Astronomers have discovered a star with an atmosphere of pure oxygen

Astronomers have discovered a star with an atmosphere of pure oxygen
Astronomers have discovered a star with an atmosphere of pure oxygen
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Until now, the existence of such stars has been predicted only by a few theories. Medium in size, but very ancient, these stars have used or lost light elements from their atmospheres, so that their outer layers contain only oxygen.

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It is known that when a not too large (up to 10 solar masses) star evolves, it discards its outer shells and remains a dim and dense white dwarf. Heavy elements move closer and closer to the center over time, while light elements - primarily hydrogen and helium - rise to the surface. This is a very common process: in fact, apart from 3% of the largest stars, the rest end their lives in the form of white dwarfs, the size of which is usually only several times the size of the Earth, and the mass is several times smaller than the Sun.

However, the white dwarf SDSS J124043.01 + 671034.68, discovered by German and Brazilian astronomers, did not develop according to the classical scenario. It was possible to notice the star (which the authors call Dox for short) among the data on more than 4.5 million stars collected over 15 years of the Sloan Digital Sky Survey (SDSS).

Studying these data, Professor Souza Kepler and his colleagues discovered a white dwarf with a very exotic atmosphere, 99.99% oxygen and containing only small impurities of neon, magnesium and silicon. Until now, no one has seen such a thing: the upper layers of the dwarf do not contain either the most common hydrogen in the Universe, or completely ordinary helium.

The reasons for this are not fully understood, but it is assumed that time is the culprit. Over the years, light elements can simply evaporate from the atmosphere of the white dwarf into space, and if Dox is extremely old, then on it this process could reach the final stage. But what about other, heavier elements that are present in the atmospheres of tens of thousands of white dwarfs studied to date? Susa Kepler and his colleagues speculate that the second star with which Dox once formed a binary system may be the culprit for their disappearance. It could pull over some of the outer shells of the white dwarf, exposing layers of pure oxygen.

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