White dwarfs could imitate blackholes in the release of strong X-ray flares

Astronomers have found that the bright X-ray flares from neighboring galaxies, which were considered to be due to the black holes, are actually the product of white dwarfs.

This research has been published online in The Astrophysical Journal.

The Southampton astronomers studied the short-lived X-ray burst with the help X-ray telescope on the International Space Station. This X-ray flare called XRF111111 occurred on 11 November, 2011, and was produced in Small Magellanic Cloud, which are about 160,000 and 200,000 light years away from us. It can be seen from the Southern Hemisphere.

Large and small magelanic clouds (right) and the Milky Way (Left) above Patagonian Andes (Credit: Miloslav Druckmüller/National Geographic)

Large and small Magelanic clouds (right) and the Milky Way (Left) above Patagonian Andes (Credit: Miloslav Druckmüller/National Geographic) 

MAXI J0158-744/XRF 111111A was very much bright that the astronomers thought that the flare came from a black hole but in the recent research astronomers found that the X-ray temperature was so low that the flare was produced by a white dwarf instead of black hole. White dwarfs are small, extremely dense stars with nearly the mass of the sun in a volume of Earth. These stars are in the final stages of evolution.

This white dwarf has been found to be orbiting around a hot B star. Researchers are of the opinion that the material from the B star accumulated on the white dwarf that underwent huge thermonuclear burning shown on Earth as a nova explosion.

Professor Charles said in a statement, “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.

“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.”

Reference:

Li, K., Kong, A., Charles, P., Lu, T., Bartlett, E., Coe, M., McBride, V., Rajoelimanana, A., Udalski, A., Masetti, N., & Franzen, T. (2012). A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158-744 The Astrophysical Journal, 761 (2) DOI: 10.1088/0004-637X/761/2/99