A Star Orbiting Our Galaxy's Supermassive Black Hole Tests Limits of Relativity

20 hours ago

General relativity is elegant but rarely needed; Newton's gravity suffices for most interactions, including navigating spacecraft and modeling stars orbiting Sag A*.
A newly discovered star, S301, orbits the supermassive black hole Sag A* every 8.7 years with an extremely elliptical orbit, coming within 24 AU at closest approach and moving at over 8% the speed of light.
S301 is the most relativistic star observed, exhibiting significant orbital precession of about 2° per orbit, far greater than Mercury's precession, allowing tests of secondary relativistic effects like gravitational redshift and the transverse Doppler effect.
S301 may help test alternatives to general relativity, especially those that differ at relativistic speeds (order v²/c² or v³/c³), and future telescopes like the GMT could measure higher-order effects.
Observing S301 is challenging due to galactic dust and cloud, and its faintness in infrared; current data is limited to motion, not spectra, but improvements are expected over time.

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