Stellar rotation as a new observable to test general relativity in the Galactic Center

S stars in the Galactic Center are excellent testbeds of various general relativistic effects. While previous works focus on modeling their orbital motion around Sgr A*-the supermassive black hole in the Galactic Center-here we explore the possibility of using the rotation of S stars to test the de Sitter precession predicted by general relativity. We show that, by reorienting the rotation axes of S stars, de Sitter precession will change the apparent width of the absorption lines in the stellar spectra. Our numerical simulations suggest that the newly discovered S4714 and S62 are best suited for such a test because of their small pericenter distances relative to Sgr A*. Depending on the initial inclination of the star, the line width would vary by as much as 20-76 km s(-1) within a period of 20-40 years. Such a variation is comparable to the current detection limit. Since the precession rate is sensitive to the orbital eccentricity, monitoring the rotation velocities could also help us better constrain the orbital elements of the S stars.

Automated summary

S stars in the Galactic Center are ideal test objects for studying general relativistic effects, and while previous research has focused on testing their orbital motion around a supermassive black hole, this study explores using their rotation to test de Sitter precession. Numerical simulations suggest that the recently discovered S4714 and S62 may be best suited for such a test, as their rotation could reveal changes in absorption lines in stellar spectra.