Astronomers have found the fastest star in our galaxy – and is close to its black hole that it can feel its rotation.

The star, known as S301, is flying around our Milky Way at speeds of 25,000 kilometres per second as it orbits Sagittarius A*, the black hole at our galaxy’s centre.

It comes closer to that black hole than any other star seen before. As such, scientists believe it “opens a new window to the fundamental properties of spacetime in this extreme black-hole environment”, said Reinhard Genzel, the Nobel Prize-winning director at the Max Planck Institute for Extraterrestrial Physics (MPE).

“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,” says Felix Mang, PhD student at MPE and author of the new study of the black hole.

As it passes closest to the black hole, it reaches speeds 100,000 times faster than a commercial plane, or 8 per cent of the speed of light. That makes it the record holder for the fastest star in our galaxy.

And that is not its only record, since it also orbits the black hole more closely than ever before, at the distance between Saturn and our Sun. Because it comes so close, it could be used to measure the rotation of the black hole.

Scientists believe that our black hole spins, like almost everything else in the universe. Einstein’s general theory of relativity proposes that the spinning black hole pulls spacetime around with it, dragging the orbit of nearby stars.

That means that astronomers could use the star to measure that spin – and better understand a central theory of the universe. “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 MPE researcher Stefan Gillessen, who also worked on the new study.

Scientists found the star using the European Southern Observatory’s Very Large Telescope Interferometer. That is able to combine light from four different telescopes to create a “virtual” telescope with vastly more resolution.

That allowed the researchers to first glimpse the new star in 2023, and they have been watching it ever since, hoping to understand its orbit. They were able to track its journey back to 2017, and found that it made its closest approach to the black hole in early 2023.

The nature of the star, and the fact that scientists believe that stars could not form so nearby to a black hole, suggest that it was once a part of a pair of stars that was ripped apart by Sagittarius A*. The star S301 then became trapped by the black hole’s gravity and the other star was probably kicked out with enough force that it is expected to have been thrown out of the galaxy entirely.

Researchers hope to continue studying the star, including with upcoming telescopes. It will return for its closest approach to the black hole in 2031, which will be a crucial time to better understand the star and its trajectory, which might allow scientists to finally understand the spin of the black hole.

The work is reported in a new paper, ‘Discovery of a star sensitive to the spin of Sgr A’, published in the journal Nature*.