European probe "stargazer" GAIA has counted the number of white dwarfs in the immediate vicinity of the Sun and found hints that a quarter of them arose from the merger of two other "dead stars", which was previously considered a relatively rare event, according to Universe Today.
“Supernovae of the first type, resulting from the merger of white dwarfs, have already helped us find out that the universe is expanding with acceleration. Despite this, we still do not know exactly where and how these flares are born, and how pairs of white dwarfs are formed. The traces of white dwarf mergers that we have discovered will help us assess how often and where they occur,”says Mukremin Kilic of the University of Oklahoma in Norman (USA).
White dwarfs are the remnants of old "burned out" stars of small mass, devoid of their own energy sources. White dwarfs appear at the final stage of the evolution of stars with a mass not exceeding the solar mass by more than 10 times. Ultimately, our star will also turn into a white dwarf.
Astrophysicists are interested in such "dead stars" for several reasons. Firstly, they are the progenitors of the first type of supernovae, which make it possible to very accurately estimate distances in space, and secondly, they consist of exotic superdense matter, the properties and structure of which scientists have not yet fully understood.
And finally, due to their very long lifespan, white dwarfs can be used as a kind of "fossils" that allow astronomers to recognize what our Galaxy or its neighbors looked like in the distant past.
For this, as noted by Kilich, you need to know one important thing - the exact distance to the white dwarfs and their total number. The first is necessary for an accurate assessment of their size and luminosity, and the second - for understanding the conditions under which they could arise.
Both of these problems can be solved by the GAIA probe, a European probe launched in 2013 specifically to determine the exact position and brightness of more than a billion stars in the Milky Way.
In April this year, the GAIA scientific team published the first preliminary data catalog containing the coordinates and descriptions of some of these luminaries. This was used by Kilich and his colleagues to estimate how many white dwarfs live in the next 300 light years from the Sun.
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As it turned out, our star is surrounded by a lot of "dead stars" - 13928 white dwarfs, some of which live in a pair with normal stars or other compact objects. Thanks to this, as noted by Kilich, the number of known "dead stars" in the vicinity of our planet has grown 30 times.
Carrying out such a "population census", astronomers noticed something unusual - it turned out that among them there were an unusually many heavy luminaries close in mass to the Sun. In addition, the number of white dwarf pairs was much lower than scientists expected.
Both, according to Kilich and his colleagues, are explained by the same thing - white dwarfs merge with each other much more often than we are used to thinking. How this happens is not yet clear, but the disclosure of the mechanism of their unification can radically change the picture of the evolution of stars and our ideas about how often supernova explosions of the first type occur.
