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Star discovered travelling over 1,700 kilometres every second © Swinburne Astronomy Productions/PA

Star discovered whizzing out of the Galaxy at over 1,700 kilometres every second

Published: 12th November, 2019 at 20:00
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The star – known as S5-HVS1 – was found to be moving 10 times faster than most stars in the Milky Way.

Astronomers have discovered an ultra-fast star travelling at more than 6 million kilometres per hour.


It was ejected by the supermassive black hole at the heart of the Milky Way 5 million years ago – around the time human ancestors were learning to walk on two feet.

The star, known as S5-HVS1, was discovered by Sergey Koposov from Carnegie Mellon University as part of the Southern Stellar Stream Spectroscopic Survey (S5). Located in the constellation of Grus – the Crane – it was found to be moving 10 times faster than most stars in the Milky Way at over 1,700 kilometres per second.

Douglas Boubert, from the University of Oxford, a co-author on the study, said: “The velocity of the discovered star is so high that it will inevitably leave the Galaxy and never return.”

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High-velocity stars were discovered 2 decades ago and since then have fascinated astronomers.

Scientists say S5-HVS1 is unprecedented due to its high speed and close passage to the Earth – only 29,000 light years away. Using this information, they were able to track its journey back into the centre of the Milky Way where a 4 million solar mass black hole, known as Sagittarius A*, lurks.

Professor Koposov, lead author of the study, said: “This is super exciting as we have long suspected that black holes can eject stars with very high velocities. However, we never before had a clear association of such a fast star with the Galactic Centre.

“We think the black hole ejected the star with a speed of thousands of kilometres per second about five million years ago. This ejection happened at the time when humanity’s ancestors were just learning to walk on two feet.”

The location of the star on the sky and the direction of its motion © Sergey Koposov/PA
The location of the star on the sky and the direction of its motion © Sergey Koposov/PA

Ting Li, from Carnegie Observatories and Princeton University, and leader of the S5 Collaboration, said: “Seeing this star is really amazing as we know it must have formed in the Galactic Centre, a place very different to our local environment. It is a visitor from a strange land.”

S5-HVS1 was discovered with the 3.9-metre Anglo-Australian Telescope (AAT) near Coonabarabran, New South Wales, Australia, coupled with observations from the European Space Agency’s Gaia satellite that allowed the astronomers to reveal the full speed of the star and its journey.

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.


Sara RigbyOnline staff writer, BBC Science Focus

Sara is the online staff writer at BBC Science Focus. She has an MPhys in mathematical physics and loves all things space, dinosaurs and dogs.


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