| caption = S2 and Sgr A }} -->
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 hours. Given a recent estimate of 3.7 million Msun for the mass of Sagittarius A*, the maximum gravitational acceleration experienced by S2 at the pericenter of its orbit would be about 1.5 m/s2 or almost one-sixth of Earth's surface gravity.
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 black hole. A large part of one orbit had been observed as of 2004.
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.
The 'S' in 'S2' simply stands for 'star'.
|NAME||Right ascension||Declination||Apparent magnitude (V)||Spectral type||Database references|
|Sgr A*||17h 45m 12s||-28° 48' 18''||radio source||Simbad|