Thursday , January 21 2021

The White Dwarf star unexpectedly emits Supersoft X-rays

The discovery of a white dwarf star radiating rays of supersoft casts doubt on the conventional wisdom of how the X-rays are produced by dying stars.

When stars run out of fuel after millions of years, they shrink to a smaller size and become much weaker in a phase known as a white dwarf. The mass of the star remains the same, but the size becomes much smaller, so these dwarves have very strong gravity. The White Dwarf often occurs in couples called binary systems, and their strong gravity means they can get the matter out of their companions.

One such system has been identified by NASA's X-Ray Chandra Monitoring Project, which uncovered unusual X-rays coming from the dual system containing a white dwarf called ASASSN-16oh. Typically, the star is expected to produce low-energy x-rays called soft X-rays. But the white dwarf of ASASSN-16oh emits X-rays that are much brighter than expected, making it an unusual classification as a source of "supersonic" X-rays.

Supernatural X-rays suggest that the white dwarf must have a temperature of several hundred thousand degrees, which is warmer than normal stars. This high temperature, however, is only at certain points on the surface of the star. Astronomers believe this may be due to the fact that ASASSN-16oh extracts material from its companion red giant at a rapid pace, and this question becomes hotter and hotter when it turns to the white dwarf. The hot gas accumulates on the accretion disc (a disc of matter spinning around the star), where it eventually merges with the surface of the star and produces x-rays. However, as this process occurs at different speeds, there are several instances when the material flows faster and the star temporarily produces brighter x-rays.

Chandra white dwarf supersoft xray
Illustration of a white dwarf who draws fabric from a red giant. NASA

Previously, it was believed that the X-ray rays of supersoft were observed only when nuclear fusion occurred in white dwarfs. But in the case of ASASSN-16oh, the uneven X-ray distribution in addition to the optical light given too weak indicates that synthesis does not happen in this star. "Our result is contradictory to the long-standing consensus on how a white dwarf X-ray emission is produced," said Thomas Nelson of the University of Pittsburgh before NASA. "We now know that X-ray radiation can be done in two different ways: nuclear fusion or cloud cover."

Source link