In the heart of the Milky Way galaxy is a supermassive black hole with about 4 million times the mass of our Sun. Data gathered over the past 17 years (between 1995 and 2012) by the Keck Observatory in Hawaii has revealed the presence of a star with the shortest known orbital period around the supermassive black hole. To compensate for the distorting effects of the Earth’s atmosphere, a combination of speckle imaging (1995 to 2005) and adaptive optics (2004 to 2012) observations were used. Named S0-102, this star orbits the supermassive black hole with a period of just 11.5 years. The previous record holder was S0-2 which has an orbital period of 16 years.
The gravitational potential in this region of the galaxy is dominated by the supermassive black hole and effects arising from the curvature of space time due to the strong gravitational field are expected. Deviations in the orbits of S0-102 and S0-2 from pure Keplerian orbits are likely to be detected in future. These 2 stars will be useful for testing Einstein’s General Theory of Relativity. Furthermore, the wavelength of light being emitted by S0-102 and S0-2 is expected to be gravitationally redshifted to a detectable amount. The gravitational redshift will be largest when the star is at closest approach to the supermassive black hole.