Pairs with young star and dead star in star clusters

Most stars exist in binary systems. In fact, almost half of stars similar to our Sun have at least one companion star. These paired stars usually differ in size, with one star often being significantly more massive than the other. Although these stars might be thought to evolve at the same rate, the more massive ones tend to have significantly shorter lives and go through the stages of stellar evolution much faster than their lower-mass companions.

In the red giant stage, which a star experiences when it begins to approach the end of its life, the star expands to hundreds or thousands of times its original size. In binary systems with close separation between the stars, this expansion is so dramatic that the outer layers of the dying star can sometimes completely engulf its companion. This situation is called the “common envelope phase”, since both stars are enveloped in the same material.

The common envelope phase remains one of the greatest mysteries of astrophysics. Scientists have struggled to understand how sharing an envelope during this critical period affects the subsequent evolution of stars. New research could solve this puzzle.

When stars with a not too great mass complete their red giant phase, they contract again, this time to a diameter much smaller than what they had before they were red giants. As they still retain a lot of heat, they begin to shine an intense white color. Because of these features, they are called “white dwarfs.” In any case, stars in this phase of their evolution no longer experience the nuclear reactions that keep stars active and therefore can be considered dead.

Finding binary systems in which there is a still active and young star at a short distance from a white dwarf, and both shared an outer envelope when the dead one was still alive as a red giant, is a magnificent opportunity to investigate this extreme phase of shared envelope.

And this is precisely what has been done in the new study, identifying pairs with a young star (which has not yet become a red giant) and a dead star (which is already a white dwarf) in star clusters.

This image captured by the ALMA observatory shows the star system HD101584 and the complex mass of gas around the two stars. At this stage of their common history, the couple shares the same external envelope. (Photo: ALMA (ESO / NAOJ / NRAO) / Olofsson et al. / Robert Cumming)

The study was carried out by an international team led by Steffani M. Grondin, from the University of Toronto in Canada.

With the help of an artificial intelligence system, the study’s authors reviewed data from three major sources: the European Space Agency’s (ESA) Gaia space telescope, which has observed more than a billion stars in our galaxy, as well as the 2MASS and Pan-STARRS1 cosmic surveys, which have also scrutinized the sky in depth. In their study, Grondin and his colleagues have discovered many more binary systems of the aforementioned class in young star clusters than previously known. Although these types of binary systems should be very common, they have been difficult to find, with only two candidates confirmed within clusters before this research. The new study may increase that number to 52 binaries in 38 star clusters.

Now it will be possible to begin to reveal what exactly happens between the earliest stage and the final stage of binary star systems. This, in turn, can provide new and revealing data about how stars form, how galaxies evolve and how most of the chemical elements of the periodic table were created. To find out these details about stellar evolution, the fact that almost all the stars in each of these clusters were formed at the same time or with very little difference will be decisive, which allows comparing different evolutions in the same time and space frame. .

The information collected in the new study could also help explain some supernova explosions, since binaries containing one or more of these compact dead stars are believed to be the origin of such phenomena.

The study is titled “The First Catalog of Candidate White Dwarf–Main-sequence Binaries in Open Star Clusters: A New Window into Common Envelope Evolution.” And it has been published in the academic journal The Astrophysical Journal. (Fountain: NCYT by Amazings)