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Sagittarius A*

Sagittarius A* imaged by the Event Horizon Telescope in 2017, released in 2022
Observation data Epoch J2000      Equinox J2000
Constellation	Sagittarius
Right ascension	17 45 40.0409
Declination	−29° 0′ 28.118″
Details
Mass	8.54×10 kg 4.297×10 M☉
Astrometry
Distance	26996±33 ly (8277±9 pc)
Database references
SIMBAD	data

Sagittarius A*, abbreviated as Sgr A* (/ˈsædʒ ˈeɪ stɑːr/ SADGE-AY-star), is the supermassive black hole at the Galactic Center of the Milky Way. Viewed from Earth, it is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, visually close to the Butterfly Cluster (M6) and Lambda Scorpii.

The object is a bright and very compact astronomical radio source. The name Sagittarius A* distinguishes the compact source from the larger (and much brighter) Sagittarius A (Sgr A) region in which it is embedded. Sgr A* was discovered in 1974 by Bruce Balick [de] and Robert L. Brown, and the asterisk * was assigned in 1982 by Brown, who understood that the strongest radio emission from the center of the galaxy appeared to be due to a compact non-thermal radio object.

The observations of several stars orbiting Sagittarius A*, particularly star S2, have been used to determine the mass and upper limits on the radius of the object. Based on mass and increasingly precise radius limits, astronomers have concluded that Sagittarius A* must be the central supermassive black hole of the Milky Way galaxy. The current best estimate of its mass is 4.297±0.012 million solar masses.

Reinhard Genzel and Andrea Ghez were awarded the 2020 Nobel Prize in Physics for their discovery that Sagittarius A* is a supermassive compact object, for which a black hole was the only plausible explanation at the time.

In May 2022, astronomers released the first image of the accretion disk around the horizon of Sagittarius A*, confirming it to be a black hole, using the Event Horizon Telescope, a world-wide network of radio observatories. This is the second confirmed image of a black hole, after Messier 87's supermassive black hole in 2019. The black hole itself is not seen; as light is incapable of escaping the immense gravitational force of a black hole, only nearby objects whose behavior is influenced by the black hole can be observed. The observed radio and infrared energy emanates from gas and dust heated to millions of degrees while falling into the black hole.

Observation and description

On May 12, 2022, the first image of Sagittarius A* was released by the Event Horizon Telescope Collaboration. The image, which is based on radio interferometer data taken in 2017, confirms that the object contains a black hole. This is the second image of a black hole. This image took five years of calculations to process. The data was collected by eight radio observatories at six geographical sites. Radio images are produced from data by aperture synthesis, usually from night-long observations of stable sources. The radio emission from Sgr A* varies on the order of minutes, complicating the analysis.

Their result gives an overall angular size for the source of 51.8±2.3 μas. At a distance of 26,000 light-years (8,000 parsecs), this yields a diameter of 51.8 million kilometres (32.2 million miles). For comparison, Earth is 150 million kilometres (1.0 astronomical unit; 93 million miles) from the Sun, and Mercury is 46 million km (0.31 AU; 29 million mi) from the Sun at perihelion. The proper motion of Sgr A* is approximately −2.70 mas per year for the right ascension and −5.6 mas per year for the declination. The telescope's measurement of these black holes tested Einstein's theory of relativity more rigorously than has previously been done, and the results match perfectly.

In 2019, measurements made with the High-resolution Airborne Wideband Camera-Plus (HAWC+) mounted in the SOFIA aircraft revealed that magnetic fields cause the surrounding ring of gas and dust, temperatures of which range from −280 to 17,500 °F (99.8 to 9,977.6 K; −173.3 to 9,704.4 °C), to flow into an orbit around Sagittarius A*, keeping black hole emissions low.

Astronomers have been unable to observe Sgr A* in the optical spectrum because of the effect of 25 magnitudes of extinction (absorption and scattering) by dust and gas between the source and Earth.

History

In April 1933, Karl Jansky, considered one of the fathers of radio astronomy, discovered that a radio signal was coming from a location in the direction of the constellation of Sagittarius, towards the center of the Milky Way. The radio source later became known as Sagittarius A. His observations did not extend quite as far south as we now know to be the Galactic Center. Observations by Jack Piddington and Harry Minnett using the CSIRO radio telescope at Potts Hill Reservoir, in Sydney discovered a discrete and bright "Sagittarius-Scorpius" radio source, which after further observation with the 80-foot (24-metre) CSIRO radio telescope at Dover Heights was identified in a letter to Nature as the probable Galactic Center.

Later observations showed that Sagittarius A actually consists of several overlapping sub-components; a bright and very compact component, Sgr A*, was discovered on February 13 and 15, 1974, by Balick and Robert L Brown using the baseline interferometer of the National Radio Astronomy Observatory. The name Sgr A* was coined by Brown in a 1982 paper because the radio source was "exciting", and excited states of atoms are denoted with asterisks.

Since the 1980s, it has been evident that the central component of Sgr A* is likely a black hole. In 1994, infrared and sub-millimetre spectroscopy studies by a Berkeley team involving Nobel Laureate Charles H. Townes and future Nobel Prize Winner Reinhard Genzel showed that the mass of Sgr A* was tightly concentrated and on the order of 3 million Suns.

On October 16, 2002, an international team led by Reinhard Genzel at the Max Planck Institute for Extraterrestrial Physics reported the observation of the motion of the star S2 near Sagittarius A* throughout a period of ten years. According to the team's analysis, the data ruled out the possibility that Sgr A* contains a cluster of dark stellar objects or a mass of degenerate fermions, strengthening the evidence for a massive black hole. The observations of S2 used near-infrared (NIR) interferometry (in the Ks-band, i.e. 2.1 μm) because of reduced interstellar extinction in this band. SiO masers were used to align NIR images with radio observations, as they can be observed in both NIR and radio bands. The rapid motion of S2 (and other nearby stars) easily stood out against slower-moving stars along the line-of-sight so these could be subtracted from the images.

The VLBI radio observations of Sagittarius A* could also be aligned centrally with the NIR images, so the focus of S2's elliptical orbit was found to coincide with the position of Sagittarius A*. From examining the Keplerian orbit of S2, they determined the mass of Sagittarius A* to be 4.1±0.6 million solar masses, confined in a volume with a radius no more than 17 light-hours (120 AU ). Later observations of the star S14 showed the mass of the object to be about 4.1 million solar masses within a volume with radius no larger than 6.25 light-hours (45 AU ). S175 passed within a similar distance. For comparison, the Schwarzschild radius is 0.08 AU (12 million km; 7.4 million mi). They also determined the distance from Earth to the Galactic Center (the rotational center of the Milky Way), which is important in calibrating astronomical distance scales, as 8,000 ± 600 parsecs (30,000 ± 2,000 light-years). In November 2004, a team of astronomers reported the discovery of a potential intermediate-mass black hole, referred to as GCIRS 13E, orbiting 3 light-years from Sagittarius A*. This black hole of 1,300 solar masses is within a cluster of seven stars. This observation may add support to the idea that supermassive black holes grow by absorbing nearby smaller black holes and stars.

After monitoring stellar orbits around Sagittarius A* for 16 years, Gillessen et al. estimated the object's mass at 4.31±0.38 million solar masses. The result was announced in 2008 and published in The Astrophysical Journal in 2009. Reinhard Genzel, team leader of the research, said the study has delivered "what is now considered to be the best empirical evidence that supermassive black holes do really exist. The stellar orbits in the Galactic Center show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt."

On January 5, 2015, NASA reported observing an X-ray flare 400 times brighter than usual, a record-breaker, from Sgr 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 Sgr A*, according to astronomers.

On 13 May 2019, astronomers using the Keck Observatory witnessed a sudden brightening of Sgr A*, which became 75 times brighter than usual, suggesting that the supermassive black hole may have encountered another object.

In June 2023, unexplained filaments of radio energy were found associated with Sagittarius A*.

• ALMA observations of molecular-hydrogen-rich gas clouds, with the area around Sagittarius A* circled
• An unusually bright X-ray flare from Sgr A* was detected in 2013.
• Supernova remnant ejecta producing planet-forming material seen in radio and X-ray
• Supernova remnant ejecta producing planet-forming material seen in infrared and X-ray

Central black hole

In a paper published on October 31, 2018, the discovery of conclusive evidence that Sagittarius A* is a black hole was announced. Using the GRAVITY interferometer and the four telescopes of the Very Large Telescope (VLT) to create a virtual telescope 130 metres (430 feet) in diameter, astronomers detected clumps of gas moving at about 30% of the speed of light. Emission from highly energetic electrons very close to the black hole was visible as three prominent bright flares. These exactly match theoretical predictions for hot spots orbiting close to a black hole of four million solar masses. The flares are thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*.

In July 2018, it was reported that S2 orbiting Sgr A* had been recorded at 7,650 km/s (17.1 million mph), or 2.55% the speed of light, leading up to the pericenter approach, in May 2018, at about 120 AU (18 billion km; 11 billion mi) (approximately 1,400 Schwarzschild radii) from Sgr A*. At that close distance to the black hole, Einstein's theory of general relativity (GR) predicts that S2 would show a discernible gravitational redshift in addition to the usual velocity redshift; the gravitational redshift was detected, in agreement with the GR prediction within the 10 percent measurement precision.

Assuming that general relativity is still a valid description of gravity near the event horizon, the Sagittarius A* radio emissions are not centered on the black hole, but arise from a bright spot in the region around the black hole, close to the event horizon, possibly in the accretion disc, or a relativistic jet of material ejected from the disc. If the apparent position of Sagittarius A* were exactly centered on the black hole, it would be possible to see it magnified beyond its size, because of gravitational lensing of the black hole. According to general relativity, this would result in a ring-like structure, which has a diameter about 5.2 times the black hole's Schwarzschild radius (10 μas). For a black hole of around 4 million solar masses, this corresponds to a size of approximately 52 μas, which is consistent with the observed overall size of about 50 μas, the size (apparent diameter) of the black hole Sgr A* itself being 20 μas.

Recent lower resolution observations revealed that the radio source of Sagittarius A* is symmetrical. Simulations of alternative theories of gravity depict results that may be difficult to distinguish from GR. However, a 2018 paper predicts an image of Sagittarius A* that is in agreement with recent observations; in particular, it explains the small angular size and the symmetrical morphology of the source.

The mass of Sagittarius A* has been estimated in two different ways:

1. Two groups—in Germany and the U.S.—monitored the orbits of individual stars very near to the black hole and used Kepler's laws to infer the enclosed mass. The German group found a mass of 4.31±0.38 million solar masses, whereas the American group found 4.1±0.6 million solar masses. Given that this mass is confined inside a 44-million-kilometre-diameter sphere, this yields a density ten times higher than previous estimates.
2. More recently, measurement of the proper motions of a sample of several thousand stars within approximately one parsec from the black hole, combined with a statistical technique, has yielded both an estimate of the black hole's mass at 3.6+0.2
   −0.4×10 M_☉, plus a distributed mass in the central parsec amounting to (1±0.5)×10 M_☉. The latter is thought to be composed of stars and stellar remnants.

The comparatively small mass of this supermassive black hole, along with the low luminosity of the radio and infrared emission lines, imply that the Milky Way is not a Seyfert galaxy.

Ultimately, what is seen is not the black hole itself, but observations that are consistent only if there is a black hole present near Sgr A*. In the case of such a black hole, the observed radio and infrared energy emanates from gas and dust heated to millions of degrees while falling into the black hole. The black hole itself is thought to emit only Hawking radiation at a negligible temperature, on the order of 10 kelvin.

The European Space Agency's gamma-ray observatory INTEGRAL observed gamma rays interacting with the nearby giant molecular cloud Sagittarius B2, causing X-ray emission from the cloud. The total luminosity from this outburst (L≈1,5×10 erg/s) is estimated to be a million times stronger than the current output from Sgr A* and is comparable with a typical active galactic nucleus. In 2011 this conclusion was supported by Japanese astronomers observing the Milky Way's center with the Suzaku satellite.

In July 2019, astronomers reported finding a star, S5-HVS1, traveling 1,755 km/s (3.93 million mph) or 0.006 c. The star is in the Grus (or Crane) constellation in the southern sky, and about 29,000 light-years from Earth, and may have been propelled out of the Milky Way galaxy after interacting with Sagittarius A*.

Several values have been given for its spin parameter ${\displaystyle a_{*}={\frac {cJ}{GM^{2}}}}$; some examples are Fragione & Loeb (2020) ${\displaystyle a_{*}<0.1}$, Belanger et al. (2006) ${\displaystyle a_{*}\sim 0.22}$, Meyer et al. (2006) ${\displaystyle a_{*}>0.4}$, Genzel et al. (2003) ${\displaystyle a_{*}\sim 0.52}$, Daly (2019) ${\displaystyle a_{*}=0.93\pm 0.15}$, , and Daly et al. (2023) ${\displaystyle a_{*}=0.90\pm 0.06}$. Daly et al. (2023) also found that the ratio of the black hole rotational mass component to the irreducible mass component of Sgr A* is ${\displaystyle M_{rot}/M_{irr}=0.62\pm 0.10}$, which indicates that the black hole is rotating with an angular velocity that is ${\displaystyle 0.62\pm 0.10}$ of the maximum possible value, set by the speed of light.

Orbiting stars

There are a number of stars in close orbit around Sagittarius A*, which are collectively known as "S stars". These stars are observed primarily in K band infrared wavelengths, as interstellar dust drastically limits visibility in visible wavelengths. This is a rapidly changing field—in 2011, the orbits of the most prominent stars then known were plotted in the diagram at left, showing a comparison between their orbits and various orbits in the solar system. Since then, S62 has been found to approach even more closely than those stars.

The high velocities and close approaches to the supermassive black hole makes these stars useful to establish limits on the physical dimensions of Sagittarius A*, as well as to observe general-relativity associated effects like periapse shift of their orbits. An active watch is maintained for the possibility of stars approaching the event horizon close enough to be disrupted, but none of these stars are expected to suffer that fate.

As of 2020, S4714 is the current record holder of closest approach to Sagittarius A*, at about 12.6 AU (1.88 billion km), almost as close as Saturn gets to the Sun, traveling at about 8% of the speed of light. These figures given are approximate, the formal uncertainties being 12.6±9.3 AU and 23,928±8,840 km/s. Its orbital period is 12 years, but an extreme eccentricity of 0.985 gives it the close approach and high velocity.

An excerpt from a table of this cluster (see Sagittarius A* cluster), featuring the most prominent members. In the below table, id1 is the star's name in the Gillessen catalog and id2 in the catalog of the University of California, Los Angeles. a, e, i, Ω and ω are standard orbital elements, with a measured in arcseconds. Tp is the epoch of pericenter passage, P is the orbital period in years and Kmag is the infrared K-band apparent magnitude of the star. q and v are the pericenter distance in AU and pericenter speed in percent of the speed of light.

Discovery of G2 gas cloud on an accretion course

First noticed as something unusual in images of the center of the Milky Way in 2002, the gas cloud G2, which has a mass about three times that of Earth, was confirmed to be likely on a course taking it into the accretion zone of Sgr A* in a paper published in Nature in 2012. Predictions of its orbit suggested it would make its closest approach to the black hole (a perinigricon) in early 2014, when the cloud was at a distance of just over 3,000 times the radius of the event horizon (or ≈260 AU, 36 light-hours) from the black hole. G2 has been observed to be disrupting since 2009, and was predicted by some to be completely destroyed by the encounter, which could have led to a significant brightening of X-ray and other emission from the black hole. Other astronomers suggested the gas cloud could be hiding a dim star, or a binary star merger product, which would hold it together against the tidal forces of Sgr A*, allowing the ensemble to pass by without any effect. In addition to the tidal effects on the cloud itself, it was proposed in May 2013 that, prior to its perinigricon, G2 might experience multiple close encounters with members of the black-hole and neutron-star populations thought to orbit near the Galactic Center, offering some insight to the region surrounding the supermassive black hole at the center of the Milky Way.

The average rate of accretion onto Sgr A* is unusually small for a black hole of its mass and is only detectable because it is so close to Earth. It was thought that the passage of G2 in 2013 might offer astronomers the chance to learn much more about how material accretes onto supermassive black holes. Several astronomical facilities observed this closest approach, with observations confirmed with Chandra, XMM, VLA, INTEGRAL, Swift, Fermi and requested at VLT and Keck.

Simulations of the passage were made before it happened by groups at ESO and Lawrence Livermore National Laboratory (LLNL).

As the cloud approached the black hole, Daryl Haggard said, "It's exciting to have something that feels more like an experiment", and hoped that the interaction would produce effects that would provide new information and insights.

Nothing was observed during and after the closest approach of the cloud to the black hole, which was described as a lack of "fireworks" and a "flop". Astronomers from the UCLA Galactic Center Group published observations obtained on March 19 and 20, 2014, concluding that G2 was still intact (in contrast to predictions for a simple gas cloud hypothesis) and that the cloud was likely to have a central star.

An analysis published on July 21, 2014, based on observations by the ESO's Very Large Telescope in Chile, concluded alternatively that the cloud, rather than being isolated, might be a dense clump within a continuous but thinner stream of matter, and would act as a constant breeze on the disk of matter orbiting the black hole, rather than sudden gusts that would have caused high brightness as they hit, as originally expected. Supporting this hypothesis, G1, a cloud that passed near the black hole 13 years ago, had an orbit almost identical to G2, consistent with both clouds, and a gas tail thought to be trailing G2, all being denser clumps within a large single gas stream.

Andrea Ghez et al. suggested in 2014 that G2 is not a gas cloud but rather a pair of binary stars that had been orbiting the black hole in tandem and merged into an extremely large star.

See also

• Galactic Center GeV excess – Unexplained gamma rays from the Galactic Center
• List of nearest known black holes

Notes

1. This roughly equates to around 37 times the diameter of the Sun at ~1,400,000 kilometers (~865,000 miles).

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Further reading

• Backer, D. C. & Sramek, R. A. (October 20, 1999). "Proper Motion of the Compact, Nonthermal Radio Source in the Galactic Center, Sagittarius A*". The Astrophysical Journal. 524 (2): 805–815. arXiv:astro-ph/9906048. Bibcode:1999ApJ...524..805B. doi:10.1086/307857. ISSN 0004-637X. S2CID 18858138.
• Gillessen, Stefan; et al. (February 23, 2009). "Monitoring stellar orbits around the Massive Black Hole in the Galactic Center". The Astrophysical Journal. 692 (2): 1075–1109. arXiv:0810.4674. Bibcode:2009ApJ...692.1075G. doi:10.1088/0004-637X/692/2/1075. S2CID 1431308.
• Melia, Fulvio (2007). The galactic supermassive black hole. Princeton: Princeton Univ. ISBN 978-0-691-13129-0.
• O'Neill, Ian (December 10, 2008). "Beyond Any Reasonable Doubt: A Supermassive Black Hole Lives in Centre of Our Galaxy". Universe Today.
• Osterbrock, Donald E. & Ferland, Gary J. (2006). Astrophysics of gaseous nebulae and active galactic nuclei (2nd ed.). Mill Valley, California: University Science Books. ISBN 978-1-891389-34-4.
• Reid, M. J.; Brunthaler, A. (December 2004). "The Proper Motion of Sagittarius A*. II. The Mass of Sagittarius A*". The Astrophysical Journal. 616 (2): 872–884. arXiv:astro-ph/0408107. Bibcode:2004ApJ...616..872R. doi:10.1086/424960. ISSN 0004-637X. S2CID 16568545.
• Schödel, R.; et al. (October 2002). "A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way". Nature. 419 (6908): 694–696. arXiv:astro-ph/0210426. Bibcode:2002Natur.419..694S. doi:10.1038/nature01121. ISSN 0028-0836. PMID 12384690. S2CID 4302128.
• Schödel, R.; Merritt, D.; Eckart, A. (July 2009). "The nuclear star cluster of the Milky Way: proper motions and mass". Astronomy & Astrophysics. 502 (1): 91–111. arXiv:0902.3892. Bibcode:2009A&A...502...91S. doi:10.1051/0004-6361/200810922. ISSN 0004-6361. S2CID 219559.
• Melia, Fulvio (2003). The black hole at the center of our galaxy. Princeton: Princeton University Press. ISBN 978-0-691-09505-9.
• Doeleman, Sheperd S.; et al. (September 2008). "Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre". Nature. 455 (7209): 78–80. arXiv:0809.2442. Bibcode:2008Natur.455...78D. doi:10.1038/nature07245. ISSN 0028-0836. PMID 18769434. S2CID 4424735.
• Eckart, Andreas; Schödel, Rainer; Straubmeier, Christian Michael; Straubmeier, Christian (2005). The black hole at the center of the Milky Way. London: Imperial College Press. ISBN 978-1-86094-567-0.
• Eisenhauer, F.; Schdel, R.; Genzel, R.; Ott, T.; Tecza, M.; Abuter, R.; Eckart, A.; Alexander, T.; et al. (November 10, 2003). "A Geometric Determination of the Distance to the Galactic Center". The Astrophysical Journal. 597 (2): L121–L124. arXiv:astro-ph/0306220. Bibcode:2003ApJ...597L.121E. doi:10.1086/380188. ISSN 0004-637X. S2CID 16425333.
• The Event Horizon Telescope Collaboration (April 10, 2019). "First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole". The Astrophysical Journal Letters. 875 (1): L1. arXiv:1906.11238. Bibcode:2019ApJ...875L...1E. doi:10.3847/2041-8213/ab0ec7. S2CID 145906806.
• Ghez, A. M.; et al. (April 1, 2003). "The First Measurement of Spectral Lines in a Short-Period Star Bound to the Galaxy's Central Black Hole: A Paradox of Youth". The Astrophysical Journal. 586 (2): L127–L131. arXiv:astro-ph/0302299. Bibcode:2003ApJ...586L.127G. doi:10.1086/374804. S2CID 11388341.
• Ghez, A. M.; et al. (December 20, 2008). "Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits". The Astrophysical Journal. 689 (2): 1044–1062. arXiv:0808.2870. Bibcode:2008ApJ...689.1044G. doi:10.1086/592738. ISSN 0004-637X. S2CID 18335611.
• Reynolds, Christopher S. (September 2008). "Bringing black holes into focus". Nature. 455 (7209): 39–40. Bibcode:2008Natur.455...39R. doi:10.1038/455039a. ISSN 0028-0836. PMID 18769426. S2CID 205040663.
• Wheeler, J. Craig (2007). Cosmic catastrophes: exploding stars, black holes, and mapping the universe (2nd ed.). Cambridge ; New York: Cambridge University Press. ISBN 978-0-521-85714-7. OCLC 73954922.
• Banner, Tanja (March 2, 2023). "Eigentlich dürfte er nicht existieren: Babystern nah an schwarzem Loch entdeckt". Frankfurter Rundschau (in German). Retrieved March 2, 2023.
• Peißker, F.; Zajaček, M.; Melamed, M.; Ali, B.; Singhal, M.; Dassel, T.; Eckart, A.; Karas, V. (June 2024). "Candidate young stellar objects in the S-cluster: Kinematic analysis of a subpopulation of the low-mass G objects close to Sgr A*". Astronomy & Astrophysics. 686: A235. arXiv:2406.09916. Bibcode:2024A&A...686A.235P. doi:10.1051/0004-6361/202449729. ISSN 0004-6361.
• Rayne, Elizabeth (July 4, 2024). "Swarm of dusty young stars found around our galaxy's central black hole". Ars Technica. Retrieved July 5, 2024.

External links

• Is there a Supermassive Black Hole at the Center of the Milky Way? (arXiv preprint)
• 2004 paper deducing mass of central black hole from orbits of 7 stars (arXiv preprint)
• ESO video clip of orbiting star (533 KB MPEG Video)
• The Proper Motion of Sgr A* and the Mass of Sgr A* (PDF)
• NRAO article regarding VLBI radio imaging of Sgr A*
• Peering into a Black Hole, 2015 New York Times video
• Image of supermassive black hole Sagittarius A* (2022), Harvard Center for Astrophysics
• Video (65:30) – EHT conference presenting first image of Sgr A* on YouTube (NSF; 12 May 2022)

v t e Black holes
Outline
Types	BTZ black hole Schwarzschild Rotating Charged Virtual Kugelblitz Supermassive Primordial Direct collapse Rogue Malament–Hogarth spacetime
Size	Micro Extremal Electron Stellar Microquasar Intermediate-mass Supermassive Active galactic nucleus Quasar LQG Blazar OVV
Formation	Stellar evolution Gravitational collapse Neutron star Related links Tolman–Oppenheimer–Volkoff limit White dwarf Related links Supernova Micronova Hypernova Related links Gamma-ray burst Binary black hole Quark star Supermassive star Quasi-star Supermassive dark star X-ray binary
Properties	Astrophysical jet Gravitational singularity Ring singularity Theorems Event horizon Photon sphere Innermost stable circular orbit Ergosphere Penrose process Blandford–Znajek process Accretion disk Hawking radiation Gravitational lens Microlens Bondi accretion M–sigma relation Quasi-periodic oscillation Thermodynamics Bekenstein bound Bousso's holographic bound Immirzi parameter Schwarzschild radius Spaghettification
Issues	Black hole complementarity Information paradox Cosmic censorship ER = EPR Final parsec problem Firewall (physics) Holographic principle No-hair theorem
Metrics	Schwarzschild (Derivation) Kerr Reissner–Nordström Kerr–Newman Hayward
Alternatives	Nonsingular black hole models Black star Dark star Dark-energy star Gravastar Magnetospheric eternally collapsing object Planck star Q star Fuzzball Geon
Analogs	Optical black hole Sonic black hole
Lists	Black holes Most massive Nearest Quasars Microquasars
Related	Outline of black holes Black Hole Initiative Black hole starship Black holes in fiction Big Bang Big Bounce Compact star Exotic star Quark star Preon star Gravitational waves Gamma-ray burst progenitors Gravity well Hypercompact stellar system Membrane paradigm Naked singularity Population III star Supermassive star Quasi-star Supermassive dark star Rossi X-ray Timing Explorer Superluminal motion Timeline of black hole physics White hole Wormhole Tidal disruption event Planet Nine
Notable	Cygnus X-1 XTE J1650-500 XTE J1118+480 A0620-00 Sagittarius A* Centaurus A Phoenix Cluster PKS 1302-102 OJ 287 SDSS J0849+1114 TON 618 MS 0735.6+7421 NeVe 1 Hercules A 3C 273 Q0906+6930 Markarian 501 ULAS J1342+0928 PSO J030947.49+271757.31 AT2018hyz Swift J1644+57
Category Commons

v t e Milky Way
Location	Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow (→) may be read as "within" or "part of".
Structure	Galactic Center Sagittarius A Sagittarius A* Fermi bubbles Supermassive black hole Galactic Center filaments Disk Carina–Sagittarius Norma–Cygnus Orion–Cygnus Perseus Scutum–Centaurus Near 3 kpc Arm Far 3 kpc Arm Halo Aquarius Stream Fimbulthul stream Gaia Sausage Helmi stream Magellanic Stream Monoceros Ring Palomar 5 stream Pisces-Eridanus stream Sagittarius Stream Virgo Stream
Satellite galaxies	Magellanic Clouds Large Magellanic Cloud Small Magellanic Cloud Magellanic Bridge Dwarfs Antlia II Boötes I Boötes II Boötes III Canes Venatici I Canes Venatici II Canis Major Carina Coma Berenices Crater 2 Draco Eridanus II Fornax Hercules Leo I Leo II Leo IV Leo V Leo T Phoenix Pisces Overdensity Pisces II Reticulum II Sagittarius Spheroidal Segue 1 Segue 2 Sculptor Sextans Triangulum II Ursa Major I Ursa Major II Ursa Major III Ursa Minor Virgo I Willman 1
Related	Alternate names Andromeda–Milky Way collision Baade's Window In mythology Zone of Avoidance
Astronomy portal Category

v t e Constellation of Sagittarius
List of stars in Sagittarius Galactic Center Central Molecular Zone Large Sagittarius Star Cloud Sagittarius in Chinese astronomy Wow! signal
Stars	Bayer α (Rukbat) β (Arkab Prior) β (Arkab Posterior) γ (W) γ (Alnasl) δ (Kaus Media) ε (Kaus Australis) ζ (Ascella) η θ θ ι κ κ λ (Kaus Borealis) μ (Polis) ν (Ainalrami) ν ξ ξ ο π (Albaldah) ρ ρ σ (Nunki) τ υ φ χ χ χ ψ ω (Terebellum) Flamsteed 1 4 5 6 7 9 12 14 15 16 17 18 21 23 24 25 26 28 29 30 31 33 43 (d) 50 51 (h) 52 (h) 53 54 (e) 55 (e) 56 (f) 57 59 (b) 60 (A) 61 (g) 62 (c) 63 65 63 Oph Variable T U X (3) Y RR RS RY RZ VX VY VZ WZ XX XZ YY YZ AQ AS AV BB FN GM GU KW MV V348 V350 V356 V440 V505 V523 V526 V617 V630 V725 V732 V774 V919 V1017 V1059 V1216 V1223 V1647 V1942 V3792 V3795 V3804 V3879 V3885 V3890 V3892 V3894 V3903 (11) V3961 V3984 V4021 V4024 V4028 V4029 V4030 V4046 V4050 V4064 V4072 V4089 V4091 V4138 V4140 V4160 V4169 V4190 V4198 V4199 V4200 V4332 V4333 V4334 V4371 V4375 V4381 V4387 V4405 V4407 V4434 V4444 V4580 V4633 V4641 V4647 (Pistol Star) V4650 V4728 V4743 V4745 V4998 V5112 V5115 V5116 V5125 V5157 V5555 V5558 V5652 V5668 V5856 HR 6617 6679 6680 6691 6692 6693 6704 6716 6739 6748 6762 6766 6769 6777 6780 6788 6798 6835 6836 6838 6842 6864 6874 6889 6907 6909 6914 6919 6933 6936 6944 6960 6972 6988 6990 6998 7026 7029 7035 7038 7072 7104 7126 7128 7151 7159 7164 7166 7168 7182 7186 7195 7203 7205 7211 7230 7239 7240 7246 7265 7276 7277 7282 7316 7317 7327 7330 7334 7350 7355 7360 7367 7378 7380 7392 7398 7410 7433 7443 7454 7473 7491 7496 7507 7532 7538 7585 7616 7627 7629 7630 7631 7639 7643 7652 7658 7659 7703 7706 7725 7765 7799 7801 7808 HD 163296 163758 164604 (Pincoya) 164816 165052 169142 170657 171238 175390 175754 177765 180902 181342 181720 183577 187085 187150 190647 313846 316285 Other 2MASS 19281982-2640123 2MASS J18352154–3123385 2MASS J19513587-3510375 4U 1755-33 4U 1820-30 A1742-294 Ap 1-11 AS 295 BD -18 5550 Bursting Pulsar CWISEP J1935-1546 GCIRS 13E 745 GGD 27 GRO J1744−28 GRS 1758-258 GS 1826-24 GX 3-1 GX 5-1 GX 9-1 GX 13+1 HATS-36 Herschel 36 HETE J1900.1-2455 IRAS 17423-1755 IRAS 18162−2048 GCIRS 3 GCIRS 7 GCIRS 8* GCIRS 16SW Gomez's Hamburger G0.238-0.071 K2-2016-BLG-0005L LBV 1806-20 LS IV -12 111 MACHO 176.18833.411 MACHO-1997-BLG-41 MACHO-98-BLG-35 NGC 6822-WR 12 PSR B1744−24A PSR B1749−28 PSR B1757−24 PSR B1758−23 PSR B1800−21 PSR B1821−24 PSR B1857−26 PSR J1808−2024 PSR J1747−2958 PSR J1748−2446ad S2 S55 S62 S4716 SAX J1747.0−2853 SAX J1808.4−3658 SAX J1810.8−2609 SWEEPS J175853.92−291120.6 SWEEPS J175902.00-291323.7 SWEEPS J175902.67−291153.5 Swift J1745-26 SWIFT J1756.9−2508 Th 4-4 W33A WASP-67 WD 0032−317 WR 102 c ea ka WR 101-2 WR 104 WR 110 WR 111 WR 112 XTE J1748−288 XTE J1807−294 XTE J1810−197 XTE J1814−338
Exoplanets HATS-36b HD 164604 b HD 181720 b K2-2016-BLG-0005Lb KMT-2022-BLG-0440L b MOA-2007-BLG-192Lb MOA-2007-BLG-400Lb MOA-2009-BLG-387Lb MOA-2010-BLG-477Lb OGLE-2003-BLG-235Lb OGLE-2005-BLG-169Lb OGLE-2018-BLG-1119Lb OGLE-TR-10b OGLE-TR-56b SWIFT J1756.9-2508 b
Star clusters	NGC NGC 6440 NGC 6520 NGC 6522 NGC 6528 NGC 6530 NGC 6540 NGC 6544 NGC 6553 NGC 6558 NGC 6569 NGC 6603 NGC 6624 NGC 6638 NGC 6642 NGC 6717 NGC 6723 Other 1806−20 cluster 2MASS-GC02 Arches Cluster CO-0.40-0.22 Messier 18 Messier 21 Messier 22 Messier 23 Messier 25 Messier 28 Messier 54 Messier 55 Messier 69 Messier 70 Messier 75 Quintuplet cluster Small Sagittarius Star Cloud
Nebulae	NGC NGC 6822 (Bubble Nebula) NGC 6445 NGC 6559 NGC 6563 NGC 6565 NGC 6578 NGC 6589 NGC 6590 NGC 6818 Other Barnard 92 G1.9+0.3 HCN-0.009-0.044 Lagoon Nebula Large Molecule Heimat M 1-42 M2-42 Omega Nebula Pistol Nebula Red Spider Nebula Ring Nebula Trifid Nebula
Galaxies	NGC NGC 6822 NGC 6902 Other MRC 2011-298 PKS 1830-211 PKS 2000-330 PKS 2004-447 Sagittarius Dwarf Irregular Galaxy Sagittarius Dwarf Spheroidal Galaxy
Galaxy clusters ESO 593-8
Astronomical events GLEAM-X J162759.5−523504.3 MOA-2007-BLG-192L MOA-2007-BLG-400L MOA-2009-BLG-387L MOA-2010-BLG-477L MOA-2011-BLG-262L OGLE-2003-BLG-235L OGLE-2005-BLG-169L Nova Sagittarii 1982
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• Astronomical objects discovered in 1974
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