Milky Way’s supermassive black hole flings star across the galaxy

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  Last updated November 29, 2019 at 9:06 am

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A star has been yeeted by the supermassive black hole at the centre of our galaxy like a drunk ejected by a club bouncer.


supermassive black hole_milky way_star

An artist’s impression of the Milky Way’s supermassive black hole flinging the star from the galaxy’s centre. Credit: James Josephides (Swinburne Astronomy Productions).




Why This Matters:  We’re watching a star that originally lived in the very centre of the Milky Way on its way to depart the galaxy.




A star travelling through the Milky Way at more than six million km/h has been discovered by a team of international astronomers.


They predict that the star was flung from the centre of our galaxy by a supermassive black hole around five million years ago.


The star will leave the Milky Way, never to return


Gary Da Costa, an astronomer at The Australian National University (ANU), says the star is moving so fast that it will leave the Milky Way in about 100 million years, never to return.




Teach This: Education Resource – Milky Way’s supermassive black hole flings star across the galaxy




“We traced this star’s journey back to the centre of our galaxy, which is pretty exciting,” he says.


“This star is travelling at record-breaking speed – 10 times faster than most stars in the Milky Way, including our Sun.


“In astronomical terms, the star will be leaving our galaxy fairly soon and it will likely travel through the emptiness of intergalactic space for eternity. It’s great to be able to confirm a 30-year-old prediction that stars can be flung out of a galaxy by the supermassive black hole at its centre,” Da Costa says.


The giant black hole at the centre of the Milky Way, Sagittarius A*, has a mass equivalent to more than four million Suns.




Deeper: What are black holes?




Da Costa and his ANU colleagues Dougal Mackey and Thomas Nordlander were involved with the study, which was led by Sergey Koposov from Carnegie Mellon University as part of the Southern Stellar Streams Spectroscopic Survey.


The survey also involved astronomers from Australian universities including ANU, Macquarie University, the University of Sydney and UNSW, as well as researchers from the US, UK and Chile.




Black holes can capture and then slingshot stars


Mackey says the team spotted the fast-moving star serendipitously while searching for the shredded remains of small galaxies orbiting the Milky Way.


“The star is only 29,000 light years away, quite close by galactic standards, which means the team could measure its trajectory very precisely,” he says.


Nordlander says supermassive black holes can slingshot stars by interacting with a binary stellar system, whereby two stars orbit around each other.




Also: Spinning supermassive black hole rips a star apart




“If such a binary system approaches a black hole too closely, the black hole can capture one of the stars into a close orbit and kick out the other at very high speed.”


The team discovered the star using the 3.9-metre Anglo-Australian Telescope at the ANU Siding Spring Observatory. The facility’s 2dF instrument is the best in the world for studying the sparsely distributed stars in the outskirts of the Milky Way, due to its ability to obtain simultaneous measurements for up to 400 targets at a time.


Follow-up observations made with the ANU 2.3 metre telescope played an important role in confirming the star’s extreme speed.


The results of the study are published in the Monthly Notices of the Royal Astronomical Society.


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