Astronomers have discovered unusual stars covered with helium “ash”

(ORDO NEWS) — Astronomers believe they may have formed in a rare stellar merger.

A group of German astronomers led by Professor Klaus Werner of the University of Tübingen have discovered a strange new type of star covered in a by-product from the fusion ‘burning’ of helium.

While the surfaces of ordinary stars are made up of hydrogen and helium, the surfaces of the stars discovered by Werner and his colleagues are covered in carbon and oxygen, the “ash” of burning helium.

This is a very exotic composition for a star. But the situation becomes even more mysterious, as the temperatures and radii of new stars indicate that the helium burning reaction in their cores continues. This property is usually observed in more developed stars than those discovered by Werner and his team.

“We believe that the stars discovered by our German colleagues could have formed as a result of a very rare stellar merger of two white dwarfs.

These are the remnants of larger stars that have exhausted their nuclear fuel and are typically very small and dense,” says Miller Bertolami of the La Plata Institute of Astrophysics, who authored the second paper on this study.

It is known that the merger of white dwarfs in close binary systems occurs due to the contraction of their orbits caused by the emission of gravitational waves.

“Normally, mergers of white dwarfs do not result in the formation of stars enriched in carbon and oxygen.

But we believe that for binary systems formed with very specific masses, a carbon- and oxygen-rich white dwarf could collapse and appear on top of another, richer in helium, leading to the formation of such stars, ”- Miller Bertolami.

However, no current models of stellar evolution can fully explain these newly discovered stars. Astronomers need improved models to understand whether such mergers can actually occur.

These models should help better understand these stars and provide deeper insights into the late evolution of binary systems and how their stars exchange mass as they evolve.

Until astronomers develop more accurate models for the evolution of binary stars, the origin of stars covered in helium ash will be a matter of controversy, the authors of the study note.

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