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S2 (star)

S2

Image of the Galactic Center showing the position of S2
Credit: ESO / MPE / Gillessen et al.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 17h 45m 40.0442s[1]
Declination −29° 00′ 27.975″[1]
Characteristics
Spectral type B0-2 V[2]
Astrometry
Distance7,940±420[3] pc
Orbit[3]
CompanionSagittarius A*
Period (P)16.0518[4] yr
Semi-major axis (a)0.12540 ± 0.00018″
Eccentricity (e)0.88466 ± 0.00018
Inclination (i)133.818 ± 0.093°
Longitude of the node (Ω)227.85 ± 0.19°
Periastron epoch (T)2018.37974 ± 0.00015
Argument of periastron (ω)
(secondary)		66.13 ± 0.12°
Other designations
[CRG2004] 13, [GKM98] S0–2, [PGM2006] E1, [EG97] S2, [GPE2000] 0.15, [SOG2003] 1, S0–2.
Database references
SIMBADdata

S2, also known as S0–2, is a star in the star cluster close to the supermassive black hole Sagittarius A* (Sgr A*), orbiting it with a period of 16.0518 years, a semi-major axis of about 970 au, and a pericenter distance of 17 light hours (18 Tm or 120 au) – an orbit with a period only about 30% longer than that of Jupiter around the Sun, but coming no closer than about four times the distance of Neptune from the Sun. The mass when the star first formed is estimated by the European Southern Observatory (ESO) to have been approximately 14 M☉.[5] Based on its spectral type (B0V ~ B3V), it probably has a mass of 10 to 15 solar masses.[citation needed]

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 Sgr A* as being the site of such a black hole. By 2008, S2 had been observed for one complete orbit.[6] In 2020, partway through its next orbit, the GRAVITY collaboration released an analysis showing full agreement with Schwarzschild geodesics.[7]

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 it to be 7.94 ± 0.42 kiloparsecs, in close agreement with prior determinations by other methods.[3][8]

S2 was precisely tracked during its May 2018 close approach to Sgr A*, with results in accord with general relativity predictions.[9]

  1. ^ a b Schödel, R.; Merritt, D.; Eckart, A. (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. S2CID 219559.
  2. ^ Paumard, T.; Genzel, R.; Martins, F.; Nayakshin, S.; Beloborodov, A.M.; Levin, Y.; Trippe, S.; Eisenhauer, F.; Ott, T.; Gillessen, S.; Abuter, R.; Cuadra, J.; Alexander, T.; Sternberg, A. (2006). "The two young star disks in the central parsec of the galaxy: Properties, dynamics, and formation". The Astrophysical Journal. 643 (2): 1011–1035. arXiv:astro-ph/0601268. Bibcode:2006ApJ...643.1011P. doi:10.1086/503273. S2CID 14440768.
  3. ^ a b c Eisenhauer, F.; et al. (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. S2CID 16425333.
  4. ^ Hees, A. (2017). "Testing General Relativity with stellar orbits around the supermassive black hole in our galactic center". Physical Review Letters. 118 (21): 211101. arXiv:1705.07902. Bibcode:2017PhRvL.118u1101H. doi:10.1103/PhysRevLett.118.211101. PMID 28598651. S2CID 206291276.
  5. ^ Habibi, M.; et al. (2017). "Twelve years of spectroscopic Monitoring in the galactic center: The closest look at S-stars near the black hole". The Astrophysical Journal. 847 (2): 120. arXiv:1708.06353. Bibcode:2017ApJ...847..120H. doi:10.3847/1538-4357/aa876f. S2CID 119078556.
  6. ^ A short documentary on Sagittarius A* on YouTube
  7. ^ Abuter, R.; Amorim, A.; Bauböck, M.; Berger, J. P.; Bonnet, H.; Brandner, W.; Cardoso, V.; Clénet, Y.; De Zeeuw, P. T.; Dexter, J.; Eckart, A.; Eisenhauer, F.; Förster Schreiber, N. M.; Garcia, P.; Gao, F.; Gendron, E.; Genzel, R.; Gillessen, S.; Habibi, M.; Haubois, X.; Henning, T.; Hippler, S.; Horrobin, M.; Jiménez-Rosales, A.; Jochum, L.; Jocou, L.; Kaufer, A.; Kervella, P.; Lacour, S.; et al. (GRAVITY Collaboration) (16 April 2020). "Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole". Astronomy & Astrophysics. 636 (L5): L5. arXiv:2004.07187. Bibcode:2020A&A...636L...5G. doi:10.1051/0004-6361/202037813. S2CID 215768928.
  8. ^ "Galactic Center Research" (PDF). Infrared/Submillimeter Astronomy. Max-Planck-Institut für extraterrestrische Physik. Archived from the original (PDF) on 2006-09-06. Retrieved 2013-03-26.
  9. ^ Do, Tuan; et al. (16 Aug 2019). "Relativistic redshift of the star S0–2 orbiting the Galactic center supermassive black hole". Science. 365 (6454): 664–668. arXiv:1907.10731. Bibcode:2019Sci...365..664D. doi:10.1126/science.aav8137. PMID 31346138. S2CID 198901506.

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