Scientists find 2 stars 'thriving' on the brink of a giant black hole

Just on the outskirts of a supermassive black hole roughly 4 million times more massive than the sun, a pair of stars locked in a dance is thriving. 

Astronomers discovered the duo orbiting Sagittarius A*, the Milky Way galaxy's central supermassive black hole, using the European Southern Observatory's Very Large Telescope in Chile. The binary system, the first ever found in the vicinity of an enormous black hole, is dubbed D9.

Black holes are some of the most inscrutable phenomena in space. They don't have surfaces, like a planet or star. Instead, they have a boundary called an "event horizon," or a point of no return. If anything swoops too close, it will eventually fall in, never to escape.

The new discovery, published in Nature Communications, may help astronomers better understand how stars can survive in regions of the cosmos with extreme gravity. The finding also leads scientists to wonder whether such a pair, forming and coexisting near an enormous black hole, could also host exoplanets. 

"Black holes are not as destructive as we thought," said Florian Peißker, one of the researchers at the University of Cologne in Germany, in a statement. 

A binary star system, dubbed D9, was discovered close to the Milky Way's supermassive black hole. Credit: ESO / F. Peißker et al.

Black holes were little more than a theory 50 years ago — a kooky mathematical answer to a physics problem — but even astronomers at the top of their field weren't entirely convinced they existed. 

How the supermassive kind form is even more elusive. Astrophysicists believe these invisible giants lurk at the center of virtually all galaxies. Hubble telescope observations have bolstered the theory that they begin in the dusty cores of starburst galaxies, where new stars are rapidly assembled, but scientists are still teasing that out.

Now black holes are getting their pictures taken by a collection of enormous, synced radio dishes on Earth. Humanity saw a clear view of the Milky Way's own central black hole, Sag A* for short, for the first time in 2022. It is about 26,000 light-years away from Earth.

The James Webb Space Telescope, a collaboration of NASA and the European and Canadian space agencies, is also doing its part to reveal how these mysterious behemoths form in the first place.

The research team found D9 in a dense cluster of stars orbiting Sag A*. Within this group are so-called "G objects," mysterious things that act like stars but look more like clouds of gas and dust. In their paper, the scientists propose that G objects might be a combination of other binary stars and leftover material from other pairs after they've merged, due to the strong gravitational clutch of the nearby black hole. 

That's right: Astronomers suspect the two stars in D9 will soon merge into a single star because of the close-by gravity. They are estimated to be only about 2.7 million years old — for comparison, the sun is 4.5 billion years old — and they'll likely only have another 1 million years or so before they ultimately smash. 

Though no one checked the D9 stars' driver's licenses for their ages, co-author Michal Zajaček, a researcher at Masaryk University in the Czech Republic, said astronomers can tell the pair is young by the gas and dust around them. Other young stars, though not binaries, have been found in this region before.