/news/2011/01/110110-dwarf-galaxy-black-holes-universe-science-space/|archive-url=https://web.archive.org/web/20110112152607/http://news.nationalgeographic.com/news/2011/01/110110-dwarf-galaxy-black-holes-universe-science-space/|url-status=dead|archive-date=January 12, 2011|title=Huge Black Hole Found in Dwarf Galaxy|last=Kaufman|first=Rachel|date=January 10, 2011|work=National Geographic|access-date=June 1, 2011}}

File:A Black Hole’s Dinner is Fast Approaching - Part 2.ogv

In 2012, astronomers reported an unusually large mass of approximately {{solar mass|17 billion}} for the black hole in the compact, lenticular galaxy NGC 1277, which lies 220 million light-years away in the constellation Perseus. The putative black hole has approximately 59 percent of the mass of the bulge of this lenticular galaxy (14 percent of the total stellar mass of the galaxy).{{cite journal | last1 = van den Bosch | first1 = Remco C. E. | last2 = Gebhardt | first2 = Karl | last3 = Gültekin | first3 = Kayhan | last4 = van de Ven | first4 = Glenn | last5 = van der Wel | first5 = Arjen | last6 = Walsh | first6 = Jonelle L. | year = 2012| title = An over-massive black hole in the compact lenticular galaxy NGC 1277 | journal = Nature | volume = 491 | issue = 7426| pages = 729–731 | doi = 10.1038/nature11592 | pmid = 23192149 | arxiv = 1211.6429 | bibcode = 2012Natur.491..729V | s2cid = 205231230 }} Another study reached a very different conclusion: this black hole is not particularly overmassive, estimated at between {{solar mass|2 and 5 billion}} with {{solar mass|5 billion}} being the most likely value.{{cite journal |last=Emsellem |first= Eric|date=2013 |title=Is the black hole in NGC 1277 really overmassive? |journal=Monthly Notices of the Royal Astronomical Society |volume=433 |issue=3 |pages= 1862–1870 |doi= 10.1093/mnras/stt840 |doi-access= free|arxiv = 1305.3630 |bibcode = 2013MNRAS.433.1862E |s2cid= 54011632}}

On February 28, 2013, astronomers reported on the use of the NuSTAR satellite to accurately measure the spin of a supermassive black hole for the first time, in NGC 1365, reporting that the event horizon was spinning at almost the speed of light.{{Cite journal | last = Reynolds | first = Christopher | date = 2013 | title = Astrophysics: Black holes in a spin | journal = Nature | volume = 494 | issue = 7438 | pages = 432–433 | doi = 10.1038/494432a |bibcode = 2013Natur.494..432R | pmid=23446411| s2cid = 205076505 | doi-access = free }}{{Cite web | last = Prostak | first = Sergio | date = February 28, 2013 | title = Astronomers: Supermassive Black Hole in NGC 1365 Spins at Nearly Light-Speed | url = http://www.sci-news.com/astronomy/article00907.html | website = Sci-News.com | access-date = March 20, 2015 }}

In September 2014, data from different X-ray telescopes have shown that the extremely small, dense, ultracompact dwarf galaxy M60-UCD1 hosts a 20 million solar mass black hole at its center, accounting for more than 10% of the total mass of the galaxy. The discovery is quite surprising, since the black hole is five times more massive than the Milky Way's black hole despite the galaxy being less than five-thousandths the mass of the Milky Way.

Some galaxies 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 of at least {{val|e=10|u={{solar mass}}}}, despite the galaxy being one of the largest galaxies known; over six times the size and one thousand times the mass of the Milky Way. Despite that, several studies gave very large mass values for a possible central black hole inside A2261-BGC, such as about as large as {{val|6.5|10.9|4.1|e=10|u={{solar mass}}}} or as low as {{val|6|-|11|e=9|u={{solar mass}}}}. 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. This implies that either A2261-BGC has a central black hole that is accreting at a low level or has a mass rather below {{val|e=10|u={{solar mass}}}}.{{cite journal|arxiv=2010.13980|doi=10.3847/1538-4357/abc483 |title=Chandra Observations of Abell 2261 Brightest Cluster Galaxy, a Candidate Host to a Recoiling Black Hole |year=2021 |last1=Gültekin |first1=Kayhan |last2=Burke-Spolaor |first2=Sarah |last3=Lauer |first3=Tod R. |last4=w. Lazio |first4=T. Joseph |last5=Moustakas |first5=Leonidas A. |last6=Ogle |first6=Patrick |last7=Postman |first7=Marc |journal=The Astrophysical Journal |volume=906 |issue=1 |page=48 |bibcode=2021ApJ...906...48G |s2cid=225075966 |doi-access=free }}

In December 2017, astronomers reported the detection of the most distant quasar known by this time, ULAS J1342+0928, containing the most distant supermassive black hole, at a reported redshift of z = 7.54, surpassing the redshift of 7 for the previously known most distant quasar ULAS J1120+0641.{{cite journal |author=Bañados, Eduardo |display-authors=etal |title=An 800-million-solar-mass black hole in a significantly neutral Universe at a redshift of 7.5 |date=December 6, 2017 |journal=Nature |volume=553 |issue=7689 |pages=473–476 |doi=10.1038/nature25180 |pmid=29211709 |arxiv=1712.01860 |bibcode=2018Natur.553..473B |s2cid=205263326 }}{{cite web |last1=Landau |first1=Elizabeth |last2=Bañados |first2=Eduardo |title=Found: Most Distant Black Hole |url=https://www.jpl.nasa.gov/news/news.php?feature=7017 |date=December 6, 2017 |publisher=NASA |access-date=December 6, 2017 }}{{cite web |last=Choi |first=Charles Q. |title=Oldest Monster Black Hole Ever Found Is 800 Million Times More Massive Than the Sun |url=https://www.space.com/39000-oldest-farthest-monster-black-hole-yet.html |date=December 6, 2017 |work=Space.com |access-date=December 6, 2017 }}

{{multiple image

| header = Supermassive black hole and smaller black hole in galaxy OJ 287

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| image1 = SizesCompared-GalaxyOJ287CentralBlackHoles&SolarSystem.jpg

| caption1 = Comparisons of large and small black holes in galaxy OJ 287 to the Solar System

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| image2 = BlackHoleDiskFlareInGalaxyOJ287-animation-20200428.webm

| caption2 = Black hole disk flares in galaxy OJ 287
(1:22; animation; 28 April 2020)

| width2 = 400

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}}

File:Ophicus Explosion.jpg is responsible for the Ophiuchus Supercluster eruption – the most energetic eruption ever detected.
From: Chandra X-ray Observatory]]

In February 2020, astronomers reported the discovery of the Ophiuchus Supercluster eruption, the most energetic event in the Universe ever detected since the Big Bang.{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=This Black Hole Blew a Hole in the Cosmos – The galaxy cluster Ophiuchus was doing just fine until WISEA J171227.81-232210.7 — a black hole several billion times as massive as our sun — burped on it. |url=https://www.nytimes.com/2020/03/06/science/black-hole-cosmos-astrophysics.html |date=March 6, 2020 |work=The New York Times |access-date=March 6, 2020 }}{{cite web|url=https://www.theguardian.com/science/2020/feb/27/biggest-cosmic-explosion-ever-detected-makes-huge-dent-in-space|title=Biggest cosmic explosion ever detected left huge dent in space|date=February 27, 2020|access-date=March 6, 2020|work=The Guardian}}{{cite web|url=https://www.sciencedaily.com/releases/2020/02/200227114459.htm|title=Astronomers detect biggest explosion in the history of the Universe|date=February 27, 2020|access-date=March 6, 2020|work=Science Daily}} It occurred in the Ophiuchus Cluster in the galaxy NeVe 1, caused by the accretion of nearly {{solar mass|270 million}} of material by its central 7 billion {{Solar mass}} supermassive black hole.{{cite journal | bibcode=2021ApJ...914..121A | title=The NANOGrav 11 yr Data Set: Limits on Supermassive Black Hole Binaries in Galaxies within 500 MPC | last1=Arzoumanian | first1=Zaven | last2=Baker | first2=Paul T. | last3=Brazier | first3=Adam | last4=Brook | first4=Paul R. | last5=Burke-Spolaor | first5=Sarah | last6=Becsy | first6=Bence | last7=Charisi | first7=Maria | last8=Chatterjee | first8=Shami | last9=Cordes | first9=James M. | last10=Cornish | first10=Neil J. | last11=Crawford | first11=Fronefield | last12=Cromartie | first12=H. Thankful | last13=Decesar | first13=Megan E. | last14=Demorest | first14=Paul B. | last15=Dolch | first15=Timothy | last16=Elliott | first16=Rodney D. | last17=Ellis | first17=Justin A. | last18=Ferrara | first18=Elizabeth C. | last19=Fonseca | first19=Emmanuel | last20=Garver-Daniels | first20=Nathan | last21=Gentile | first21=Peter A. | last22=Good | first22=Deborah C. | last23=Hazboun | first23=Jeffrey S. | last24=Islo | first24=Kristina | last25=Jennings | first25=Ross J. | last26=Jones | first26=Megan L. | last27=Kaiser | first27=Andrew R. | last28=Kaplan | first28=David L. | last29=Kelley | first29=Luke Zoltan | last30=Key | first30=Joey Shapiro | journal=The Astrophysical Journal | date=2021 | volume=914 | issue=2 | page=121 | doi=10.3847/1538-4357/abfcd3 | doi-access=free | arxiv=2101.02716 | display-authors=1 }} The eruption lasted for about 100 million years and released 5.7 million times more energy than the most powerful gamma-ray burst known. The eruption released shock waves and jets of high-energy particles that punched the intracluster medium, creating a cavity about 1.5 million light-years wide – ten times the Milky Way's diameter.{{Cite journal|last1=Giacintucci|first1=S.|last2=Markevitch|first2=M.|last3=Johnston-Hollitt|first3=M.|last4=Wik|first4=D. R.|last5=Wang|first5=Q. H. S.|last6=Clarke|first6=T. E.|date=2020-02-27|title=Discovery of a giant radio fossil in the Ophiuchus galaxy cluster|journal=The Astrophysical Journal|volume=891|issue=1|pages=1|doi=10.3847/1538-4357/ab6a9d|issn=1538-4357|arxiv=2002.01291|bibcode=2020ApJ...891....1G|s2cid=211020555 |doi-access=free }}

In February 2021, astronomers released, for the first time, a very high-resolution image of 25,000 active supermassive black holes, covering four percent of the Northern celestial hemisphere, based on ultra-low radio wavelengths, as detected by the Low-Frequency Array (LOFAR) in Europe.{{cite news |last=Starr |first=Michelle |title=The White Dots in This Image Are Not Stars or Galaxies. They're Black Holes |url=https://www.sciencealert.com/every-white-dot-in-this-image-is-a-black-hole-at-the-heart-of-a-distant-galaxy |date=22 February 2021 |work=ScienceAlert |accessdate=22 February 2021 }}

{{div col}}

• {{annotated link|Black holes in fiction}}
• {{annotated link|Galactic Center GeV excess}}
• {{annotated link|Hypercompact stellar system}}
• {{annotated link|Spin-flip}}

{{div col end}}

{{Notelist|refs=

{{efn|name=sbh|The acronym SBH is commonly used for stellar-mass black hole.}}

}}

{{Reflist|refs=

{{cite journal | title=Constraints on Stupendously Large Black Holes | display-authors=1 | last1=Carr | first1=Bernard | last2=Kühnel | first2=Florian | last3=Visinelli | first3=Luca | journal=Monthly Notices of the Royal Astronomical Society | volume= 501 | issue=2 | pages=2029–2043 | date=February 2021 | doi=10.1093/mnras/staa3651 | doi-access=free | arxiv=2008.08077 | bibcode=2021MNRAS.501.2029C }}

}}

• {{Cite book |last=Fulvio Melia |title=The Edge of Infinity. Supermassive Black Holes in the Universe |date=2003 |publisher=Cambridge University Press |isbn=978-0-521-81405-8 |ol=22546388M}}
• {{Cite journal |last1=Carr |first1=Bernard |last2=Kühnel |first2=Florian |year=2022 |title=Primordial black holes as dark matter candidates |journal=SciPost Physics Lecture Notes |arxiv=2110.02821 |doi=10.21468/SciPostPhysLectNotes.48 |s2cid=238407875 |doi-access=free }}
• {{Cite journal |last1=Chakraborty |first1=Amlan |last2=Chanda |first2=Prolay K. |last3=Pandey |first3=Kanhaiya Lal |last4=Das |first4=Subinoy |year=2022 |title=Formation and Abundance of Late-forming Primordial Black Holes as Dark Matter |journal=The Astrophysical Journal |volume=932 |issue=2 |page=119 |arxiv=2204.09628 |bibcode=2022ApJ...932..119C |doi=10.3847/1538-4357/ac6ddd |s2cid=248266315 |doi-access=free }}
• {{Cite journal |last1=Ferrarese |first1=Laura |author-link=Laura Ferrarese |last2=Merritt |first2=David |author-link2=David Merritt |name-list-style=amp |date=2002 |title=Supermassive Black Holes |journal=Physics World |volume=15 |issue=1 |pages=41–46 |arxiv=astro-ph/0206222 |bibcode=2002astro.ph..6222F |doi=10.1088/2058-7058/15/6/43 |s2cid=5266031}}
• {{Cite book |last=Krolik |first=Julian |title=Active Galactic Nuclei |date=1999 |publisher=Princeton University Press |isbn=978-0-691-01151-6 |ol=361705M}}
• {{Cite book |last=Merritt |first=David |title=Dynamics and Evolution of Galactic Nuclei |date=2013 |publisher=Princeton University Press |isbn=978-0-691-12101-7 |author-link=David Merritt}}
• {{Cite journal|arxiv=1107.3562 |doi=10.1111/j.1365-2966.2011.19461.x |title=A lower limit on the halo mass to form supermassive black holes |date=2011 |last1=Dotan |first1=Calanit |last2=Rossi |first2=Elena M. |last3=Shaviv |first3=Nir J. |journal=Monthly Notices of the Royal Astronomical Society |volume=417 |issue=4 |pages=3035–3046 |doi-access=free |bibcode=2011MNRAS.417.3035D |s2cid=54854781 }}
• {{Cite journal|doi=10.1093/mnras/staa3986 |title=On the formation and stability of fermionic dark matter haloes in a cosmological framework |date=2021 |last1=Argüelles |first1=Carlos R. |last2=Díaz |first2=Manuel I. |last3=Krut |first3=Andreas |last4=Yunis |first4=Rafael |journal=Monthly Notices of the Royal Astronomical Society |volume=502 |issue=3 |pages=4227–4246 |doi-access=free |arxiv=2012.11709 }}
• {{Cite journal|arxiv=1604.03936 |doi=10.1093/mnras/stw2505 |title=Light or heavy supermassive black hole seeds: The role of internal rotation in the fate of supermassive stars |date=2017 |last1=Fiacconi |first1=Davide |last2=Rossi |first2=Elena M. |journal=Monthly Notices of the Royal Astronomical Society |volume=464 |issue=2 |pages=2259–2269 |doi-access=free }}
• {{Cite journal|doi=10.1186/s40668-018-0023-7 |doi-access=free |title=Observing supermassive black holes in virtual reality |date=2018 |last1=Davelaar |first1=Jordy |last2=Bronzwaer |first2=Thomas |last3=Kok |first3=Daniel |last4=Younsi |first4=Ziri |last5=Mościbrodzka |first5=Monika |last6=Falcke |first6=Heino |journal=Computational Astrophysics and Cosmology |volume=5 |issue=1 |page=1 |bibcode=2018ComAC...5....1D |arxiv=1811.08369 }}

{{Spoken Wikipedia|En-Supermassive_black_hole-article.ogg|date=2017-03-20}}

{{Wikinews category|Supermassive black holes}}

• [https://web.archive.org/web/20160706030802/http://hubblesite.org/explore_astronomy/black_holes/home.html Black Holes: Gravity's Relentless Pull] Interactive multimedia Web site about the physics and astronomy of black holes from the Space Telescope Science Institute
• [https://chandra.harvard.edu/photo/2002/0157/0157_composite.jpg Images of supermassive black holes]
• [https://apod.nasa.gov/apod/image/0210/mwcentre_eso_big.jpg NASA images of supermassive black holes]
• [https://web.archive.org/web/20160613034320/http://www.einstein-online.info/spotlights/milkyway_bh/?set_language=en The black hole at the heart of the Milky Way]
• [http://www.eso.org/public/videos/eso0846a/ ESO video clip of stars orbiting a galactic black hole]
• [https://web.archive.org/web/20051025013223/http://www.eso.org/outreach/press-rel/pr-2002/pr-17-02.html Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours] ESO, October 21, 2002
• [http://www.astro.ucla.edu/research/galcenter/ Images, Animations, and New Results from the UCLA Galactic Center Group]
• [https://www.washingtonpost.com/wp-dyn/content/article/2007/10/30/AR2007103002073.html?nav=most_emailed Washington Post article on Supermassive black holes]
• [https://www.youtube.com/watch?v=uVlcIb-rClI Video (2:46) – Simulation of stars orbiting Milky Way's central massive black hole]
• [https://www.youtube.com/watch?v=uDhDZi9Qxhk Video (2:13) – Simulation reveals supermassive black holes] (NASA, October 2, 2018)
• [https://www.nasa.gov/mission_pages/chandra/news/ultra_black_holes.html From Super to Ultra: Just How Big Can Black Holes Get?] {{Webarchive|url=https://web.archive.org/web/20190617101304/https://www.nasa.gov/mission_pages/chandra/news/ultra_black_holes.html |date=June 17, 2019 }}
• {{Cite web|last=September 2020|first=Paul Sutter 29|title=Black holes so big we don't know how they form could be hiding in the universe|url=https://www.space.com/ginormous-black-holes-could-lurk-in-universe.html|access-date=2021-02-06|website=Space.com|date=29 September 2020|language=en}}
• {{Cite web|url=https://www.eso.org/public/images/eventhorizon-shadows/ |title=Testing general relativity with a supermassive black hole }}
• {{Cite web|url=https://pweb.cfa.harvard.edu/news/wandering-black-holes |title=Wandering Black Holes | Center for Astrophysics }}
• {{Cite web|url=https://www.syfy.com/syfy-wire/supermassive-stars-might-be-born-in-the-chaos-around-supermassive-black-holes |title=Supermassive stars might be born in the chaos around supermassive black holes |date=May 10, 2021 }}

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