How white dwarfs mimic black holes

December 17, 2012
How white dwarfs mimic black holes
X-ray flash of XRF111111

(—A remarkable observation by astronomers from the University of Southampton has been published in one of the world's foremost astrophysics research journals.

The research by Professor Phil Charles, Professor Malcolm Coe and postgraduate student Liz Bartlett has appeared in The that is devoted to recent developments, discoveries, and theories in .

The Southampton Physics and Astronomy team are part of a - with colleagues in Taiwan, South Africa, Poland, Australia and Italy - that has revealed that bright X-ray flares in , once assumed to indicate the presence of black holes, can in fact be produced by white dwarfs.

They made the discovery by detecting a dramatic, short-lived X-ray flare that was picked up by an X-ray telescope on the .

Using in South Africa and Chile, the Southampton astronomers showed that the flare, called XRF111111 as it happened on 11 November, 2011, was located in the . These are between 160,000 and 200,000 light years away and are the nearest to the Milky Way. They are visible to the naked eye from the Southern Hemisphere.

The flare from XRF111111 was so luminous that astronomers initially thought it was likely to be a black hole producing X-rays but further research by Phil and his team revealed that its X-ray temperature was so low that it had to be a white dwarf instead.

White dwarfs are very common, burnt-out cinders of normal stars like the Sun that are typically about one solar mass but are contained in a volume no bigger than the Earth.

However, white dwarfs were not considered capable of producing such a huge X-ray flash but the optical observations in South Africa and Chile showed that the white dwarf was orbiting a hot B star - a normal star about 10 times the mass of our Sun that is much hotter and brighter. This was something that had only been seen twice previously and both times with much lower X-ray luminosities.

Research by Professor Charles and his team 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.

Professor Charles says: "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, are capable of mimicking black holes, the most luminous objects we know of."

A paper led by Ray Li, from the National Tsing Hua University, in Taiwan, describing these new results will appear in the 20 December issue of The Astrophysical Journal.

Explore further: Binary white dwarf stars

More information: K. L. Li, Albert K. H. Kong, P. A. Charles, Ting-Ni Lu, E. S. Bartlett, M. J. Coe, V. McBride, A. Rajoelimanana, A. Udalski, N. Masetti, and Thomas Franzen, A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158-744, ApJ 761 99 doi:10.1088/0004-637X/761/2/99

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3 / 5 (4) Dec 17, 2012
This surprising result shows that, in the right circumstances, white dwarfs are capable of mimicking black holes, the most luminous objects we know of.

Black hole accretion disks produce energy at all frequencies. They didn't say if the above object was luminous in anything except xray. Based on their explanation theorizing that a shock wave was the source of the xrays then it should only have been mostly xrays rather than full spectrum.
Shinichi D_
5 / 5 (3) Dec 17, 2012
The progenitor of the white dwarf must have been even more massive than its companion, to go through the main sequence. Shouldn't it become a neutron star? Or a supernova? What is roughly the most massive star that can produce a WD?
5 / 5 (3) Dec 17, 2012
The Chandrasekhar limit is 1.44 solar masses. Above this level, a star's condensing mass can overcome electron degeneracy pressure and form a neutron star.
5 / 5 (1) Dec 17, 2012
Perhaps the two stars formed separately, then came to orbit each other later? Otherwise, agreed, no white dwarf should orbit a much larger companion still in main sequence if the two formed together, since the larger star should burn out first.
2.1 / 5 (7) Dec 17, 2012
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
IMO the similar things may happen with more massive stars and black holes and after then an electroweak burning of neutrinos and/or axions may happen under temporal formation of bosenova. Recently we could even read a theory for it right here at PhysOrg, so you can see, it's not just a random idea of my peculiar mind. This essentially provides the mechanism for occasional gamma ray bursts, as observed around many black holes, including the central black hole of Milky Way. These bursts were conjectured before twenty years already with French astronomer LaViolette. I do consider these bursts as one of probable scenarios of global warming events.
2.1 / 5 (7) Dec 17, 2012
Here are various indicia of neutrino atmosphere around Sun, which appears like thick ring, ejecting the neutrinos from solar core in thick jets. The neutrinos influent the speed of radioactive elements decay, which has been observed during flyby of few spaceprobes. It would indicate, that the dark matter is distributed around Sun in similar way, like around massive galactic clusters.

If we estimate the mean velocity of neutrinos, which are in thermodynamic equilibrium with CMBR radiation of 3K temperature), you'll get a velocity, which is quite close to the escape velocity of Sun (560 km/sec, or so). So it may be possible, that the solar neutrinos cumulate and condense around Sun like the sparse invisible atmosphere and they occasionally collapse into it under formation of solar flares. This event may be triggered, when the Sun appears in the gravitational shadow of multiple massive bodies, i.e. during eclipses and/or planetary conjunctions.
2.1 / 5 (7) Dec 17, 2012
The ejection of neutrinos during solar flares may even influence the motion of plasma outside of Sun, as some observations indicate. I presume, the neutrinos ejected from Sun during flares accelerate the decay of radioactive elements inside of Earth crust and they cause heat waves there, which may result into quakes. In this way, the processes beneath the surfaces of both massive bodies are mutually connected through antimatter particles (negative curvature of space-time) in similar way, like the processes above their surfaces, where the space-time curvature is positive (climate changes induced with solar wind).

Apparently, there is still lotta physics to research...
1 / 5 (3) Dec 18, 2012
"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."

Yes, likely something similar happens on the galactic supermassive core stars, as LaViolette contends.

BTW, Val, LaViolette is American. He once worked for the US PTO, as an examiner.

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