SCIENTINGS OF THE PLANETOLOGICAL USEX OF THE US Institute has decided the riddle associated with the formation of discs from fragments around white dwarfs. It is known that these discs appear only 10-20 million years after the stage of the Red Giant. In a new article published in The Astrophysical Journal Letters magazine, researchers explained the reason for this delay.
During the red giant phase, the star loses a significant part of its masses, before turning into a white dwarf, consisting of carbon and oxygen, the size of the ground and with a half mass of the Sun. At this time, the orbits of any remaining planets are destabilized, and the asteroids are discarded towards the white dwarf. When they approach too close, the tidal forces of the star turn them into dust. It is expected that young white dwarfs quickly form discs, but this does not happen.
It turned out that the delay is explained by the temperature of the white dwarfs. They are so hot that any dust evaporates quickly and dissipates. This evaporation is terminated only when the surface temperature of the white dwarf cools up to about 27 thousand Kelvinov. This is consistent with observation data: discs were discovered in dwarfs whose temperature is below critical.