The stars that swallow other stars under Alma’s gaze

The majority of stars in the Milky Way are double stars and mostly also they are red dwarfs long life. However, there are cases of triple and even quintuple systems. Better, we know the example ofAlcor and Mizar which form a triply binary system. The formation of these multiple systems is explained from the fragmentation of a single cloud molecular and dusty gravitationally collapsing. We thus obtain an open cluster of young stars, some of which are more massive than the Sun and will evolve rapidly in just a few million years to give neutron stars or some black holes.

We have reason to think that our Sun itself was part of a dual system weakly gravitationally bound like others observed today. So he would have a brother twinor a twin sister, somewhere in the Milky Way in addition to other scattered siblings for billions of years, once also scattered the open cluster of hundreds of stars where these stars were born.

Stellar evolution can cause the most massive star in a binary system to begin to swell until it overflows what is called the Roche lobe, named after the mathematician and astronomer French who took care of these questions. The tidal forces of its companion star will therefore attract matter of this star by accreting it. If the companion star is a neutron star or a black hole, we will have a source of X-rays.

Labs to understand the evolution of common-envelope binaries

A variant of the contact bits are the common envelope bits. There is now only one envelope of gas for the two stars, an envelope that goes beyond their Roche lobes. An international team of astronomers, led by members of the Chalmers University of Technology (CUT) in Sweden, recently studied this kind of binary with the network of radio telescopes Alma in Chile, as stated in an article published on this subject in the famous newspaper Nature Astronomy.

The researchers explain that: one of the most misunderstood stellar evolutionary pathways is that of the binary systems in evolution with a common envelope, when the envelope of a giant star engulfs theorbit of a companion. The ensuing interaction leads to a wide variety of systems astrophysics and associated phenomena, but occurs on a very short time scale “.

This situation is changing thanks to Alma’s observations of 15 stars in the Milky Way that had caught the attention of researchers because they emitted intense radiation associated with the spectral signature of molecules of water, to the point that these stars themselves had been nicknamed “water fountains”.

” We were very curious about these stars because they seemed to be blowing masses of dust and gas out into space, some in the form of jets with gears going up to 1.8 million kilometers per hour. We thought we might find clues to how the jets were produced, but instead we found so much more. “, explains in a press release from the CUT theastrophysicist Theo Khouri, first author of the published article.

Astrophysicists have focused in particular on the spectral signatures of molecules of carbon monoxide (CO) possessing isotopes carbon andoxygen different. We have known for a long time, and it is particularly simple to demonstrate theoretically with the equations of the Quantum mechanics in the case ofatom ofhydrogen and of these isotopes (including deuterium), that these signatures are not the same.

The astrophysicists linked these measurements in particular with the oxygen isotopes to the nature of the stars observed which all turned out to be double stars but each star was losing its outer layers very quickly so that they each had ejected about 50% of their mass in a few hundred years when they initially had about one to a few solar masses each.

The scenario invoked to explain these observations is that these stars were still very recently, during the previous few hundred years, in a state where they had a common envelope. We now have a laboratory to study the effects of the phase of stellar evolution where the layers of a star envelop another star.

This is particularly interesting since this process must take place in the resolution puzzles concerning the explosions of supernovae (one can think of objects from Thorne-Żytkow), but also according to the researchers with the events leading to collisions of black holes, to the planetary nebulae stars at the end of their lives, and including in the future of the Solar system when our Sun will turn into a red giantswallowing Mercury, Venus and possibly Earth.