S55 (also known as S0–102) is a star that is located very close to the centre of the Milky Way, near the radio source
Sagittarius A*, orbiting it with an orbital period of 12.8 years. Until 2019, when the star
S62 became the new record holder, it was the star with the shortest known period orbiting the black hole at the centre of the Milky Way. This beat the record of 16 years previously set by
S2. The star was identified by a
University of California, Los Angeles
The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California St ...
team headed by
Andrea M. Ghez
Andrea Mia Ghez (born June 16, 1965) is an American astrophysicist and professor in the Department of Physics and Astronomy and the Lauren B. Leichtman & Arthur E. Levine chair in Astrophysics, at the University of California, Los Angeles. Her ...
. At its
periapsis, its speed reaches 1.7% of the
speed of light
The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
. At that point it is 246
astronomical units (34 light hours, 36.7 billion km) from the centre,
while the black hole radius is only a small fraction of that size (the
Schwarzschild radius
The Schwarzschild radius or the gravitational radius is a physical parameter in the Schwarzschild solution to Einstein's field equations that corresponds to the radius defining the event horizon of a Schwarzschild black hole. It is a characteristic ...
is about ).
It passed that point in 2009 and will be there again in 2022.
Its position in the sky has been monitored from 2000 to 2012 using the
W. M. Keck telescope and from 2002 to 2016 with the
VLT. One complete orbit has been observed. From Earth's current perspective, it travels in a clockwise direction. Having observed two stars orbiting through complete periods around the centre (S55 and S2), the
gravitational potential of SgrA* could be established.
[ It is also possible that there is a great deal of ]dark matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...
around the orbits of these stars.
References
External links
*
* Includes position measurements and images.
{{DEFAULTSORT:S0-102
Sagittarius (constellation)