| 词条 | Sagittarius A* | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 释义 |
| epoch=J2000 | constell=Sagittarius | ra={{RA|17|45|40.0409}} | dec={{DEC|−29|0|28.118}}[1] }}{{Starbox detail | mass = (4.31 ± 0.38) × 106[2]{{Solar mass|link=y}} (4.1 ± 0.6) × 106[2]{{Solar mass|link=y}} (4.02 ± 0.16) × 106[3] }}{{Starbox astrometry | dist_pc=7,860±140±40[3] }}{{Starbox reference |Simbad=NAME+Sgr+A* }}{{Starbox end}} Sagittarius A* (pronounced "Sagittarius A-star", standard abbreviation Sgr A*) is a bright and very compact astronomical radio source at the center of the Milky Way, near the border of the constellations Sagittarius and Scorpius. It is part of a larger astronomical feature known as Sagittarius A. Sagittarius A* is the location of a supermassive black hole,[4][5][6] like those that are now generally accepted to be at the centers of most if not all spiral and elliptical galaxies. Observations of a number of stars, most notably the star S2, orbiting around Sagittarius A* have been used to show the presence of, and produce data about, the Milky Way's central supermassive black hole, and have led to the conclusion that Sagittarius A* is the site of that black hole.[7] Observation and descriptionAstronomers have been unable to observe Sgr A* in the optical spectrum because of the effect of 25 magnitudes of extinction by dust and gas between the source and Earth.[9] Several teams of researchers have attempted to image Sagittarius A* in the radio spectrum using very-long-baseline interferometry (VLBI).[10] The current highest-resolution (approximately 30 μas) measurement, made at a wavelength of 1.3 mm, indicated an overall angular size for the source of 50μas.[13] At a distance of 26,000 light-years, this yields a diameter of 60 million kilometers. For comparison, Earth is 150 million kilometers from the Sun, and Mercury is 46 million kilometers 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.[11] In 2016 direct radio images were taken of Sagittarius A* by the Event Horizon Telescope, but as of 2019 the data is still being processed, and the images have yet to be released. The Event Horizon Telescope uses interferometry to combine images taken from widely spaced observatories at different places on Earth in order to gain a higher picture resolution. It is hoped the measurements will test Einstein's theory of relativity more rigorously than has previously been done. If discrepancies between the theory of relativity and actual observation are found, scientists may have identified physical circumstances under which the theory breaks down.[12] HistoryKarl Jansky, considered a father of radio astronomy, discovered in August 1931 that a radio signal was coming from a location at the center of the Milky Way, in the direction of the constellation of Sagittarius.[13] Sgr A* was discovered on February 13 and 15, 1974, by astronomers Bruce Balick and Robert Brown using the baseline interferometer of the National Radio Astronomy Observatory.[14][15] 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.[16][17]On October 16, 2002, an international team led by Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics reported the observation of the motion of the star S2 near Sagittarius A* over 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.[18] The observations of S2 used near-infra red (NIR) interferometry (in the K-band, i.e. 2.2 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 images so S2 could be seen to orbit Sagittarius A*. From examining the Keplerian orbit of S2, they determined the mass of Sagittarius A* to be 2.6 ± 0.2 million solar masses, confined in a volume with a radius no more than 17 light-hours (120 AU).[20] 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) or about 6.7 billion kilometres.[2] S175 passed within a similar distance.[21] For comparison, the Schwarzschild radius is 0.08 AU. 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 8.0 ± 0.6 × 103 parsecs. In November 2004 a team of astronomers reported the discovery of a potential intermediate-mass black hole, referred to as GCIRS 13E, orbiting three 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. estimate 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.[22] Reinhard Genzel, team leader of the research, said the study has delivered "what is now considered to be the best empirical evidence that super-massive 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."[23] 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.[24] {{Multiple image|direction=horizontal|align=center|width=300|image1=15-044a-SuperNovaRemnant-PlanetFormation-SOFIA-20150319.jpg|image2=15-044b-SuperNovaRemnant-PlanetFormation-SOFIA-20150319.jpg|footer=Central black hole{{update|inaccurate=y|date=November 2018|reason= Reasons are given in the talk page discussion}}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 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*.[25][26] In July 2018, it was reported that S2 orbiting Sgr A* had been recorded at 7,650km/s or 2.55% the speed of light leading up to the pericentre approach, in May 2018, at about 120 AU ≈ 1400 Schwarzschild radii from Sgr A*. At that close distance to the black hole, Einstein's Theory of General Relativity predicts that S2 would show a discernible gravitational redshift in addition to the usual velocity redshift; the gravitational redshift was detected, in agreement with GR prediction within the 10 percent measurement precision.[27][28] Assuming that general relativity is still a valid description of gravity near the event horizon then 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.[29] If the apparent position of Sagittarius A* were exactly centered on the black hole, it would be possible to see it magnified beyond its actual 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. 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 50μas.[29] Recent lower resolution observations revealed that the radio source of Sagittarius A * is symmetrical.[30] These results are at tension with General Relativity which if no other viable explanation is found within the general relativistic paradigm may demand a new theory of gravitation or modifications to General Relativity itself. [https://scitechdaily.com/astrophysicists-test-theories-of-gravity-with-black-hole-shadows/ Simulations of alternative theories of gravity] depict results indistinguishable from GR. However, a new [https://www.hindawi.com/journals/ahep/2018/4537058/ paper] predicts an image of Sagittarius A * that is in agreement with recent observations; in particular, it explains the small angular size and the [https://m.phys.org/news/2019-01-revealing-black-hole-heart-galaxy.html symmetrical morphology of the source]. The mass of Sagittarius A* has been estimated in two different ways:
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.[9] 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.[25] The black hole itself is thought to emit only Hawking radiation at a negligible temperature, on the order of 10−14 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 ({{math|L}}≈1,5{{e|39}} 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.[32][33] In 2011 this conclusion was supported by Japanese astronomers observing the Milky Way's center with the Suzaku satellite.[34] Orbiting stars
Discovery of G2 gas cloud on an accretion courseFirst noticed as something unusual in images of the center of the Milky Way in 2002,[39] 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.[40] 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 3000 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,[40] 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.[41] In addition to the tidal effects on the cloud itself, it was proposed in May 2013[42] 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 into the region surrounding the supermassive black hole at the center of the Milky Way.[43] The average rate of accretion onto Sgr A* is unusually small for a black hole of its mass[44] 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, EVLA, INTEGRAL, Swift, Fermi and requested at VLT and Keck.[45] Simulations of the passage were made before it happened by groups at ESO[46] and Lawrence Livermore National Laboratory (LLNL).[47] As the cloud approached the black hole, Dr. 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.[48] 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".[68] 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.[49] 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.[50][51] Professor 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.[41][52] Sgr A* is monitored on a daily basis by the X-ray telescope of the Swift satellite. {{multiple image| align = center | direction = horizontal | image1 = A simulation of how a gas cloud that has been observed approaching the supermassive black hole at the centre of the galaxy.jpg | width1 = 200 | alt1 = | caption1 = Artist impression of the accretion of gas cloud G2 onto Sgr A*. Credit: ESO.[53] | image2 = Simulation of gas cloud being ripped apart by the black hole at the centre of the Milky Way.ogv | width2 = 200 | alt2 = | caption2 = This simulation shows a gas cloud, discovered in 2011, as it passes close to the supermassive black hole at the center of the Milky Way. | image3 = The dusty cloud G2 passes the supermassive black hole at the centre of the Milky Way.webm | width3 = 200 | alt3 = | caption3 = This video sequence shows the motion of the dusty cloud G2 as it closes in on, and then passes, the supermassive black hole at the center of the Milky Way. }}{{Clear}} See also{{portal|Astronomy|Cosmology}}
Notes1. ^Reid and Brunthaler 2004 2. ^1 2 {{cite journal | author = Ghez, A. M. | display-authors=et al. | title = Measuring Distance and Properties of the Milky Way's Central Supermassive Black Hole with Stellar Orbits | journal = Astrophysical Journal | date = December 2008 | volume = 689 | issue = 2 | pages = 1044–1062 | arxiv=0808.2870 | bibcode = 2008ApJ...689.1044G | doi = 10.1086/592738}} 3. ^1 {{Cite journal|arxiv=1607.05726 |title=An Improved Distance and Mass Estimate for Sgr A* from a Multistar Orbit Analysis|journal=The Astrophysical Journal|volume=830|issue=1|pages=17|date=2016-07-19 |last1=Boehle|first1=A|last2=Ghez|first2=A. M|last3=Schödel|first3=R|last4=Meyer|first4=L|last5=Yelda|first5=S|last6=Albers|first6=S|last7=Martinez|first7=G. D|last8=Becklin|first8=E. E|last9=Do|first9=T|last10=Lu|first10=J. R|last11=Matthews|first11=K|last12=Morris|first12=M. R|last13=Sitarski|first13=B|last14=Witzel|first14=G|doi=10.3847/0004-637X/830/1/17|bibcode=2016ApJ...830...17B}} 4. ^{{Cite news|url=https://metro.co.uk/2018/10/31/scientists-find-proof-a-supermassive-black-hole-is-lurking-at-the-centre-of-the-milky-way-8092994/|title=Scientists find proof a black hole is lurking at the centre of our galaxy|date=2018-10-31|work=Metro|access-date=2018-10-31|language=en-GB}} 5. ^{{Cite news|url=https://www.middletownpress.com/technology/businessinsider/article/Supermassive-black-holes-gorge-themselves-on-a-7971243.php|title=A 'mind-boggling' telescope observation has revealed the point of no return for our galaxy's monster black hole|date=2018-10-31|work=The Middletown Press|access-date=2018-10-31}} 6. ^{{cite web |last1=Plait |first1=Phil |title=Astronomers see material orbiting a black hole *right* at the edge of forever |url=https://www.syfy.com/syfywire/astronomers-see-material-orbiting-a-black-hole-right-at-the-edge-of-forever |website=https://www.syfy.com/ |publisher=Syfy Wire |accessdate=12 November 2018 |archiveurl=https://web.archive.org/web/20181110143143/https://www.syfy.com/syfywire/astronomers-see-material-orbiting-a-black-hole-right-at-the-edge-of-forever |archivedate=10 November 2018 |language=English|date=2018-11-08 }} 7. ^{{cite news|url=http://www.timesonline.co.uk/tol/news/uk/science/article5316001.ece|title=Astronomers confirm black hole at the heart of the Milky Way|last=Henderson|first=Mark|date=December 9, 2008 |publisher= Times Online|accessdate=2009-05-17}} 8. ^{{cite web |title=Cloudlets swarm around our local supermassive black hole |url=https://www.eso.org/public/images/potw1843a/ |website=www.eso.org |accessdate=22 October 2018}} 9. ^1 Osterbrock and Ferland 2006, p. 390 10. ^{{cite journal |vauthors=Falcke H, Melia F, Agol E |title=Viewing the Shadow of the Black Hole at the Galactic Center |journal=Astrophysical Journal Letters |volume=528 |issue=1 |pages=L13–L16 |year=2000 |doi=10.1086/312423 |pmid=10587484|arxiv=astro-ph/9912263 |bibcode=2000ApJ...528L..13F }} 11. ^Backer and Sramek 1999, § 3 12. ^[https://news.nationalgeographic.com/2017/04/black-hole-event-horizon-telescope-pictures-genius-science/ "Astronomers May Finally Have the First Picture of a Black Hole"], 11 Apr 2017 National Geographic 13. ^{{cite web|url=http://www.armaghplanet.com/blog/karl-jansky-the-father-of-radio-astronomy.html |title=Karl Jansky: The Father of Radio Astronomy |accessdate=2015-10-21}} 14. ^{{cite journal|last1=Balick, B.; Brown, R. L.|title=Intense sub-arcsecond structure in the galactic center|journal=Astrophysical Journal|date=1 December 1974|volume=194|issue=1|pages=265–270|doi=10.1086/153242|bibcode=1974ApJ...194..265B}} 15. ^Melia 2007, p. 7 16. ^{{Cite journal|arxiv=astro-ph/0305074 |title=[astro-ph/0305074] The Discovery of Sgr A* |journal=Astronomische Nachrichten |volume=324 |issue=1 |pages=497 |date=2003-05-06 |last1=Goss |first1=W. M |last2=Brown |first2=Robert L |last3=Lo |first3=K. Y |doi=10.1002/asna.200385047 |bibcode=2003ANS...324..497G }} 17. ^"Precessing jets in Sagittarius A – Gas dynamics in the central parsec of the galaxy", R. L. Brown, Astrophysical Journal, Part 1, 262, Nov. 1, 1982, pp. 110–119, {{bibcode|1982ApJ...262..110B}}. 18. ^Schödel et al. 2002 19. ^{{cite web|title=Best View Yet of Dusty Cloud Passing Galactic Centre Black Hole|url=http://www.eso.org/public/news/eso1512/|accessdate=16 June 2015}} 20. ^Ghez et al. 2003 21. ^{{Cite journal|last=Gillessen|first=S.|last2=Plewa|first2=P. M.|last3=Eisenhauer|first3=F.|last4=Sari|first4=R.|last5=Waisberg|first5=I.|last6=Habibi|first6=M.|last7=Pfuhl|first7=O.|last8=George|first8=E.|last9=Dexter|first9=J.|date=2017|title=An Update on Monitoring Stellar Orbits in the Galactic Center|url=http://stacks.iop.org/0004-637X/837/i=1/a=30|journal=The Astrophysical Journal|language=en|volume=837|issue=1|pages=30|doi=10.3847/1538-4357/aa5c41|issn=0004-637X|arxiv=1611.09144|bibcode=2017ApJ...837...30G}} 22. ^1 2 Gillessen et al. 2009 23. ^O'Neill 2008 24. ^1 {{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 |work=NASA |accessdate=January 6, 2015 }} 25. ^1 {{cite journal |doi=10.1051/0004-6361/201834294|title=Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA|journal=Astronomy & Astrophysics|volume=618|pages=L10|year=2018|last1=Abuter|first1=R.|last2=Amorim|first2=A.|last3=Bauböck|first3=M.|last4=Berger|first4=J. P.|last5=Bonnet|first5=H.|last6=Brandner|first6=W.|last7=Clénet|first7=Y.|last8=Coudé Du Foresto|first8=V.|last9=De Zeeuw|first9=P. T.|last10=Deen|first10=C.|last11=Dexter|first11=J.|last12=Duvert|first12=G.|last13=Eckart|first13=A.|last14=Eisenhauer|first14=F.|last15=Förster Schreiber|first15=N. M.|last16=Garcia|first16=P.|last17=Gao|first17=F.|last18=Gendron|first18=E.|last19=Genzel|first19=R.|last20=Gillessen|first20=S.|last21=Guajardo|first21=P.|last22=Habibi|first22=M.|last23=Haubois|first23=X.|last24=Henning|first24=Th.|last25=Hippler|first25=S.|last26=Horrobin|first26=M.|last27=Huber|first27=A.|last28=Jiménez-Rosales|first28=A.|last29=Jocou|first29=L.|last30=Kervella|first30=P.|displayauthors=29|bibcode=2018A&A...618L..10G|arxiv=1810.12641}} 26. ^{{cite web |title=Most Detailed Observations of Material Orbiting close to a Black Hole |url=https://www.eso.org/public/news/eso1835/ |website=European Southern Observatory (ESO) |accessdate=1 November 2018}} 27. ^[https://www.aanda.org/articles/aa/full_html/2018/07/aa33718-18/aa33718-18.html Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole], Genzel et al, Astronomy & Astrophysics, DOI 10.1051/0004-6361/201833718, 2018-07-26 28. ^[https://www.theguardian.com/science/2018/jul/26/star-spotted-speeding-near-milky-way-black-hole-for-first-time Star spotted speeding near black hole at centre of Milky Way -- Chile’s Very Large Telescope tracks S2 star as it reaches mind-boggling speeds by supermassive black hole], The Guardian, 2017-07-26 29. ^1 2 R. Lu et al. 2018. “Detection of intrinsic source structure at ~3 Schwarzschild radii with Millimeter-VLBI observations of Sgr A*.” ApJ, 859, 1, Pp. 60. 30. ^{{cite journal |last1=Issaoun |first1=S. |title=The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA |journal=The Astrophysical Journal |volume=871 |pages=30 |doi=10.3847/1538-4357/aaf732 |date=January 18, 2019|arxiv=1901.06226 }} 31. ^Schödel et al. 2009 32. ^{{cite news | date=January 28, 2005 | title=Integral rolls back history of Milky Way's super-massive black hole | publisher=Hubble News Desk | url=http://www.esa.int/SPECIALS/Integral/SEMSKPO3E4E_0.html | accessdate=2007-10-31 }} 33. ^{{cite journal | author=M. G. Revnivtsev | display-authors=et al. | title=Hard X-ray view of the past activity of Sgr A* in a natural Compton mirror | journal=Astronomy and Astrophysics | date=2004 | volume=425 | issue=3 | pages=L49–L52 | bibcode=2004A&A...425L..49R | doi=10.1051/0004-6361:200400064| arxiv=astro-ph/0408190}} 34. ^{{cite journal | author=M. Nobukawa | display-authors=et al. | title=New Evidence for High Activity of the Supermassive Black Hole in our Galaxy | journal=The Astrophysical Journal Letters | date=2011 | volume=739 | issue=2 | pages=L52 | bibcode=2011ApJ...739L..52N | doi=10.1088/2041-8205/739/2/L52| arxiv=1109.1950}} 35. ^1 2 3 4 5 6 {{cite journal|last=Eisenhauer|first=F.|display-authors=et al. |title=SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month|journal=The Astrophysical Journal|date=July 20, 2005|volume=628|issue=1|pages=246–259| url=http://iopscience.iop.org/0004-637X/628/1/246/62163.text.html|doi=10.1086/430667|bibcode=2005ApJ...628..246E|arxiv=astro-ph/0502129}} 36. ^{{cite journal| url=http://www.astrophysicsspectator.com/tables/MilkyWayCentralStars.html| title=Orbital Parameters of Stars Orbiting Sgr A*| issue= 4.10| date= July 11, 2007| journal= The Astrophysics Spectator}} 37. ^1 2 {{cite journal |last=Ghez |first=A. M. |authorlink=Andrea Ghez |author2=Salim, S. |author3=Hornstein, S. D. |author4=Tanner, A. |author5=Lu, J. R. |author6=Morris, M. |author7=Becklin, E. E. |author8= Duchêne, 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 }} 38. ^{{Cite journal |title=The Shortest Known Period Star Orbiting our Galaxy's Supermassive Black Hole |last=Meyer |first=L. |author2=Ghez, A. M. |author3=Schödel, R. |author4=Yelda, S. |author5=Boehle, A. |author6=Lu, J. R. |author7=Do, T. |author8=Morris, M. R. |author9=Becklin, E. E. |author10=Matthews, K. |date=4 October 2012 |arxiv=1210.1294 |doi=10.1126/science.1225506 |pmid=23042888 |volume=338 |issue=6103 |journal=Science |pages=84–87|bibcode=2012Sci...338...84M }} 39. ^{{cite web|last=Matson|first=John|title=Gas Guzzler: Cloud Could Soon Meet Its Demise in Milky Way's Black Hole|url=https://www.llnl.gov/news/newsreleases/2012/Oct/NR-12-10-07.html|publisher=Scientific American|accessdate=2012-10-30|date=2012-10-22}} 40. ^1 {{cite journal|last=Gillessen|first=S.|author2=Genzel|author3=Fritz|author4=Quataert|author5=Alig|author6=Burkert|author7=Cuadra|author8=Eisenhauer|author9=Pfuhl|author10=Dodds-Eden|author11=Gammie|author12=Ott|title=A gas cloud on its way towards the supermassive black hole at the Galactic Centre|journal=Nature|date=5 January 2012|volume=481|issue=7379|pages=51–54|doi=10.1038/nature10652|pmid=22170607|arxiv=1112.3264|bibcode=2012Natur.481...51G}} 41. ^1 {{cite journal|url=http://stacks.iop.org/2041-8205/796/i=1/a=L8|title=Detection of Galactic Center Source G2 at 3.8 μm during Periapse Passage|first1=G.|last1=Witzel|first2=A. M.|last2=Ghez|first3=M. R.|last3=Morris|first4=B. N.|last4=Sitarski|first5=A.|last5=Boehle|first6=S.|last6=Naoz|first7=R.|last7=Campbell|first8=E. E.|last8=Becklin|last9=G. Canalizo|first10=S.|last10=Chappell|first11=T.|last11=Do|first12=J. R.|last12=Lu|first13=K.|last13=Matthews|first14=L.|last14=Meyer|first15=A.|last15=Stockton|first16=P.|last16=Wizinowich|first17=S.|last17=Yelda|date=1 January 2014|journal=Astrophysical Journal Letters|volume=796|issue=1|pages=L8|via=Institute of Physics|doi=10.1088/2041-8205/796/1/L8|arxiv=1410.1884|bibcode=2014ApJ...796L...8W}} 42. ^{{cite journal |last1=Bartos|first1=Imre|last2=Haiman|first2=Zoltán|last3=Kocsis|first3=Bence|last4=Márka|first4=Szabolcs|title=Gas Cloud G2 Can Illuminate the Black Hole Population Near the Galactic Center|journal=Physical Review Letters |date=May 2013 |volume=110|issue=22|pages=221102 (5 pages)|doi=10.1103/PhysRevLett.110.221102|arxiv=1302.3220|bibcode=2013PhRvL.110v1102B|pmid=23767710}} 43. ^{{cite journal |last1=de la Fuente Marcos|first1=R.|last2=de la Fuente Marcos|first2=C.|title=Colliding with G2 near the Galactic Centre: a geometrical approach|journal=Letters|date=August 2013 |volume=435|issue=1|pages=L19–L23|doi=10.1093/mnrasl/slt085|url=http://mnrasl.oxfordjournals.org/content/435/1/L19|arxiv=1306.4921|bibcode=2013MNRAS.435L..19D }} 44. ^{{cite journal|last=Morris|first=Mark|title=Astrophysics: The Final Plunge|journal=Nature|date=4 January 2012|volume=481|issue=7379|pages=32–33|doi=10.1038/nature10767|pmid=22170611|bibcode=2012Natur.481...32M}} 45. ^{{cite web|last=Gillessen|title=Wiki Page of Proposed Observations of G2 Passage|url=https://wiki.mpe.mpg.de/gascloud/ProposalList|accessdate=30 October 2012}} 46. ^{{cite web|url=http://www.eso.org/public/news/eso1151/ |title=A Black Hole's Dinner is Fast Approaching |publisher=ESO |date=2011-12-14 |accessdate=2015-02-27}} 47. ^{{cite web|author=Robert H Hirschfeld |url=https://www.llnl.gov/news/newsreleases/2012/Oct/NR-12-10-07.html |title=Milky Way's black hole getting ready for snack |publisher=[www.Llnl.gov Lawrence Livermore National Laboratory] |date=2012-10-22 |accessdate=2015-02-27}} 48. ^space.com, Doomed Space Cloud Nears Milky Way's Black Hole as Scientists Watch, 28 April 2014 "Cosmic encounter that might reveal new secrets on how such supermassive black holes evolve"; "We get to watch it unfolding in a human lifetime, which is very unusual and very exciting" 49. ^{{cite journal|author1= A. M. Ghez |author2=G . Witzel |author3= B. Sitarski |author4= L. Meyer |author5=S. Yelda |author6= A. Boehle |author7=E. E. Becklin |author8= R. Campbell |author9= G. Canalizo |author10= T. Do |author11= J. R. Lu |author12= K. Matthews |author13= M. R. Morris |author14= A. Stockton | title =Detection of Galactic Center Source G2 at 3.8 micron during Periapse Passage Around the Central Black Hole | journal =The Astronomer's Telegram | issue =6110 | date =2 May 2014 | url =http://www.astronomerstelegram.org/?read=6110 | accessdate = May 3, 2014}} 50. ^1 {{Cite journal|url=http://www.nature.com/news/why-galactic-black-hole-fireworks-were-a-flop-1.15591 |title=Why galactic black hole fireworks were a flop : Nature News & Comment |journal=Nature |accessdate=2015-02-27|doi=10.1038/nature.2014.15591 |year=2014 |last1=Cowen |first1=Ron }} 51. ^{{Cite journal|last=Pfuhl|first=Oliver|last2=Gillessen|first2=Stefan|last3=Eisenhauer|first3=Frank|last4=Genzel|first4=Reinhard|last5=Plewa|first5=Philipp M.|last6=Thomas Ott|last7=Ballone|first7=Alessandro|last8=Schartmann|first8=Marc|last9=Burkert|first9=Andreas|date=2015|title=The Galactic Center Cloud G2 and its Gas Streamer|url=http://stacks.iop.org/0004-637X/798/i=2/a=111|journal=The Astrophysical Journal|language=en|volume=798|issue=2|pages=111|doi=10.1088/0004-637x/798/2/111|issn=0004-637X|arxiv=1407.4354|bibcode=2015ApJ...798..111P}} 52. ^{{cite web|url=http://earthsky.org/space/how-g2-survived-the-black-hole-at-our-milky-ways-heart|title=How G2 survived the black hole at our Milky Way's heart - EarthSky.org}} 53. ^{{cite web|url=http://www.eso.org/public/images/eso1151a/ |title=Simulation of gas cloud after close approach to the black hole at the centre of the Milky Way |publisher=ESO |date= |accessdate=2015-02-27}} References{{Div col|colwidth=30em}}
External links{{Commons category|Sagittarius A}}
6 : Astronomical objects discovered in 1974|Astronomical radio sources|Milky Way|Supermassive black holes|Sagittarius (constellation)|Articles containing video clips |
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