Sun-like stars devour planets in their orbits, study shows 08/31/2021 – science

In planetary systems that are formed by sun-like stars, but which have severe dynamic processes that lead to reconfigurations in their architecture, some planets may have been “engulfed” by the host star.

An international team of astronomers – led by Lorenzo Spina from the Istituto Nazionale di Astrofisica (INAF), Padua, Italy, and with Jorge Meléndez from the Institute of Astronomy, Geophysics and Atmospheric Sciences of the University of São Paulo (IAG-USP) – studied the chemical Composition of sun-like stars in more than a hundred binary star systems to identify signatures of planets that were eventually “swallowed”. An article on this was published today (30) in the journal Nature Astronomy.

“In a binary star system, the two stars are made of the same material and should therefore be chemically identical. However, when a planet falls inside a star, it dissolves in the outermost region of the star’s interior, called the convection zone, and can change the composition of that region, increasing the content of chemical elements called “refractory” elements, which are plentiful on rocky planets available. In the stars, whose signatures indicate the intertwining of planets, larger amounts of lithium and iron are observed compared to their twin companions in the binary star system, ”says Meléndez from the FAPESP agency.

According to the researcher, lithium is destroyed inside stars, but preserved in the material of the planets. Therefore, an unusually high proportion of this chemical element in a star can indicate that planetary material has been swallowed by it.

The study was based on observations of 31 pairs of double stars, i.e. 62 stars, which were recorded with the HARPS spectrograph in the 3.6-meter telescope at the La Silla Observatory of the European Southern Observatory (ESO). The data collected on site were supplemented by previous results that were already recorded in the specialist literature.

The La Silla Observatory is located in the Atacama Desert, in the Chilean Andes, in an extremely dry, lonely region, far away from light pollution, which has one of the darkest night skies on earth.

“This was the largest sample of similar stars in binary systems ever studied, and the results showed that at least a quarter of the Sun-like stars ‘devour’ their own planets. The finding suggests that a considerable part of the planetary systems had a very dynamic past – in contrast to our solar system, which has retained an orderly architecture, ”says Meléndez.

According to study coordinator Lorenzo Spina, “the search for planets similar to the Earth is like looking for a ‘needle in a haystack’. However, this result opens up the possibility of identifying stars with a composition similar to that of the Sun based on the abundance of certain chemical elements. ”Stars that lack so-called refractory elements tend to harbor structures that are analogous to our solar system.

A well-studied dual system are 16 Cygni, which are located about 69 light years from Earth. The system consists of two yellow sun-like dwarf stars, 16 Cygni A and 16 Cygni B. It can also contain a red dwarf star. It is estimated that 16 Cygni A and 16 Cygni B are separated by a distance of 860 AU. are separated from each other [sendo UA, a unidade astronômica, definida pela distância entre a Terra e o Sol]. For comparison purposes, the distance between the sun and the so-called heliopause, which is the outermost limit of the solar system, is estimated to be 110 to 160 AU. Despite the enormous distance between the twin stars, the highly eccentric orbit of a planet larger than Jupiter and orbiting star 16 Cygni B could be due to the gravitational perturbation of star 16 Cygni A.

“It is interesting to note that the component 16 Cygni A, which has no proven planets, is abundant in refractory elements, suggesting that this star may have already swallowed planets,” comments Meléndez.

The research was supported by FAPESP through the thematic project “High-precision spectroscopy: from the first stars to the planets” coordinated by Meléndez.

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