Astronomers discover a new type of star covered in helium burning ashes


Date:
February 14, 2022
Source:
Royal Astronomical Society
Summary:
Astronomers 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.



FULL STORY ==========================================================================
A team of German astronomers, led by Professor Klaus Werner of the
University of Tu"bingen, 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.

"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.

========================================================================== Story Source: Materials provided by Royal_Astronomical_Society. Note:
Content may be edited for style and length.


========================================================================== Related Multimedia:
* Artist's_impression_of_a_rare_kind_of_stellar_merger ========================================================================== Journal Reference:
1. Klaus Werner, Nicole Reindl, Stephan Geier, Max
Pritzkuleit. Discovery of
hot subdwarfs covered with helium-burning ash. Monthly Notices of
the Royal Astronomical Society: Letters, 2022; 511 (1): L66 DOI:
10.1093/ mnrasl/slac005 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220214183335.htm

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