S2 (star)
Encyclopedia
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.
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 orbit of S2 will give astronomers an opportunity to test for various effects predicted by general relativity
and even extra-dimensional effects. Given a recent estimate of 3.7 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 2% of the speed of light and acceleration of about 1.5 m/s2 or almost one-sixth of Earth's surface gravity.
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
) — about 4 times the distance of Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
.
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
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
in the center of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
. 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.
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 orbit of S2 will give astronomers an opportunity to test for various effects predicted by general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
and even extra-dimensional effects. Given a recent estimate of 3.7 million solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
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 2% of the speed of light and acceleration of about 1.5 m/s2 or almost one-sixth of Earth's surface gravity.
External links
- "Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours", ESOESOESO, as a three-letter abbreviation, may stand for:* European Southern Observatory* Ensemble Studios Online* English Symphony Orchestra* Edmonton Symphony Orchestra* Executive Stock Options...
Press Release, October 16, 2002 - http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%5BEG97%5D+S2S2 page on the SIMBADSIMBADSIMBAD is an astronomical database of objects beyond the Solar System...
database]
Component
| NAME | Right ascension Right ascension Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:... |
Declination Declination In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and... |
Apparent magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere... (V) |
Spectral type | Database references |
|---|---|---|---|---|---|
| Sgr A* | 17h 45m 12s | -28° 48' 18 | radio source | Simbad |