Key Takeaways:

  • A star, S5-HVS1, is rocketing out of the Milky Way at record speed (1700 km/s) after encountering the galaxy’s central black hole.
  • S5-HVS1 was once part of a double star system that ventured too close to the black hole. One star was captured, the other flung out.
  • This event confirms a theory proposed 30 years ago where a black hole can slingshot stars at extreme speeds.
  • S5-HVS1 will leave the Milky Way in 100 million years and roam interstellar space forever.
  • Astronomers stumbled upon S5-HVS1 while observing other objects, highlighting the element of chance in scientific exploration.

Astronomers have spotted a star heading out of the Milky Way at more than 6m km/h (3.7m mph), or 1,700km per second, after an encounter with the supermassive black hole at the centre of the galaxy.

The star is traveling so quickly that it will leave the Milky Way and sail through interstellar space on its own for the rest of its life in about 100 million years. This is the first recorded instance of a black hole shooting stars out of the galaxy at speeds never before seen, despite predictions made thirty years ago that they could do so.

The Australian National University (ANU) in Canberra is home to astronomer and emeritus professor Gary Da Costa. He said, “We traced this star’s journey back to the centre of our galaxy, which is pretty exciting.”

According to Da Costa and colleagues, the star was a component of a binary star system that orbited very near to Sagittarius A*, the location of the Milky Way’s central black hole, which has a mass of more than 4 million suns, five million years ago.

As the twin stars spiralled inwards, at some point the closer of the two switched into a binary partnership with the black hole that would ultimately end in it being gobbled up and disappearing into oblivion. The dynamics of this interaction resulted in the original partner being ejected at extremely high speed.

The process is known as the Hills mechanism, after the astronomer Jack Hills who proposed the scenario more than 30 years ago.

“This star is travelling at record-breaking speed, 10 times faster than most stars in the Milky Way, including our sun,” said Da Costa. “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.”

S5-HVS1, as the star is known, is the third-fastest star ever observed. The other two had been propelled to great speeds during supernova explosions.

“Excluding these somewhat special cases, this star is far and away the fastest ever spotted,” said Dougal Mackey, a co-author also at ANU College of Science.

Using the 3.9-meter Anglo-Australian Telescope at the ANU Siding Spring Observatory, the team made the star’s discovery. The team made the accidental discovery of S5-HVS1 while observing star streams in the Milky Way halo that are coasting towards the galactic disk and had some spare capacity to look at other stars.

The star will keep going on its journey through intergalactic space after leaving the Milky Way. Da Costa predicted that it would continue and eventually become a white dwarf similar to our sun, with no neighbors.

The study’s findings are released in the Royal Astronomical Society’s Monthly Notices.

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