A team of astronomers has discovered a unique new object that defies categorization and sheds light on the mysteries of white dwarfs. The object, named WD 0525+526, is an ultra-massive white dwarf with an outer layer of hydrogen and helium, making it 10 billion times thinner than expected.
White dwarfs are the remnants of stars like our Sun or those slightly more massive, which have exhausted their fuel and expanded into red giants before shedding their outer layers. The remaining core contracts to form a dense, hot white dwarf. Most white dwarfs have about 60% of the mass of our Sun and cool over time due to the lack of internal heat sources.
However, recent observations from the Gaia spacecraft revealed the existence of “hot” and “old” white dwarfs, which gain heat through the crystallization process caused by their extreme density. Six such massive white dwarfs were studied, with evidence suggesting they formed through merger events. WD 0525+526 differs from these examples, lacking carbon features typically seen in optical observations.
The Hubble Telescope played a crucial role in detecting the presence of carbon and confirming the object’s origin from a merger event. Researchers believe that the white dwarf is not undergoing full convection, which would allow carbon to escape, but instead has a semi-convection process below a thin layer of hydrogen.
“This discovery is puzzling, and we can’t explain it with other scenarios,” said Dr. Snehalata Sahu, co-lead author from the University of Warwick. “The hydrogen and helium layer is incredibly thin, indicating that some process must have stripped away excess hydrogen and helium.”
The team’s findings highlight the importance of ultraviolet observations in revealing hidden features of white dwarfs. The Hubble Telescope will soon be replaced by the Ultraviolet Explorer, but researchers stress that there is currently no other telescope capable of performing this type of work.
“We can’t afford to wait; we need to plan for the next generation of UV telescopes,” Dr. Sahu added.
The study, published in Nature Astronomy, contributes to our understanding of white dwarf binaries and the pathways leading to supernova explosions. The team plans to explore how common carbon white dwarfs are among similar objects and investigate stellar mergers hiding within the “normal” white dwarf population.
Source: https://www.iflscience.com/unique-white-dwarf-heavier-than-the-sun-is-hiding-a-merger-in-its-past-80450