Testing General Relativity
According to Newton's theory, stellar orbits around the black hole follow elliptical paths. However, Einstein's relativity theory predicts that their orbits advance by a very small amount, tracing altered pattern as shown in the drawing. The difference between the two orbits is most prominent when the stars are at their closest approach with the central black hole.
After two decades of monitoring the orbital motions of stars in the Galaxy's central potential, the Galactic Center Group stands on the precipice of being able to carry out measurements that offer the unique opportunity to test the General Relativity description of gravity, the least tested of the four fundamental forces forces of nature in an unexplored regime. Future measurements of the short-period stars afford the opportunity to probe the structure of space time in a gravitational potential that is 100 times stronger and on a mass scale that is 400,000 times larger than any other existing test, providing tests of GR that many theorists have long anticipated.
The star S0-2 has a highly eccentric 15-year orbit and it will reach its closest approach in 2018, bringing it within 100 AU of the Galactic black hole. This corresponds to about 1000 times the black hole's event horizon (or Schwarzschild radius). During the pericenter passage, the difference between a Newtonian description of the S0-2's orbit and a relativistic one will be significantly larger than the measurement errors, offering an opportunity to test Einstein's Generay Relativity theory in an unexplored regime.