Overview

• Hubble’s ultraviolet spectrograph uncovered trace carbon in WD 0525+526’s atmosphere that was invisible in optical observations.
• The white dwarf’s hydrogen-helium envelope is measured to be 10 billion times thinner than in typical counterparts, consistent with merger stripping.
• Surface carbon abundance is about 100,000 times lower than in other merger remnants, indicating WD 0525+526 occupies an earlier post-merger stage.
• Researchers identified semiconvection as the mixing mechanism allowing carbon to rise into the star’s hot atmosphere.
• Scientists say many merger remnants may masquerade as ordinary white dwarfs and urge future space-based ultraviolet telescopes to expose them.