Artist’s impression of a uncommon type of stellar merger occasion between two white dwarf stars. Credit: Nicole Reindl
A staff of German astronomers, led by Professor Klaus Werner of the University of Tübingen, has found an odd new kind of star coated within the by-product of helium burning. It is feasible that the celebs might need been fashioned by a uncommon stellar merger occasion. The fascinating outcomes are revealed in Monthly Notices of the Royal Astronomical Society.
While regular stars have surfaces composed of hydrogen and helium, the celebs found by Werner and his colleagues have their surfaces coated with carbon and oxygen, the ashes of helium burning – an unique composition for a star. The state of affairs turns into extra puzzling as the brand new stars have temperatures and radii that point out they’re nonetheless burning helium of their cores – a property sometimes seen in additional developed stars than these noticed by Werner and his staff on this research.
Published alongside the work of Professor Werner and his staff, a second paper from a bunch of astronomers from the University of La Plata and the Max Planck Institute for Astrophysics presents a doable rationalization for his or her formation. “We consider the celebs found by our German colleagues might need fashioned in a really uncommon type of stellar merger occasion between two white dwarf stars,” says Dr. Miller Bertolami of the Institute for Astrophysics of La Plata, lead author of the second paper. White dwarfs are the remnants of larger stars that have exhausted their nuclear fuel, and are typically very small and dense.
Stellar mergers are known to happen between white dwarfs in close binary systems due to the shrinking of the orbit caused by the emission of gravitational waves. “Usually, white dwarf mergers do not lead to the formation of stars enriched in carbon and oxygen,” explains Miller Bertolami, “but we believe that, for binary systems formed with very specific masses, a carbon- and oxygen-rich white dwarf might be disrupted and end up on top of a helium-rich one, leading to the formation of these stars.”
Yet no current stellar evolutionary models can fully explain the newly discovered stars. The team needs refined models in order to assess whether these mergers can actually happen. These models could not only help the team to better understand these stars, but could also provide a deeper insight into the late evolution of binary systems and how their stars exchange mass as they evolve. Until astronomers develop more refined models for the evolution of binary stars, the origin of the helium covered stars will be up for debate.
“Normally we expect stars with these surface compositions to have already finished burning helium in their cores, and to be on their way to becoming white dwarfs. These new stars are a severe challenge to our understanding of stellar evolution,” explains Professor Werner.
Reference: ” Discovery of hot subdwarfs covered with helium-burning ash” by Klaus Werner, Nicole Reindl, Stephan Geier and Max Pritzkuleit, 12 February 2022, Monthly Notices of the Royal Astronomical Society: Letters.
DOI: 10.1093/mnrasl/slac005
