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12 Dec 2019 7:51
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  •   Home > News > International

    Hypervelocity star ejected from centre of the Milky Way by supermassive black hole

    A breakup of cosmic proportions occurred five million years ago when a binary star system got too close to the supermassive black hole at the centre of our galaxy.

    Forget dejected suitors being sent packing from The Bachelorette finale — a breakup of more cosmic proportions has just been discovered by scientists.

    An international team of researchers have found a hypervelocity star that's been ejected from the centre of our galaxy by the resident supermassive black hole, Sagittarius A*.

    The star — with the catchy moniker S5-HSV1 — is now travelling at more than six million kilometres per hour (or 1,700km/s).

    But the breakup happened five million years ago when it was half of a binary star system that strayed too close to the black hole.

    The two stars were in a very tight orbit around each other, until the black hole cruelly wrenched them apart, capturing one and flinging S5-HSV1 at extremely high speed away from its companion and ejecting it from the centre of our galaxy.

    Could we compare this to a romantic breakup, a la "you didn't receive a rose" Bachelorette-style?

    "If the breakup was sufficient that one party got a lot of energy, I guess so," said astronomer and Emeritus Professor Gary Da Costa of the Australian National University, who is one of the co-authors of the paper published in the Monthly Notices of the Royal Astronomical Society.

    The ejected star got enough energy from the interaction with the black hole that it will be leaving the Milky Way entirely in about 100 million years, and sailing off into the emptiness of intergalactic space never to return, Professor Da Costa said.

    While we've discovered hypervelocity stars before now, we've never been able to unambiguously establish that one has been ejected by the black hole in the centre of the galaxy.

    However S5-HSV1 is relatively close to Earth, a distance of only 29,000 light years away, which has allowed the researchers to trace back its orbit much more accurately.

    "This one, I'll put my hand on my heart and say it comes from the centre of the galaxy," Professor Da Costa said.

    We can use this "exquisite orbit of S5-HSV1" and the fact that it's coming from the centre of the Milky Way as a sort of ruler to measure the galaxy, said lead author of the paper Sergey Koposov of Carnegie Mellon University.

    "If we find more such stars, that should allow us to not only measure the galaxy better, but also measure the mass distribution in the galaxy," Dr Koposov said, including the mysterious dark matter.

    While S5-HSV1 is the first hypervelocity star where we know it came from the galactic centre, it's not the only way such stars can be created, said astrophysicist Holger Baumgardt of the University of Queensland, who wasn't involved in the study.

    When one of the stars in a binary system goes supernova, it can accelerate its companion star to a very high velocity.

    "There's also a breakup involved … the star is set free, but it is a different process," Dr Baumgardt said.

    Let's hope Angie Kent's suitors have better luck on The Bachelorette.

    © 2019 ABC Australian Broadcasting Corporation. All rights reserved

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