Astronomers detect fastest known star in Milky Way

Astronomers have detected the fastest known star in the Milky Way, hurtling around the supermassive black hole at the heart of the galaxy. The star, called S301, travels at about 25,000km (15,500 miles) per second, 100,000 times faster than a commercial plane. It is also the closest known star to the Milky Way’s central black hole, Sagittarius A*, approaching it around the distance of Saturn to the Sun. “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 (MPE) in Garching, Germany, and an author of the study published on the findings. The star’s extreme proximity to Sagittarius A* means that it could open a new window on to the black hole’s fundamental properties and the extreme environment surrounding it. Like many objects in the night sky, black holes are predicted to spin. According to Einstein’s general theory of relativity, a spinning black hole drags spacetime along with it, warping the orbits of surrounding stars. This effect is only meaningful for objects orbiting fast-rotating black holes at close range. S301 appears to have the perfect combination of a highly eccentric (lopsided) 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 of the study, which is published in the journal Nature. Previously it had been assumed it would require measuring the motion of multiple stars for several decades to estimate the spin of Sagittarius A*. The scientists were able to trace S301’s orbit back to 2017 and, by tracking it through its next closest passage in 2031, hope to have enough data. “With this star …