Warwick Astronomers Find Evidence of Stellar Merger in White Dwarf.

Research conducted by Dr Snehalata Sahu, Research Fellow at the University of Warwick, and colleagues has provided compelling evidence that WD 0525+526, an ultra-massive white dwarf located 130 light-years distant, originated from the merger of two stars. Utilising ultraviolet spectroscopic observations from the Hubble Space Telescope, the team detected trace amounts of carbon rising from the core of WD 0525+526 – a white dwarf possessing a mass 20% greater than that of the Sun – into its hydrogen-rich atmosphere. This detection is significant as the presence of carbon signatures, invisible to optical telescopes, indicates an origin inconsistent with the collapse of a single massive star, a previously considered formation pathway for such high-mass white dwarfs. Published in Nature Astronomy, the findings suggest that a substantial population of merger remnants may currently be misclassified as standard, pure-hydrogen atmosphere white dwarfs, highlighting the necessity of dedicated ultraviolet surveys for accurate stellar population characterisation.

White Dwarf Origins

Astronomers at the University of Warwick, led by Research Fellow Dr Snehalata Sahu, have presented compelling evidence supporting a novel origin story for ultra-massive white dwarfs – specifically, their formation through stellar mergers. Published in Nature Astronomy, the research details observations of WD 0525+526, a white dwarf located 130 light-years from Earth, possessing a mass approximately 1. 2 times that of the Sun. This finding challenges conventional models suggesting such massive white dwarfs formed from the single evolution of a massive star, providing a crucial distinction. The research team employed detailed modelling of convective processes and atmospheric diffusion to validate this interpretation of the observed spectral data.

White dwarfs represent the final evolutionary stage for approximately 97% of stars and typically possess around half the mass of our Sun compressed into a volume comparable to that of Earth. Their composition primarily consists of carbon and oxygen, remnants of nuclear fusion processes that ceased when the star exhausted its fuel. These massive white dwarfs are important because they can ultimately become Type Ia supernovae.