Hot white dwarfs and pre-white dwarfs discovered with SALT

[Astronuc]

An international team of astronomers has discovered eight of the hottest stars in the universe, all with surfaces hotter than 100,000 degrees Celsius. The work was published in Monthly Notices of the Royal Astronomical Society.

The paper is based on data gathered using the Southern African Large Telescope (SALT), the largest single optical telescope in the southern hemisphere, with a 10m x 11m mirror. The study describes how a survey of helium-rich subdwarf stars led to the discovery of several very hot white dwarf and pre-white dwarf stars, the hottest of which has a surface temperature of 180,000 degrees Celsius. For comparison, the sun's surface is a mere 5,800 degrees.

https://phys.org/news/2023-01-astronomers-super-hot-stars.html

One of the stars identified is the central star of a newly discovered planetary nebula, which is one light year in diameter. Two of the others are pulsating, or "variable" stars. All of these stars are at an advanced stage of their life cycle and are approaching the end of their lives as white dwarfs. Due to their extremely high temperatures, each of these new discoveries is more than one hundred times brighter than the sun, which is considered unusual for white dwarf stars.

https://academic.oup.com/mnras/article/519/2/2321/6967306?login=false

 

[jedishrfu]

Do they know why the stars are so hot?

 

[Ken G]

White dwarfs are very hot when first liberated from the AGB star that used to surround them, since they are what is left over from the hot stellar core. So one presumes these are recently liberated and have not yet had much time to cool. If they are older, it might be that they recently merged with another white dwarf, which could heat them up again.