Tuesday , April 20 2021

A white dwarf star, unexpectedly released by Supersoft X-Ray



The discovery of a white dwarf star that emits supersonic X-rays questiones the usual wisdom about how X-rays are produced by dying stars.

When stars are exhausting fuel after millions of years, they are reduced to a smaller size and become much weaker, in a phase known as a white dwarf. The mass of the star remains unchanged, but the size becomes much smaller, so these dwarfs have very strong gravity. White dwarfs are often found in pairs called binary systems, and their heavy weight means that they can extract matter from the stars of their satellites.

One such system was identified by NASA's Chandra X-ray Observatory project, which detected unusual X-ray emissions from a white dwarf binary system called ASASSN-16oh. As a rule, the star should produce low-energy X-rays, which are called X-ray rays. But the ASASSN-16oh white dwarf emit X-rays, which are much brighter than expected, earning an unusual classification that they are the source of "super-layered" X-rays.

Excessive X-rays indicate that a white dwarf should have a temperature of several hundred thousand degrees, which is hotter than ordinary stars. However, this high temperature is only at certain points on the surface of the star. Astronomers believe that this may be because ASASSN-16oh quickly pulls out material from its red giant satellite, and this issue becomes hot and hot as it's spiral to the white dwarf. The hot gas stays on the accretion disk (a disk of a material that spins around the star), where it eventually merges with the surface of the star and produces X-rays. However, since this process takes place at different speeds, there are several times when the matter flows faster, and the star temporarily produces more vivid X-rays.

Chandra white dwarf supersoft xray
Illustration of a white dwarf star drawing of matter from the red giant. NASA

It was previously thought that ultra high X-rays were observed only when there was a nuclear fusion in white dwarfs. But in the case of ASASSN-16oh, the uneven distribution of X-rays in addition to the optical light released very weak indicates that the merger does not occur in this star. "Our result is in contradiction with the ten-year consensus on how excessive X-ray emissions from white dwarfs are produced," said Thomas Nelson of the University of Pittsburgh. "Now we know that X-rays can be made in two different ways: by nuclear fusion or by increasing matter from the satellite."






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