Astronomers found out that the main “suppliers” of carbon in the milky way is the fourth in prevalence in the Universe of element, compounds of which are the basis of life on the earth were carbon stars, in half to two times greater than the Sun. To such conclusion scientists have come, having analysed a couple of dozen white dwarfs, reported in an article in Nature Astronomy.
Life on Earth is based on a great variety of carbon compounds, but where does it come from in our galaxy is still not clear. Some research suggests that it is formed in the stellar wind of large bodies, which end their existence by the explosion of a supernova, while other observations indicate that the carbon source can be small stars (mainly carbon, whose atmosphere more carbon than oxygen) that have lost their outer shell and become a white dwarf — the remains of the hot dense cores of stars.
To find out which carbon stars are the main distributors of carbon in interstellar space, Paola Marigo (Paola Marigo) from the University of Padua together with colleagues analyzed 19 white dwarfs from older star clusters half a billion years. White dwarfs are one of the final stages of stars: once a star turns into a red giant (the Sun is about five billion years), it swells, discards the outer shell and its inner core, on the contrary, is compressed, forming a white dwarf. The scientists analyzed the ratio of the mass of the “ancestor” of the white dwarf and the final mass of the resulting object: it can give information about how much gas is enriched with metals (in astronomy metals — elements heavier than hydrogen and helium) were released into the interstellar medium.
As a rule, the larger the initial mass of the star, the more mass a white dwarf. However, white dwarfs were much heavier than predicted by models that take into account their original size. In particular, the jump was observed among the objects, the mass of the progenitors of which surpassed the sun 1.65–2 times. According to the authors, this anomaly can be followed by a slow evolution of carbon stars.
In the classical carbon stars, the abundance of the eponymous element is considered to be the result of helium burning during the triple alpha process within a star. The fusion products are moved to the surface of the star episodic convection. Astronomers think the helium flash, which will start burning helium in the triple alpha process, in the case of “ancestors” suddenly a large white dwarfs inherently bad reached the deep layers of the star. As a result, carbon is transferred from the subsoil to the outer shell very slowly, and stellar wind, the cause of which is the pressure of radiation in spectral lines of heavy elements such as carbon or nitrogen, has also proved to be weak. This extended the life of the carbon stars and gave them to nuclei more time to grow.
More active “suppliers” of carbon in the young milky way could be stars that are twice the size of the Sun (although the smaller body still played an important role). The content of carbon in the shell was supposed to be higher, and the stellar wind is stronger. The researchers also showed that the stars with mass less than 1.5 solar did not contribute to the diffusion of carbon in the interstellar medium.
Earlier we told you that astronomers have found the closest to Earth the double white dwarf of extremely low mass. It is assumed that a few dozen billion years it will merge components that may lead to the supernova.