Contracting white dwarf noticed for the primary time


Astrophysicists from MSU (Russia) and his colleagues from Italy and Russian Academy of Sciences have discovered the primary observational proof for a contracting white dwarf. Constant excessive spin-up fee of a star of this kind, situated in an enigmatic binary system, might be simply defined if the white dwarf is contracting, the researchers argue. The discovery is reported within the Monthly Notices of the Royal Astronomical Society.

“Thanks to this discovery, astrophysicists will be able to study and evaluate the evolution patterns of young white dwarfs – and successfully look for similar systems in the galaxy, ” – famous the primary writer of the article, astrophysicist Sergei Popov (SAI MSU).

It is extensively believed, primarily based on theoretical issues, that younger white dwarfs – the compact remnants of solar-like stars, – ought to expertise a section of contraction of their adolescence. The radius of a typical white dwarf can lower by a number of hundred kilometers through the first million years of its life.

However, there was no observational proof for this impact thus far. First, as a result of a lot of the identified white dwarf are a lot older. Second, as a result of the scientists shouldn’t have a direct and exact technique to measure the radii, and their variations, in these stars.

Studying an enigmatic X-ray supply in a binary system of a uncommon kind, the scientists might need discovered the primary observational proof for a contracting white dwarf. The binary system HD49798/RX J0648.Zero-4418 is at a distance of 2000 gentle years, within the Puppis constellation, and has been extensively studied with optical, UV, and X-ray telescopes.

It comprises a large white dwarf, which spins with a interval of solely 13 s, the quickest identified for a white dwarf, and emits X-rays as a result of accretion of matter captured from the stellar wind of its companion star.

Sandro Mereghetti (a coauthor of the brand new paper) lately found that the rotational velocity of this white dwarf has been steadily rising through the newest 20 years. Its spin interval of 13 s is reducing by 7 nanoseconds yearly.

This might sound a really small change, however it’s truly a really giant impact for a physique weighting greater than our Sun, however with a radius as small as about 5000 km (lower than the Earth). Indeed, such a big spin-up fee couldn’t be simply defined in commonplace methods (e.g. by the captured angular momentum of the accreting matter).

The resolution to this puzzle has been now introduced by the authors of this new examine. They display that the excessive spin-up fee might be simply defined if the white dwarf is contracting, precisely as within the case of a spinning skater that brings in her arms to rotate quicker.

The evolutionary calculations introduced within the paper present that the white dwarf has an age of solely about 2 million years. The contraction fee of about one centimeter per 12 months anticipated for this age is strictly of the correct quantity to clarify the measured spin-up fee, exhibiting that that is the primary instance of contracting white dwarf ever recognized.

“For decades it has been theoretically clear that that young white dwarfs are contracting. Yet, that very phase of contraction has never been observed “in actual time”. We ought to thank the individuality of the binary system underneath examine: the white dwarf was actually illuminated (as a result of accretion of matter from the neighboring star).

But it was highlighted so neatly that the accreting matter didn’t have an effect on its rotation – an especially uncommon phenomenon! In different comparable methods, accretion is far more highly effective: it determines how the white dwarf rotates, which makes it unimaginable to note the great thing about contraction”, – Popov defined.

Research paper


The star that might not die

Goleta CA (SPX) Nov 09, 2017

Supernovae, the explosions of stars, have been noticed within the 1000’s and in all circumstances they marked the dying of a star. Astronomers at Las Cumbres Observatory have found a outstanding exception – a star that exploded a number of occasions over a interval of greater than fifty years. Their observations are difficult current theories on these cosmic catastrophes.

When the supernova, named iPTF … learn extra

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Lomonosov Moscow State University

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