Rare X-rays from white-dwarf explosion spotted by chance

Astronomers have made the first observations of X-rays being emitted from a white-dwarf star that has burst into life while stripping material from a companion star. 

The X-rays were emitted by the white dwarf YZ Reticuli 11 h, which is located over 8800 light-years from Earth. Remarkably, the observation was made by chance – but previous research allowed the scientists to understand what they had seen.

We were quite lucky that eROSITA was pointed to the right patch of the sky at the right moment,” König, lead author of a Nature paper describing the discovery, tells Physics World. “For over 30 years it has been postulated that novae should show X-ray flashes.

 These flashes are a direct consequence of the fusion process, a so-called thermonuclear runaway, that occurs on the surface of the white dwarf.”

König explains that X-rays from such an event should be emitted briefly, just before the white dwarf brightens with visible light. The spectral distribution of these X-rays is expected to resemble that of a black body. 

The team found that there was no X-ray source detected by eROSITA  both four hours before and four hours after the event meaning the bright flash must have lasted less than six hours. 

 This is in good agreement with theoretical models, and this told the team they had indeed spotted an X-ray flash from the nova explosion for the first time.

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