December 18, 2012
Astronomers Observe White Dwarfs Imitating Black Holes
Lee Rannals for redOrbit.com — Your Universe Online
The team made the discovery by detecting a dramatic, short-lived X-ray flare that was picked up by an X-ray telescope on the International Space Station (ISS).
Astronomers used optical telescopes in South Africa and Chile to help observe the flare, called XRF111111, on November 11, 2011.
The flare was so luminous that astronomers initially thought it was a black hole producing X-rays. However, further research showed that its X-ray temperature was so low it had to be a white dwarf.
White dwarfs are not considered capable of producing such a huge X-ray flash, but the optical observations showed that the star was orbiting a hot B star, which is a normal star about 10 times the mass of our Sun.
The researchers revealed that material was probably collecting on the surface of the white dwarf from the B star, and eventually underwent runaway thermonuclear burning that was seen on Earth as a nova explosion.
“Our observations show that the thermonuclear burning probably caused a shell of matter to be ejected from around the white dwarf and when the shell hit the hot wind of the B star it produced a huge shock leading to the X-ray flash that was seen on the International Space Station," Professor Phil Charles, a researchers on the project, said in a statement.
He said that the team believes this X-ray flash was not due to accretion onto a black hole, but was due to a nova explosion on a white dwarf that took place close to a hot massive star.
"This was something that we, as astronomers, have never seen before," said Charles. “This surprising result shows that, in the right circumstances, white dwarfs are capable of mimicking black holes, the most luminous objects we know of," he added.