Beryllium signal identifies stars that have swallowed rocky planets

An international team led by researchers from the University of São Paulo (USP) in Brazil has developed a method to identify stars that have consumed rocky planets. The technique detects variations in the abundance of beryllium, a rare element, and could provide new insights into planetary system evolution. The study, published in Astronomy & Astrophysics, analyzed a binary system of two similar solar-type stars, HD 129171 and HD 129209. The researchers found significant differences in beryllium abundance between the two stars. HD 129171 is enriched in refractory elements, including iron, magnesium, silicon, calcium, and titanium, compared to its companion. This suggests that HD 129171 has engulfed planetary material throughout its evolution. The study is unique because it demonstrates that differences in beryllium abundance in binary stars can reliably indicate planetary engulfment. Beryllium is not produced in stellar cores and is a warning sign when detected in a star's light, indicating it swallowed rocky material. The team used data from the UVES spectrograph on the European Southern Observatory's Very Large Telescope in Chile. The observations revealed that HD 129171 has a notably higher concentration of refractory elements and an excess of both lithium and beryllium. The researchers estimate that the material may have come from a single large planet or several smaller bodies. The study's main contribution was the chemical analysis, allowing the identification of beryllium as a marker of planetary engulfment. The authors also discussed the dynamical mechanisms causing planets to fall into their host stars, including gravitational interactions, perturbations from companion stars, and orbital migration. The study implies that stable planetary systems like the solar system may be rare. The findings support the planetary ingestion hypothesis and have implications for theories of star formation and chemical tagging. The study included researchers from USP, the Polish Academy of Sciences, the Chinese Academy of Sciences, Monash University, and Italian observatories.

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