SA telescope confirms new evidence of white dwarf cannibalising companion star

2018-12-04 11:28
An artist’s impression of the supersoft X-ray binary system, ASASSN-16oh, with a small white dwarf star (left) accreting hot gas from its Sun-like companion (right), through an accretion disk. (NASA, CXC, M Weiss)

An artist’s impression of the supersoft X-ray binary system, ASASSN-16oh, with a small white dwarf star (left) accreting hot gas from its Sun-like companion (right), through an accretion disk. (NASA, CXC, M Weiss)

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Work by researchers operating the Southern African Large Telescope (SALT) in the Northern Cape has confirmed that a white dwarf star is cannibalising its companion star.

The find has led astronomers to change their view on how massive radiation bursts occur on white dwarf stars.

The star, ASASSN-16oh, some 200 000 light years from Earth, was initially discovered on December 2, 2016, but additional observation from SALT and other instruments was required to confirm the find.

WATCH: A South African telescope just found a runaway star racing at more than 2 000km a second

Observations of the star showed that it was a "supersoft" X-ray source, produced by gas at temperatures of about 900 000°C.

Such supersoft sources are associated with a runaway thermonuclear explosion on the surface of the white dwarf. They usually occur over a relatively short period of time.

'Fortunate'

"The discovery has shown that there is more than one way for a white dwarf to emit this radiation, nuclear fusion, but now also accretion on to a white dwarf," science engagement officer at the South African Astronomical Observatory Dr Daniel Cunnama told News24.

Astronomers had to act quickly to capture the radiation from the white dwarf.

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"We were fortunate to be able to react quickly to its discovery and undertake crucial observations during the outburst phase," said Dr David Buckley, the principal investigator of the SALT Large Science Programme on transients.

But the data shows that ASASSN-16oh is not a normal supersoft source.

The star is taking material from its red giant companion, which is swirling around it in what astronomers call an accretion disk.

Radiation

The gas from the red giant spirals around the white dwarf and when it falls onto the star, it emits a burst of radiation.

"The transfer of mass is happening at a higher rate than in any system we've caught in the past," said Professor Tom Maccarone, lead author of the ASASSN-16oh discovery paper that appeared in the December 3 issue of Nature Astronomy.

The radiation is an indicator that ASASSN-16oh may end up as a supernova as it consumes more of the red giant's material.

And it won't end happily for any planets that may have been in orbit around the system.

"Any planets in the system would either have been destroyed as the two stars began spiralling toward each other or flung out far from the system," said Cunnama.

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Read more on:    salt  |  saao  |  good news  |  science and technology  |  astronomy
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