Astronomers have identified an ultrafast star traveling at a blistering 6 million km/h, after being ejected by the supermassive black hole at the heart at the Milky Way five million years ago. This star is moving at such speed it will leave the galaxy, and rocket into intergalactic space.

The discovery of the star, known as S5-HVS1, was led by Sergey Koposov from Carnegie Mellon University with a team of collaborators around the world, including Denis Erkal at the University of Surrey, as part of the Southern Stellar Stream Spectroscopic Survey (S5). Located in the constellation of Grus – ‘the Crane’ – S5-HVS1 was found to be moving ten times faster than most stars in the Milky Way.

Astronomers have wondered about high velocity stars since their discovery only two decades ago. S5-HVS1 is unprecedented due to its high speed and close passage to the Earth, “only” 29,000 light years away. With this information, astronomers could track its journey back right into the centre of the Milky Way, where a four million solar mass black hole, known as Sagittarius A*, lurks.

“This is very exciting, as we have long suspected that black holes can eject stars with very high velocities. However, we never had an unambiguous association of such a fast star with the Galactic Centre,” said Sergey Koposov, the lead author of this work. “We think the black hole ejected the star with a speed of thousands of kilometres per second at about the time when humanity’s ancestors were just learning to walk on two feet.”

Superfast stars can be ejected by black holes via the Hills Mechanism, proposed by astronomer Jack Hills thirty years ago. Originally, S5-HSV1 lived with a companion in a binary system, but they strayed too close to Sagittarius A*. In the gravitational tussle, the companion star was captured by the black hole, while S5-HVS1 was thrown out at extremely high speed.

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Source: “Hyper-fast star spotted after ejection by our galaxy’s supermassive black hole”, University of Southampton