A dangerous dance: Alberta astronomers spot star orbiting closest to black hole

On the edge of the milky way, a star circles an all-consuming black hole in the tightest orbit known to man.

Some 14,800 light-years away, the white dwarf star orbits a stellar-mass black hole twice every hour at a distance of around 2.5 times that of Earth to the moon, a new study from the University of Alberta reveals.

It's the closest orbital dance of its kind ever detected, but it's a dangerous one — if the tiny star gets too close, it could be obliterated by the black hole's insatiable appetite.

'Path into oblivion'

"This white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in," the newly-published study's lead author, Arash Bahramian, said in a statement.

"Luckily for this star, we don't think it will follow this path into oblivion, but instead will stay in orbit." 

Astronomers have known about the stellar couple for many years, but researchers always thought they were a pair of stars.

It wasn't until 2015 that radio observations revealed that the pair likely contains a black hole, which is devouring material from the companion star.

'The white dwarf may completely evaporate one day'

Researchers relied on two of NASA's space-based telescopes — the Chandra X-ray Observatory as well as NASA's NuSTAR telescope — and the Australia Telescope Compact Array (ATCA) on the ground to make the discovery.

The extraordinarily close stellar pairing, also known as X9,  is located in a dense cluster of stars called the 47 Tucanae, which is about 14,800 light years away from Earth.

Although the white dwarf does not appear to be in danger of falling in or being torn apart by the black hole, its fate is uncertain.

"Eventually so much matter may be pulled away from the white dwarf that it ends up becoming an exotic kind of planet," said Craig Heinke, an associate professor in the Department of Physics who helped lead the international team investigating the phenomenon.

"Or, the white dwarf may also completely evaporate one day."

Their findings have been published in the Monthly Notices of the Royal Astronomical Society. The study, The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9, is also available online.