Star spotted in closest orbit ever around black hole

Sarah Knapton
X9 binary system with its star and black hole - Nasa 

Astronomers have found evidence of a star that spins around a black hole twice an hour.

It is the closest orbital spin that scientists have ever seen, and was picked up by the two of NASA’s space-based telescopes, the Chandra X-ray Observatory and NuSTAR, and the Australia Telescope Compact Array located in New South Wales, Australia.

The binary system, known as x9,  is located in a dense cluster of stars in the Milky Way known as 47 Tucanae, and is 14,800 light years away from Earth.

Observations from Chandra show the system consistently changes in X-ray brightness every 28 minutes, which is likely the length of time it takes the companion star to make one complete orbit around the black hole.

Along with evidence of large amounts of oxygen in the system, scientists say it makes a strong case that X9 contains a white dwarf star orbiting a black hole at just 2.5 times the separation between the Earth and the Moon.

No star has ever been seen spinning so close to a deadly black hole. 

“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,” said first author Dr. Arash Bahramian, from the University of Alberta in Canada and Michigan State University in the United States.

“Luckily for this star, we don’t think it will follow this path into oblivion - it should stay in orbit.”

The binary system is in a star cluster in the Milky Way galaxy  - Credit:  EUROPEAN SOUTHERN OBSERVATORY 

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.

Associate Professor James Miller-Jones, from Curtin University and ICRAR, said: “We think the star may have been losing gas to the black hole for tens of millions of years and by now has now lost the majority of its mass.”

“Over time, we think that the star’s orbit will get wider and wider as even more mass is lost, eventually turning into an exotic object similar to the famous diamond planet discovered a few years ago,” he said.

Scientists believe that the binary system may have formed when the black hole smashed into a red giant star and as gas from the outer regions of the star were ejected a white dwarf emerged from the debris.

The black hole will eventually suck all of the star's 

Co-author Vlad Tudor, also from the Curtin University branch of ICRAR, said an alternative theory would involve a neutron star that’s being spun up as material is pulled away by the black hole. “Much like a spinning top as you pull the string from around its middle to make it go - but this theory doesn’t explain everything we’re seeing here, so our best current explanation is that we’re dealing with a white dwarf in extremely close proximity to a black hole."

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