Relativistic redshift of the star S0-2 orbiting the Galactic center supermassive black hole

Abstract

General Relativity predicts that a star passing close to a supermassive black hole should exhibit a relativistic redshift. We test this using observations of the Galactic center star S0-2. We combine existing spectroscopic and astrometric measurements from 1995-2017, which cover S0-2's 16-year orbit, with measurements in 2018 March to September which cover three events during its closest approach to the black hole. We detect the combination of special relativistic- and gravitational-redshift, quantified using a redshift parameter, $\hat{I}\yen$. Our result, $\hat{I}\yen =0.88\pm 0.17$, is consistent with General Relativity ($\hat{I}\yen =1$) and excludes a Newtonian model ($\hat{I}\yen =0$ ) with a statistical significance of 5 $\ddot{I}ƒ$.

78 pages, 21 figures, accepted to Science, astrometry and radial velocity measurements, and posterior chains available here, http://www.astro.ucla.edu/~ghezgroup/gc/gr/data.zip