Is S0-2 a Binary Star?
http://aasnova.org/2017/10/17/is-s0-2-a-binary-star/
The most exciting discoveries in astronomy all have something in common: they let us marvel at the fact that nature obeys laws of physics.
The star S0-2 is one of these exciting discoveries. S0-2 (also known as S2) is a fast-moving star that has been observed to follow a full
elliptical, 16-year orbit around the Milky Way’s central supermassive black hole, precisely according to Kepler’s laws of planetary motion.
Serving as a test-particle probe of the gravitational potential, S0-2 provides some of the best constraints on the black hole’s mass and
distance yet. S0-2 is the brightest of the S-stars, a group of young main-sequence stars concentrated within the inner 1” (0.13 ly) of
the nuclear star cluster.
The next time S0-2 reaches its closest approach to the black hole, in 2018, there will exist a unique opportunity to detect a deviation from
Keplerian motion — namely the relativistic redshift of S0-2’s radial (line-of-sight) velocity — in a direct measurement. In anticipation of
this event, the authors of today’s paper investigate possible consequences of S0-2 being not a single star, but a spectroscopic binary, which
would complicate this measurement.