U of A astronomers discover closest known star in orbit of a black hole

Arash Bahramian, a doctoral student from the University of Alberta, has made an important astronomical discovery.

In a neighbourhood of our galaxy called 47 Tucanae, a little under 15,000 light years away, there is a dense cluster of stars that exhibit something highly unusual.

A white dwarf star called X9 is orbiting a black hole very quickly, almost twice as fast as any others are previously known to.

“In 28 minutes, the time it takes you to watch an episode of the Big Bang Theory,” explained Gregory Sivakoff, an assistant professor at the U of A department of physics, and co-author of the study.

But that’s not the only thing that has his team excited.

“We have never seen an object orbiting around a potential black hole this closely before in our galaxy, so that’s one reason it’s so interesting,” said Sivakoff.

“But it’s also an object that would be very hard to explain, which is the thing that scientists love. The harder it is to explain something, normally the more interesting it is.”

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Everything about this discovery is a little hard to explain, but we’ll try. First, what is a white dwarf anyway?

“They’re basically what the sun will wind up as, as it runs out of fuel,” Sivakoff said. “So stars like our sun will collapse into something roughly the size of the earth without loosing much mass.”

This suspected white dwarf is about the size of the planet Neptune, and exhibits characteristics astronomers would expect – like having a large amount of oxygen nearby. It’s orbiting around the black hole at a distance of 2.5 times that of Earth to our moon.

“The gravity from the black hole is pulling off some of the outer bits of the white dwarf, and that’s how we can see the x-ray emission from that,” Sivakoff said.

Sivakoff’s team used NASA’s Chandra X-ray Observatory, among other instruments, that aided in the discovery.

So will this white dwarf, travelling at 5,000,000 km/h, meet a certain demise and be sucked into oblivion?

Apparently not.

“Because you are transferring matter from the white dwarf to the black hole, the white dwarf is slowly moving away from the black hole,” Sivakoff said, adding that’s another aspect of the findings that will intrigue researchers.

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Sivakoff said it’s these types of novel discoveries that unite the scientific community in their quest for answers. Physicists from around the world may look at the U of A data and offer opposing theories, or compound the U of A theories with more supporting evidence.

“This pushes basically the envelope of our understanding,” Sivakoff continued.

“We really haven’t seen a system like this — and the explanations I think are going to be a little bit exotic. And the exotic situations I think are the ones where we learn the most about physics, and our universe that we live in.”