Star Discovered In Closest Known Orbit Around A Black Hole

Posted: Mar 14 2017, 12:52pm CDT | by , Updated: Mar 14 2017, 1:07pm CDT, in News | Latest Science News

 

Star Discovered in Closest Known Orbit Around a Black Hole
An artist's impression of a star found in the closest orbit known around a black hole. Credit: X-ray: NASA/CXC/University of Alberta
 

The stellar couple is located in globular cluster 47 Tucanae that is about 14,800 light years away from Earth

Astronomers have discovered an unusual star that is orbiting dangerously close to a nearby black hole. The star is so close to the black hole that it completes a full orbit in just around 30 minutes. This is believed to be the closest ever distance between a black hole and a star rotating around it, making it a stunning discovery on the edge of our galaxy Milky Way. 

“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.” Lead researcher Dr Arash Bahramian from Michigan State University said in a statement.

The black hole and its companion star are located in a dense stellar cluster known as 47 Tucanae and it is roughly 14,800 light years away from Earth. Astronomers have known about the system called X9 for many years but it was not until now that they were able to observe the subtle changes in its orbit.

Using NASA’s Chandra X-ray Observatory, researchers have noticed a constant dip in the brightness of the system every 28 minutes, which is likely the length of time the star takes to pass in front of the black hole and to complete an orbit.

Both objects are likely separated by just 2.5 the distance from Earth to the moon. To put it into perspective, Moon, our nearest neighbour, takes 27 days to complete an orbit around the Earth.

Despite such closeness, the star does not appear to be in danger of falling in or being torn apart by the black hole. Additionally, Chandra has found the evidence for large amounts of oxygen in the system, a characteristic for the presence of a white dwarf. Therefore, a strong case can be made that that the star in question is a white dwarf.

But how did the white dwarf get so close to the black hole? One possibility is that the black hole might have collided with a red giant star at some stage of its life, consuming all the gas around it and turning it into a white dwarf. Then, the white dwarf was brought closer to black hole with its powerful gravitational waves. However, it is just another theory, not actual explanation.

Co-author Vlad Tudor from the Curtin University says. “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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