Astronomers Find S301 Racing at 25,000 km/s Around Sagittarius A* as 2031 Test Nears
Updated
Updated · ScienceAlert · Aug 19
Astronomers Find S301 Racing at 25,000 km/s Around Sagittarius A* as 2031 Test Nears
3 articles · Updated · ScienceAlert · Aug 19
Summary
S301 circles the Milky Way’s central black hole every 8.7 years and reaches more than 25,000 km/s—about 8.5% of light speed—making it the fastest known star on such an orbit.
That extreme path carries S301 roughly 10 times closer to Sagittarius A* than the well-studied star S2, into a region where frame-dragging from the black hole’s spin should subtly distort its orbit.
Tracking those distortions could let astronomers measure Sagittarius A*’s spin and later its quadrupole moment, key steps toward testing the black-hole no-hair theorem.
S301’s highly elongated orbit also hints it may be the captured survivor of a binary torn apart by the black hole, with a former companion potentially flung outward at high speed.
Its next closest approach comes in late 2031, when the spin signal should be strongest; GRAVITY+ and ESO’s upcoming Extremely Large Telescope aim to pin down the black hole’s spin within a decade.
Will mysterious Newtonian forces trick astronomers, or will S301 finally reveal the true spin of our supermassive black hole?
Racing at extreme speeds, could S301's warped orbit rewrite Einstein's theories of relativity during its 2031 close approach?
Could the fastest star in our galaxy actually be the abandoned twin of a banished hypervelocity star?
S301: The Fastest Star Ever Found Near Sagittarius A* Unlocks Black Hole Spin and Einstein’s Limits
Overview
In August 2026, astronomers using the GRAVITY+ instrument at the Very Large Telescope Interferometer announced the discovery of S301, the fastest known star orbiting the Milky Way’s central black hole, Sagittarius A*. S301 was likely captured after its original binary companion was ejected by the black hole’s gravity, leaving it in a highly elongated orbit that brings it extremely close to the black hole. This close approach exposes S301 to intense tidal forces and allows its orbit to reveal subtle effects of Einstein’s relativity, including frame-dragging. By tracking S301’s path with next-generation observatories over the next decade, scientists aim to directly measure the black hole’s spin and test fundamental theories about black holes and dark matter.