White Dwarf Star Orbits Closest to Black Hole

Star orbiting around black hole

Astronomers discovered a white dwarf star orbiting closest to a black hole

NASA discovered a white dwarf star that performs an interesting dance around a black hole. The star orbits around the black hole twice an hour and creates one of the tightest movements of the type ever witnessed in our Milky Way galaxy.

A star and a black hole are companions

Astronomers spotted the phenomenon with the help of two telescopes, namely the Chandra X-ray Observatory NuSTAR and the Australia Telescope Compact Array from New South Wales. The stellar couple of the star and black hole, called binary, is situated in the globular cluster 47 Tucanae. This cluster lies 14,800 light-years away from Earth.

The existence of the binary has been well-known for many years, but only in 2015 did the astronomers find out that the couple was made up of a black hole which absorbed material from a star. The team that made the discovery gathered researchers from Curtin University and the International Center for Radio Astronomy Research.

They called the system X9. After a thorough analysis with the Chandra telescope, they found that the X-ray brightness of the binary changes every 28 minutes. They established that this is the time that the star needs to complete an orbit around the black hole. The traces of oxygen from the system led the researchers to the conclusion that the star is a white dwarf.

Dr. Arash Bahramian, the main author of the study, made a few statements.

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

The star is not in danger to be absorbed by the black hole, but studies show that it lost most of its gas during the millions of years it orbited around its companion.

How did the black hole acquire a star as such a close companion?

One of the theories suggests a collision between the black hole and a red giant star. This would have caused a massive ejection of gas which would have created the orbiting white dwarf.

A different theory says that the binary does not involve a white dwarf, but a neutron star that gets spun up as material is pulled away from the black hole. However, the scientists said that this theory does not account for all the phenomena visible in the binary, so the final assumption is that the star is a white dwarf.

If you want more information on the matter, you can consult the study published in Monthly Notices of the Royal Astronomical Society.
Image Source: Wikimedia Commons