S2 (star)
 The clock-wise orbit of 'S2' around Sagittarius A* |
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 17h 45m 40.044s[1] |
| Declination | −29° 00′ 28″[1] |
| Characteristics | |
| Spectral type | "B1V[1] |
| Variable type | None |
| Astrometry | |
| Distance | 25900 ± 1400 ly (7940 ± 420[2] pc) |
| Orbit[2] | |
| Companion | Sagittarius A* |
| Period (P) | 15.56 ± 0.35 yr |
| Semimajor axis (a) | 0.1203 ± 0.0027" |
| Eccentricity (e) | 0.881 ± 0.007 |
| Inclination (i) | −48.1 ± 1.3° |
| Longitude of the node (Ω) | 45.0 ± 1.6° |
| Periastron epoch (T) | 2002.331 ± 0.012 |
| Argument of periastron (ω) (secondary) |
245.4 ± 1.7° |
| Other designations | |
|
[CRG2004] 13, [GKM98] S0-2, [PGM2006] E1, [EG97] S2, [GPE2000] 0.15, [SOG2003] 1, S0—2.
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| Database references | |
| SIMBAD | data |
S2, also known as S0—2 (the 'S' in 'S2' stands for 'source'), 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 hours (18 Tm or 120 AU) — about 4 times the distance of Neptune from the Sun.
Its changing apparent position has been monitored since 1995 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, it has been observed to have completed one orbit. [3]
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 kiloparsecs, in close agreement with prior determinations of the distance by other methods.[2][4]
The orbit of S2 will give astronomers an opportunity to test for various effects predicted by general relativity and even extra-dimensional effects.[5] Given a recent estimate of 3.7 million solar masses 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 2% of the speed of light and acceleration of about 1.5 m/s2 or almost one-sixth of Earth's surface gravity.[6]
[edit] Component
| NAME | Right ascension | Declination | Apparent magnitude (V) | Spectral type | Database references |
|---|---|---|---|---|---|
| Sgr A* | 17h 45m 12s | -28° 48' 18 | radio source | Simbad |
[edit] External links
- "Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours", ESO Press Release, October 16, 2002
- S2 page on the SIMBAD database
[edit] References
- ^ a b c [PGM2006] E1 -- Star in double system, database entry, SIMBAD. Accessed on line July 15, 2008.
- ^ 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.
- ^ A short documentary on Sagittarius A*
- ^ Max-Planck-Institut für extraterrestrische Physik—Infrared/Submillimeter Astronomy—Galactic Center Research
- ^ Black Hole as Peephole
- ^ Surfing a Black Hole
- ^ "SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month" by Eisenhauer et al, The Astrophysical Journal, 628:246-259, 2005
