Credit: Nicole Reindl
Licence type:Attribution (CC BY 4.0)
A team of German astronomers, led by Professor Klaus Werner of the University of Tübingen, have discovered a strange new type of star covered in the by-product of helium burning. It is possible that the stars might have been formed by a rare stellar merger event. The fascinating results are published in Monthly Notices of the Royal Astronomical Society.
While normal stars have surfaces composed of hydrogen and helium, the stars discovered by Werner and his colleagues have their surfaces covered with carbon and oxygen, the ashes of helium burning – an exotic composition for a star. The situation becomes more puzzling as the new stars have temperatures and radii that indicate they are still burning helium in their cores – a property typically seen in more evolved stars than those observed by Werner and his team in this study.
Published alongside the work of Professor Werner and his team, a second paper from a group of astronomers from the University of La Plata and the Max Planck Institute for Astrophysics offers a possible explanation for their formation. “We believe the
stars discovered by our German colleagues might have formed in a very
rare kind of stellar merger event 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 need 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.
p style="text-align: justify;">“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.
by Gurjeet Kahlon
Source: Royal Astronomical Society (RAS)/News
Media contacts
Gurjeet Kahlon
Royal Astronomical Society
Mob: +44 (0)7802 877 700
press@ras.ac.uk
Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
press@ras.ac.uk
Science Contacts
Professor Klaus Werner
Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Germany
werner@astro.uni-tuebingen.de
Dr Miller Bertolami
Institute for Astrophysics of La Plata, CONICET-National University of La Plata, Argentina
mmiller@fcaglp.unlp.edu.ar
Further Information
The
research appears in “Discovery of hot subdwarfs covered with
helium-burning ash”, K. Werner, N. Reindl, S. Geier and M. Pritzkuleit
and “An evolutionary channel for CO-rich and pulsating He-rich
subdwarfs” M. M. Miller Bertolami T.Battich, A. H. Córsico, L. G.
Althaus, F. C. Wachlin, both published in Monthly Notices of the Royal
Astronomical Society, in press. The papers can be found at https://academic.oup.com/mnrasl/article-lookup/doi/10.1093/mnrasl/slac0… andhttps://academic.oup.com/mnrasl/advance-article-abstract/doi/10.1093/mn…, respectively.
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