Starship Asterisk*

An artist’s impression of S5-HVS1’s ejection by Sagittarius A*, the black hole at the
centre of the Galaxy. The black hole and the captured binary partner to S5-HVS1 are
seen far away in the left corner of the picture, while S5-HVS1 is in the foreground,
speeding away from them. ~ James Josephides (Swinburne Astronomy Productions)

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Astronomers have spotted an ultrafast star, travelling at a blistering 6 million km/h, ejected by the supermassive black hole at the heart at the Milky Way five million years ago. ...

The discovery of the star, known as S5-HVS1, was made 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 – 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 thousand light years away. With this information, astronomers could track its journey back into the centre of the Milky Way, where a 4 million solar mass black hole, known as Sagittarius A*, lurks. ...

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. ...

• Monthly Notices of the RAS (online 04 Nov 2019) DOI: 10.1093/mnras/stz3081
• arXiv.org > astro-ph > arXiv:1907.11725 > 26 Jul 2019 (v1), 11 Nov 2019 (v2)