The fastest star in our galaxy moves at 8 per cent the speed of light

2020-08-14

Astronomers have spotted the fastest star ever, moving at 8 per cent of the speed of light. The star, called S4714, orbits close to the supermassive black hole at the centre of the Milky Way and could be the best place in the galaxy to test Albert Einstein’s theory of general relativity.

It is hard to spot stars orbiting Sagittarius A*, the Milky Way’s central black hole, because the galaxy gets increasingly crowded the closer you get to its middle. Florian Peissker at the University of Cologne in Germany and his colleagues used the Very Large Telescope (VLT) in Chile to observe the galactic centre and the stars there.

They spotted five new stars orbiting close to Sagittarius A*, including S4714. It is more extreme than the others: its elliptical orbit takes it to a distance from the black hole that is just 12.6 times the size of the space between Earth and the sun. It moves at a speed of nearly 24,000 kilometres per second – 8 per cent the speed of light – which makes it the fastest-moving star we have ever seen.

The view from such a star would be extreme. “The night sky would be awash with bright nearby stars, the whole sky just filled with stars,” says Jessica Lu at the University of California, Berkeley. “Even Sagittarius A* wouldn’t look like a big black hole, it would just look like a bright star because of all the material being accreted.”

You would be able to see not only the colossal black hole and the bright disk of matter falling into it, but also the strange effects of light stretching and warping around it, says Peissker.

These occur because of general relativity, a theory that describes the inner workings of gravity. The area near Sagittarius A* is the best place in the Milky Way to test that theory because the black hole’s gravity is so powerful. S4714 gets closer than any other star, making it an ideal laboratory for such tests, says Peissker.

However, some of these will have to wait for the next generation of more powerful telescopes, says Lu. “With the next generation of telescopes, it might be a player, but I think right now it’s just too faint.”

newscientist.com, 14 August 2020
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