23Dec2012

X-Ray Flash Causing White Dwarf Stars To Appear Like Black Holes

There are always more new mysteries to add to the intrigue of the Cosmos. Black hole theories abound, and here’s a new observation.

Now an incredible observation from the astronomers at the University of Southampton has revealed that bright X-ray flares in nearby galaxies, once assumed to indicate the presence of black holes, can in fact be produced by white dwarfs. 

So what happened? The observation detected an extreme, short-lived x-ray flare that lit up an x-ray telescope located on the International Space Station. Optical telescopes located in South Africa and Chile were quickly turned its way and confirmed the flare, called XRF111111 as it happened on 11 November, 2011, was located in the Small Magellanic Cloud.

It was so incredibly luminous that researchers originally labeled it as a black hole which was producing x-rays. However, further study done by Professor Phil Charles and his team showed it wasn’t running a temperature. In this case, the x-rays were too cool to be a black hole.

So what could it be? Try a white dwarf star. These burned-out denizens of the deep are all that’s left of a normal star similar to our Sun. When they reach this stage in their life, they still contain as much as one solar mass, but squeezed into a volume about the size of Earth.

Even though it was a tidy explanation, it still not considered normal for stars of this type to produce such a huge x-ray flash. Through optical observations, astronomers confirmed the white

A picture of a Binary star system with a white...

A picture of a Binary star system with a white dwarf… (Photo credit: Wikipedia)

dwarf was in orbit around a hot B-type star – a star about 10 solar masses, but much hotter and brighter. Unique? Darn near. This has only been observed twice, and both times with much lower x-ray luminosities. Dr. Charles’ research team has shown the material from the B star to be accreting onto the surface of the white dwarf. This eventually produced a “runaway thermonuclear buring” that was observed from our vantage point 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.” says Professor Charles. “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.”

“We think that this incredible X-ray flash was not due to accretion onto a black hole but was instead 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.

“This surprising result shows that, in the right circumstances, white dwarfs are capable of mimicking black holes, the most luminous objects we know of.”

Original Story Source: University of Southampton News Release”. Reported by Tammy Plotner for “Dave Reneke’s World of Space and Astronomy News”.

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