- 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.