Fastest Known Star in the Milky Way Could Unlock Black Hole's Spin
Astronomers have detected the fastest known star in the Milky Way, a body designated S301 that races around the supermassive black hole at the galaxy's center at roughly 25,000 kilometers per second. Its extreme proximity to Sagittarius A could open a new window onto the black hole's fundamental properties and allow scientists to measure its spin for the first time. The discovery was published August 19, 2026, in the journal Nature. S301 is not only the fastest but also the closest known star t
OST Staff · August 19, 2026
Astronomers have detected the fastest known star in the Milky Way, a body designated S301 that races around the supermassive black hole at the galaxy's center at roughly 25,000 kilometers per second. Its extreme proximity to Sagittarius A could open a new window onto the black hole's fundamental properties and allow scientists to measure its spin for the first time.
The discovery was published August 19, 2026, in the journal Nature. S301 is not only the fastest but also the closest known star to Sagittarius A, approaching within roughly the distance of Saturn from the Sun. At its peak it travels at about 8 percent of the speed of light, some 100,000 times faster than a commercial airplane.
The star completes its orbit in just 8.7 years and comes as close as 12 times the Earth-Sun distance to the black hole. "What is special about this star is that it's orbiting Sagittarius A on a very tight orbit, taking just 8.7 years to complete it, and is approaching the black hole at a mere 12 times the distance of Earth to the sun. That is unprecedented," said Felix Mang, a PhD student at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and an author of the study.
According to Einstein's general theory of relativity, a spinning black hole drags spacetime along with it, warping the orbits of surrounding stars. That effect is only meaningful for objects orbiting fast-rotating black holes at close range, and S301 combines a highly eccentric and very tight orbit. "For the first time, we would actually be able to measure very directly the spin of a massive black hole, which would be a key test of Einstein's theory," said Dr Stefan Gillessen, a senior scientist at MPE and a co-author.
The observations were made using the European Southern Observatory's Very Large Telescope Interferometer at the Paranal Observatory in Chile, which combines light from four 8-meter telescopes. Although the star is unusually close to the central black hole, it is not expected to cross the event horizon. "Black holes are perceived as these cosmic vacuum cleaners engulfing everything they can get a handle on," Mang said. "But it's just a massive object. It's not really much different from something orbiting the sun and it's going to remain on this orbit."
The scientists say the star's orbit provides a direct route to measuring the spin of Sagittarius A, a task previously assumed to require tracking multiple stars over several decades. Dr Ziri Younsi, an astrophysicist at University College London who was not involved in the observations, called it "incredibly important as a discovery" and said using the orbit to measure the black hole's spin would be a gamechanger for understanding the evolution of the Milky Way.
Researchers traced S301's orbit back to 2017 and aim to track it through its next closest passage in 2031. "With this star we hope to measure, within the next 10 years, the spin of the black hole," Mang said.