Astrophysicists observe for the first time an X-ray explosion on a white dwarf

The eROSITA X-ray telescope of the Max Planck Institute for Extraterrestrial Physics installed on the orbital

station "Spektr-RG", scans the sky into the sky insearch for soft X-rays. On July 7, 2020, the telescope recorded a powerful flash that illuminated the detectors of the observation system in a region of the sky in which nothing was visible four hours before. When we passed this part of the sky again after four hours, the radiation disappeared. The entire outbreak lasted less than eight hours.

The researchers note that such x-raysbursts were theoretically predicted more than 30 years ago. However, they have never been directly observed before. The short duration and unpredictability of the event means that such an explosion can only be observed by chance.

The challenge is not only a shortthe duration of this X-ray flash, but also the fact that the spectrum of the emitted radiation is very soft. Soft X-rays are not very energetic and are easily absorbed by interstellar matter, so in this wavelength range we cannot see very deep into space.

Viktor Doroshenko, astrophysicist at the University of Tübingen, one of the authors of the study

Astrophysicists explain that explosive balls fromX-rays are formed on the surface of white dwarfs. If there is a more active companion next to such an old and superdense star, some of the material from the young star flows to the white dwarf. Over time, this hydrogen can accumulate into a layer only a few meters thick on the surface of a ball of oxygen and carbon.

Accumulated gas under pressureexplodes, causing a powerful flash. Such explosions are known as nova explosions, and they can be observed in visible light, but the very beginning of the formation of an explosion in X-rays could not be fixed before.

“The problem in this case was thatafter 30 unsuccessful years of searching for such X-ray flashes, we suddenly saw such a bright event that illuminated the telescope's detectors and complicated the interpretation of the data,” Doroshenko adds.

The researchers used the simulation torestore the overexposed image. The results showed that the white dwarf must be large enough to have a mass comparable to that of the Sun. The explosion, according to scientists, created a fireball with a temperature of 327,000 degrees, which is about sixty times more than the sun.

Astrophysicists note that since such a newlacking energy, they cool rapidly and the X-rays become softer until they finally become visible light, which also reached Earth half a day after the discovery of eROSITA and was observed with optical telescopes.

Cover image: Annika Kreikenbohm, Universität Tübingen

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