A new record breaker has been spotted in the Milky Way. Astronomers have seen a white dwarf orbiting so close to a black hole that it goes around the cosmic plughole twice in an hour.
The tightly dancing couple, known as X9, is a binary system located 14,800 light-years from Earth in the 47 Tucanae globular cluster. The presence of a binary system has been known for years but it was only in 2015 that astronomers realized one of the pair was a black hole.
In a paper, published in the Monthly Notices of the Royal Astronomical Society, astronomers describe seeing dramatic changes in the X-ray luminosity of the object every 28 minutes, a telltale signature of a black hole orbited by a very close companion. They also saw an abundance of oxygen in the system that suggested that the companion was an evolved star, likely a white dwarf, slowly being eaten.
“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,” first author Dr Arash Bahramian, from the University of Alberta in Canada and Michigan State University in the US, said in a statement.
The discovery was made possible by combining the power of two NASA space observatories, Chandra and NuSTAR, and the Australian Telescope Compact Array.
The researchers think the black hole has been stealing material for millions of years and the star has lost most of its gas by now. The white dwarf is orbiting about 1 million kilometers (600,000 miles) from the black hole, about 2.5 times the Earth-Moon distance, but it won’t end up like its gas, falling into the jaws of the black hole. In fact, quite the opposite, according to the team.
“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,” co-author Professor James Miller-Jones, from Curtin University and International Center for Radio Astronomy Research (ICRAR) added in the statement.
It’s not just the future of this system that is intriguing, but also its past. The group is trying to work out how this complex system might have formed and they think it might be the consequence of a cosmic collision. The black hole might have hit a red giant star, stripping its outer layers of gas, and essentially turning it into a white dwarf.