University of São Paulo: Presence of metals indicates that stars “swallow” nearby planets, astronomers reveal

In a group of more than 100 pairs of Sun-like stars, one of the stars “swallowed” planets orbiting around it in a quarter of the pairs, possibly early in its life cycle, billions of years ago. The revelation is made in an international study with the participation of the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG) at USP. Analyzing images taken by the European Southern Observatory (ESO) in Chile, astronomers discovered, in these stars, most located more than 100 light-years from our solar system, chemical elements typical of rocky, Earth-like planets such as iron and lithium. According to the researchers, our Sun does not have relevant amounts of these elements, indicating that it has engulfed few planets, possibly due to the more stable architecture of the solar system,

Details of the work are described in an article published on the Nature Astronomy website on August 30th. “The objective of the research was to look for possible signatures of the engulfment of planets by their stars”, points out Professor Jorge Melendez, from the IAG, one of the authors of the article. “Due to the gravitational interaction between the planets and the central star, they can end up ‘swallowed’ by their central stars, especially in the early stages of planetary system formation, when the orbits are more chaotic.”

“For more evolved planetary systems, whose formation is older, the phenomenon can also happen if the planet migrated to a more internal region and ended up falling on the central star”, describes the professor, “or due to a gravitational perturbation of some star that passed in the vicinity of the planetary system, which could eventually result in the planet being ejected out of the system, or being engulfed by its star”.


Altogether, about 200 stars were analyzed, which form part of more than 100 binary systems (pairs of stars). K), similar to our Sun”, explains Melendez. “The spectroscopy technique was used, using observations taken from the 3.6-meter telescope at ESO’s La Silla Observatory in Chile, to determine the chemical composition of stars.”


According to the IAG professor, the researchers selected stars that are relatively similar in binary systems. “In this way, it is possible to achieve greater precision in determining the chemical composition”, he points out. “The analysis showed that in 25% of binary systems, one of the stars had the signatures of having swallowed planetary material, such as, for example, a higher content of iron and lithium. This means that at least 25% of solar-type stars ‘devour’ their planets”.

According to Melendez, it is not known when the planets were “swallowed”, but it is more likely that this happened in the “infancy” of these systems, billions of years ago. “At that time, the orbits were very chaotic, which may have favored the migration of giant planets from the outer region to the inner region, disturbing the inner rocky planets (or protoplanets),”, he explains.

“It is interesting that the Sun has the opposite effect to that observed in anomalous stars in binary systems. Instead of observing a greater quantity of elements characteristic of rocky planets, we observed that the Sun does not have an excess of these chemical elements”, highlights Melendez. “This means that possibly the Sun has not swallowed a significant number of planets, and that perhaps the architecture of the solar system is relatively stable. This stability over long time scales may have favored the development of the most complex life on our planet.”

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