Astronomers have discovered the hottest white dwarf star in the galaxy

A dying star located on the outskirts of the Milky Way is the hottest white dwarf ever found in our galaxy, boasting a record-setting temperature of 250,000 degrees Celsius despite the fact that it has already entered its cooling phase, according to a new study.

Writing in the journal Astronomy & Astrophysics, a team of astronomers from the University of Tübingen reported that analysis of ultraviolet spectra taken by the Hubble Space Telescope show that the white dwarf RX J0439.8-6809 has a temperature of a quarter of a million degrees.

Such extreme heat can only be reached by a star five times more massive than the sun, and even more remarkably, the white dwarf is already in the process of cooling down. At its peak about 1,000 years ago, RX J0439.8-6809 likely reached a maximum of 400,000 degrees.

Previously, the hottest temperature observed on a dying star was measured to be 200,000 degrees Celsius, the study authors said. For the sake of reference, our sun’s surface temperature has been a fairly constant 6,000 degrees since it was born 4.6 million years ago.

An unusual gas cloud around the star

The study authors added that they witnessed an intergalactic gas cloud moving towards the Milky Way for the first time. This, they explained, would suggest that at least some galaxies gather new materials from deep space and use those substances to manufacture new stars.

The chemical composition of RX J0439.8-6809 is not yet fully understood. The star, which was first discovered two decades ago, appears to have both carbon and oxygen on its surface. Those elements are the products of the nuclear fusion of helium, but in most cases, that process occurs deep within the core of a star, the researchers said.

The white dwarf was initially believed to have been located in the Large Magellanic Cloud, but the new Hubble data revealed that it is actually located on the very edge of the Milky Way and is travelling outwards at a speed of 220 kilometers per second. Much to the astronomers’ surprise, the ultraviolet spectrum also revealed the presence of gases that are native not to the star.

Those gases are part of a cloud between the Milky Way and RX J0439.8-6809 that is moving towards the Large Magellanic Cloud at a velocity of 150 kilometers per second. Its composition reveals that it originated from intergalactic space, the researchers explained, providing evidence that galaxies do indeed gather deep space materials that are used to create new stars.


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