S301: Milky Way’s Fastest Star Skims the Central Black Hole

Astronomers have found S301, the Milky Way’s fastest star, zooming around the central black hole Sagittarius A* at about 25,000 km/s on a tight 8.7-year orbit, coming within roughly 12 AU of the hole. Its extreme proximity could enable a direct measurement of the black hole’s spin and a stringent test of Einstein’s general relativity, using the ESO Very Large Telescope Interferometer to track the orbit back to 2017 and observe the 2031 pericentre passage; spin measurements could come within a decade.