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 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. 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 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
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when com ...
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 around the orbits of these stars.]
References
External links
*
* Includes position measurements and images.
{{DEFAULTSORT:S0-102
Sagittarius (constellation)