NASA's Hubble Uncovers Rare White Dwarf Merger Remnant

August 13, 2025 10:00AM (EDT)Release ID: 2025-020
An illustration of a white dwarf star merging with a red giant star. The red giant is an arch across the bottom of the illustration, with a textured surface. The white dwarf is a white pinpoint object at upper center right. The white dwarf in embedded inside a teardrop-shaped cocoon of white gas. It is enveloped in a white open ellipsoid that is the bow shock from speeding through the red giant’s outer atmosphere. The words “artist’s concept” are at lower left.

Summary

Forensic evidence comes from dwarf’s unusual spectrum

Astronomers using the Hubble Space Telescope have found forensic evidence, in unique ultraviolet spectral "fingerprints," that a red giant star is merging with a white dwarf companion star. The clue is that the dwarf — a burned-out cinder of a collapsed Sun-like star — has had its outer hydrogen and helium layers stripped down, exposing subsurface carbon. This showed up in the spectrum of the white dwarf. Also, the white dwarf is rare in that it is slightly more massive than our Sun, which is uncommon for dwarfs. Most dwarfs are a fraction our Sun’s mass. This doomed, more massive dwarf is hotter than most other white dwarfs.

Our Sun will run out of fuel and collapse down to a white dwarf in roughly 5 billion years. But there’s nothing lurking out there that will eat it.

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