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| {{Starbox begin
| | Let me inroduce myself, my name is Brendan but it's not the most masculine company name. What he loves doing would play pebble but he's thinking on [http://www.encyclopedia.com/searchresults.aspx?q=starting+today%27s starting today's] truck owner. She currently lives in The state of washington. Meter reading is buying and selling domains make cash and it is something I actually enjoy. Go to his site find out more: http://www.ecreator.org/ugg/[https://www.flickr.com/search/?q=comprar-ugg-online.html comprar-ugg-online.html]<br><br>Here is my web-site [http://www.ecreator.org/ugg/comprar-ugg-online.html Comprar Ugg Online] |
| | name = S 2
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| }}
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| {{Starbox image
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| | image = [[File:Orbit of S2.jpg|175px]]
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| | caption = The clock-wise orbit of 'S2' around Sagittarius A*
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| }}
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| {{Starbox observe
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| | epoch = [[J2000.0]] ([[International Celestial Reference System|ICRS]])
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| | ra={{RA|17|45|40.044}}<ref name="sb">{{SIMBAD link|%5BEG97%5D+S2|[PGM2006] E1 -- Star in double system}}, database entry, [[SIMBAD]]. Accessed on line July 15, 2008.</ref>
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| | dec = {{DEC|−29|00|28}}<ref name="sb" />
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| | constell = [[Sagittarius (constellation)|Sagittarius]]
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| }}
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| {{Starbox character
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| | class="B1V<ref name="sb" />
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| | variable = None
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| }}
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| {{Starbox astrometry
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| | dist_pc = 7940 ± 420<ref name="geom"/>
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| | dist_ly = 25900 ± 1400
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| }}
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| {{Starbox visbin
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| |reference=<ref name="geom">
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| {{cite journal
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| | author = Eisenhauer, F. et al.
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| | year = 2003
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| | title = A Geometric Determination of the Distance to the Galactic Center
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| | journal = The Astrophysical Journal
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| | volume = 597 | issue = 2 | pages = L121–L124
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| | doi = 10.1086/380188
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| | bibcode = 2003ApJ...597L.121E
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| | arxiv = astro-ph/0306220
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| }}</ref>
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| | name=Sagittarius A*
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| | period=15.56 ± 0.35
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| | axis=0.1203 ± 0.0027
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| | eccentricity=0.881 ± 0.007
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| | inclination=−48.1 ± 1.3
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| | node=45.0 ± 1.6
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| | periastron=2002.331 ± 0.012
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| | periarg = 245.4 ± 1.7
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| }}
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| {{Starbox catalog
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| | names = [CRG2004] 13, [GKM98] S0-2, [PGM2006] E1, [EG97] S2, [GPE2000] 0.15, [SOG2003] 1, S0—2.
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| }}
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| {{Starbox reference
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| | Simbad=%5BEG97%5D+S2
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| }}
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| {{Starbox end}}
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| '''Source 2'''<!--is it hyphenated?--> (abbreviated '''S2'''), also known as '''S0—2''', is a star that is located close to the radio source [[Sagittarius A*]], orbiting it with an orbital period of 15.56 ± 0.35 years and a [[pericenter]] distance of 17 [[Light-hour|light hours]] (18 [[Metre#SI prefixed forms of metre|Tm]] or 120 [[astronomical unit|AU]]) — about four times the distance of [[Neptune]] from the [[Sun]]. As of 2002, its mass was estimated by the European Southern Observatory (ESO) to be approximately <math>15 M_\odot</math>.<ref>European Southern Observatory (ESO) public data on S2 and Central Black Hole"[http://www.solstation.com/x-objects/s2.htm]"</ref>
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| Its changing apparent position has been monitored since 1995 by two groups (at [[UCLA]] and at the [[Max Planck Institute for Extraterrestrial Physics]]) as part of an effort to gather evidence for the existence of a [[supermassive black hole]] in the center of the [[Milky Way]] [[galaxy]]. The accumulating evidence points to Sagittarius A* as being the site of such a black hole. {{As of|2008}}, S2 has been observed for one complete orbit.<ref>{{YouTube|KCADH3x56eE|A short documentary on Sagittarius A*}}</ref>
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| A team of astronomers mainly from the Max Planck Institute for Extraterrestrial Physics used observations of S2's orbital dynamics around Sgr A* to measure the distance from the Earth to the galactic center. They determined the distance to be 7.94 ± 0.42 [[kiloparsec]]s, in close agreement with prior determinations of the distance by other methods.<ref name="geom"/><ref>[http://www2011.mpe.mpg.de/ir/GC/papers/nature2002.pdf Max-Planck-Institut für extraterrestrische Physik—Infrared/Submillimeter Astronomy—Galactic Center Research]</ref>
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| The orbit of S2 will give astronomers an opportunity to test for various effects predicted by [[general relativity]] and even extra-dimensional effects.<ref>[http://www.sciencenews.org/view/generic/id/56380/title/Black_hole_as_a_peephole Black Hole as Peephole]</ref> Given a recent estimate of 4.3 million [[solar mass]]es for the mass of Sagittarius A* and S2's close approach, this makes S2 the fastest known ballistic orbit, reaching speeds exceeding 5000 km/s (11,000,000 mph) or 1.67~% of the speed of light and acceleration of about 1.5 m/s<sup>2</sup> or almost one-sixth of Earth's surface gravity.<ref>[http://www.eso.org/public/news/eso0226/ Surfing a Black Hole]</ref> | |
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| The motion of S2 is also useful for detecting the presence of other objects near to Sagittarius A*. It is believed that there are thousands of stars, as well as dark stellar remnants (stellar black holes, [[neutron star]]s, [[white dwarf]]s) distributed in the volume through which S2 moves. These objects will perturb S2's orbit, causing it to deviate gradually from the [[Kepler orbit|Keplerian ellipse]] that characterizes motion around a single [[Point particle#Point mass|point mass]].<ref>{{cite journal |journal=Astronomy and Astrophysics |title=The S-Star Cluster at the Center of the Milky Way: On the nature of diffuse NIR emission in the inner tenth of a parsec |first=Nadeen |last=Sabha |first2=Andreas |last2=Eckart | first3=David | last3=Merritt | authorlink3=David Merritt|coauthors=Mohammad Zamaninasab, Gunther Witzel, Macarena García-Marín, Behrang Jalali, Monica Valencia-S., Senol Yazici, Rainer Buchholz, Banafsheh Shahzamanian, Christian Straubmeier |volume = 545 | pages = A70 | date=September 2012 }}</ref> So far, the strongest constraint that can be placed on this mass is that it comprises less than one percent of the mass of the supermassive black hole.<ref>
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| {{cite journal |last1= Gillessen|first1=S. |coauthors=et al. |year=2009 |title=Monitoring Stellar Orbits Around the Massive Black Hole in the Galactic Center |journal=The Astrophysical Journal |volume=692 |issue=2 |pages= 1075–1109 |publisher= IOP Publishing|doi=10.1088/0004-637X/692/2/1075 |url= http://adsabs.harvard.edu/abs/2009ApJ...692.1075G|accessdate= |bibcode = 2009ApJ...692.1075G |arxiv = 0810.4674 }}</ref>
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| [[Image:Galactic centre orbits.svg|thumb|300px|none|Inferred orbits of S2 and 5 other stars around supermassive black hole candidate Sagittarius A* at the Milky Way galactic centre.<ref>{{cite doi|10.1086/430667}}</ref>]]
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| In 2012, a star called [[S0-102]] was found to be orbiting even closer to the Milky Way's central supermassive black hole than does SO-2. At one-sixteenth the brightness of S0-2, S0-102 was not initially recognized because it required many more years of observations to distinguish it from its local infrared background. S0-102 has an orbital period of 11.5 years, even shorter than that of S0-2. Of all the stars orbiting the black hole, only these two have their orbital parameters and trajectories fully known in all three dimensions of space. The discovery of two stars orbiting the central black hole so closely with their orbits fully described is of extreme interest to astronomers, as the pair together will allow much more precise measurements on the nature of gravity and general relativity around the black hole than would be possible from using S0-2 alone.
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| [[Image:SO-102 Orbital Plot.jpg|thumb|none|Orbits of S0-2 and S0-102 around the Milky Way galaxy's supermassive black hole.]]
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| ==Component==
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| {| border="0" width="100%" cellpadding="2" cellspacing="1" style="float:right; margin-right:0.5em; background:#CDC9C9;"
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| ! colspan="1" | NAME || [[Right ascension]] || [[Declination]] || [[Apparent magnitude]] (V) || [[Spectral type]] || Database references
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| |- bgcolor="#FFFAFA"
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| | [[Sagittarius A*|Sgr A*]] || 17<sup>h</sup> 45<sup>m</sup> 12<sup>s</sup> || -28° 48' 18'' || || [[astronomical radio source|radio source]] || [http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=Sagittarius+A&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id Simbad]
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| |}
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| {{clear}}
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| ==References==
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| {{reflist}}
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| ==External links==
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| *[http://www.eso.org/public/news/eso0226/ "Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours"], [[ESO]] Press Release, October 16, 2002
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| *{{YouTube|uVlcIb-rClI|Stars Orbiting around the Black Hole at the Center of the Milky Way}}
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| *[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%5BEG97%5D+S2 S2 page on the [[SIMBAD]] database]
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| {{Stars of Sagittarius}}
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| {{DEFAULTSORT:S2 (Star)}}
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| [[Category:B-type main-sequence stars]]
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| [[Category:Sagittarius (constellation)]]
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| [[Category:Radio stars (astronomy)]]
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| [[Category:Objects within 100 kly of Earth]]
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