Astronomers discover fastest star orbiting Milky Way's black hole

Astronomers have discovered S301, the fastest known star in the Milky Way, orbiting the supermassive black hole Sagittarius A* at up to 25,000 kilometers per second—about 8% of the speed of light. The finding, published in Nature, could allow scientists to measure the black hole's spin and test Einstein's theory of general relativity in an extreme environment. Source: Excelsior Source: Gizmodo

The discovery

S301 was detected using the Very Large Telescope Interferometer (VLTI) and its GRAVITY+ instrument at the Paranal Observatory in Chile. It completes an orbit in just 8.7 years, coming as close as 12 times the Earth–Sun distance to the black hole. Source: Excelsior Source: Infobae The star's extreme orbit causes spacetime to be dragged and twisted around it, an effect predicted by Einstein's theory. Source: Gizmodo

Why it matters

Until now, the star S2, with a 16-year orbit, was the primary tool for probing the black hole's environment. S301's much closer approach offers a unique opportunity to measure not just the black hole's mass but also its spin—a property that remains largely unknown. Source: Infobae Measuring the spin could help test alternative theories of gravity and the 'no-hair' theorem. Source: Gizmodo

What's next

Astronomers will continue observing S301, which will make its next close approach in 2031. Observing at least two full orbits could allow them to determine the black hole's rotation. Source: Excelsior The star's origin likely involves a binary system torn apart by the black hole's gravity, with the companion star ejected from the galaxy. Source: Excelsior