Star S301 Orbits Sag A* Every 8.7 Years, Advancing 2° per Loop
Updated
Updated · Universe Today · Jul 20
Star S301 Orbits Sag A* Every 8.7 Years, Advancing 2° per Loop
2 articles · Updated · Universe Today · Jul 20
Summary
S301 circles the Milky Way’s central black hole in just 8.7 years, making it the shortest-period known S-star and the most relativistic star yet observed.
At closest approach, the Sun-like star comes within about 24 AU of Sag A* and exceeds 8% of light speed, producing a perihelion shift of roughly 2° each orbit.
That extreme motion gives astronomers a rare natural test bed for gravitational redshift, the transverse Doppler effect and higher-order relativistic effects tied to the black hole’s spin.
Future giant telescopes such as the Giant Magellan Telescope could measure those second- and third-order signals, helping probe alternatives to general relativity that diverge only in extreme regimes.
For now, dust around the galactic center and S301’s faint infrared output limit spectral measurements, so researchers can track its motion more easily than its detailed light signature.
Could a star traveling at 8% light speed finally reveal a flaw in Einstein's theory of gravity?
What secrets about gravity might be unlocked by this star as it orbits the Milky Way's supermassive black hole?
S301’s 8.7-Year Orbit Around the Milky Way’s Black Hole: Unlocking Extreme Relativity and Stellar Origins
Overview
S301 is a remarkable star discovered by Stefan Gillessen’s team using the GRAVITY instrument on the Very Large Telescope. It orbits the supermassive black hole Sagittarius A* at the center of our galaxy, marking a major step in understanding this extreme environment. S301 is about 1.5 times the mass of the Sun and stands out for its record-breaking short orbital period of 8.7 years. Its orbit is highly elliptical, bringing it as close as 24 astronomical units to the black hole, where it reaches speeds of 25,000 kilometers per second—over 8% the speed of light.