This Is the Hottest White Dwarf in Our Galaxy

White dwarf Sirius B
This is a photo of nearby white dwarf Sirius B. No, not the big star at center -- the little faint one just to the bottom-left. (Image credit: NASA, ESA, H. Bond (STSCI), AND M. Barstow (University of Leicester))

New observations of a white dwarf reveal that it is a scorcher, at roughly 250,000 degrees Celsius (482,000 Fahrenheit) -- about 2.5 times hotter than a typical star remnant that is just beginning to cool. What's more, scientists discovered the dwarf lives just at the edge of the Milky Way, contradicting previous research showing it is from outside the galaxy.

ANALYSIS: Kepler Watches White Dwarf Warp Spacetime

The new observations come courtesy of ultraviolet observations performed by the Hubble Space Telescope, suggesting that the star was once five times more massive than our own Sun. No one is quite sure how this star got so hot, and its chemical composition still needs to be analyzed.

"The strange thing about this white dwarf (and its cooler twin H1504+65) is the surface composition," wrote lead author Klaus Werner of the University of Tübingen in Germany, in an e-mail to Discovery News. "It is carbon and oxygen without hydrogen and helium. Currently, there is no good explanation for this phenomenon. Commonly, white dwarfs have either hydrogen-dominated or helium-dominated atmospheres."

ANALYSIS: Could Dead Stars Support Life?

A little bit is known about RX J0439.8-6809 by modelling its history. It appears the star's temperature peaked at more than 400,000 degrees Celsius about 1,000 years ago. It was spotted in X-ray images about 20 years ago because it was so hot, but it originally was believed to be in the Large Magellanic Cloud, a galaxy outside of our own.

"Future X-ray surveys (eRosita) combined with optical surveys might reveal more of this kind of white dwarf with unusual surface composition," Werner added. "The search for trace elements (other metals) might give hints as to the evolutionary history."

The research was recently published in the journal Astronomy and Astrophysics.

Originally published on Discovery News.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at:

Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: