Relativity Goes Extreme: Star S301 Dances Close to the Milky Way’s Black Hole

Astronomers have found star S301, a Sun-like star in the highly elliptical 8.7-year orbit around the Milky Way’s central supermassive black hole Sag A*, approaching within about 24 AU at closest approach and reaching speeds near 0.08c. The orbit shows relativistic precession of about 2° per pass, along with gravitational redshift and transverse Doppler effects, enabling tests of general relativity and potential constraints on alternative gravity theories. While dust and faintness hinder spectral data today, future observatories like the Giant Magellan Telescope could measure higher-order relativistic effects, further probing gravity near a black hole.