Galactic-center S Stars as a Prospective Test of the Einstein Equivalence Principle

The S stars in the Galactic-center region are found to be on near-perfect Keplerian orbits around presumably a supermassive black hole, with periods of 15-50 yr. Since these stars reach a few percent of light speed at pericenter, various relativistic effects are expected and have been discussed in the literature. We argue that an elegant test of the Einstein equivalence principle should be possible with existing instruments, through spectroscopic monitoring of an S star concentrated during the months around pericenter, supplemented with an already-adequate astrometric determination of the inclination. In essence, the spectrum of an S star can be considered a heterogeneous ensemble of clocks in a freely falling frame, which near pericenter is moving at relativistic speeds. DOI: https://doi.org/10.1088/2041-8205/734/1/L19 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-48282 Accepted Version Originally published at: Angélil, R; Saha, P (2011). Galactic-center S stars as a prospective test of the Einstein equivalence principle. Astrophysical Journal Letters, 734(1):L19. DOI: https://doi.org/10.1088/2041-8205/734/1/L19 ar X iv :1 10 5. 09 18 v1 [ as tr oph .G A ] 4 M ay 2 01 1 GALACTIC-CENTER S STARS AS A PROSPECTIVE TEST OF THE EINSTEIN EQUIVALENCE PRINCIPLE Raymond Angélil and Prasenjit Saha Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland (Dated: May 6, 2011) Accepted for publication in ApJL