Nature Paper Press Release - Prof Bertram Bitsch & Collaborators

20 Mar 2024

Diets of the stars: differences in ‘twin’ stars may be due to ingesting planets, study finds

• Groundbreaking study finds differences in co-moving stars thought to be identical
• Compositional analysis shows differences may be explained by stars ingesting entire planets
• Research conducted by UCC astrophysicist and international team from Australia, Germany, Hungary, and the US

A groundbreaking study by an international team of astrophysicists has uncovered a stunning cosmic phenomenon – co-moving stars thought to be identical to their “twins” have differences. These differences might have occurred already during their birth when the stars accrete material from their surrounding discs, but it seems more likely that one star of the pair ingested planets, challenging our understanding of planetary systems.

The study, published in prestigious academic journal Nature, delves into the findings derived from data collected with the 6.5-meter Magellan Telescopes in Chile and the W. M. Keck Observatory.  The data was also collected from the European Southern Observatory’s Very Large Telescope. The research sheds light on a celestial phenomenon where binary co-moving stars, once thought to be identical twins due to their shared molecular origins, show subtle compositional differences, hinting at the absorption of planets.

Stars can ingest planets when gravitational interactions with other celestial bodies cause the planets to be pulled into the star's vicinity. The star's gravitational forces then lead to the ingestion of the planets, influencing the star's composition.

Bertram Bitsch, Professor of Astrophysics, School of Physics at the College of Science, Engineering and Food Science at University College Cork (UCC) in Ireland, is co-author of the paper along with colleagues based in Australia, Germany, Hungary, and the United States.

Explaining their findings, Prof. Bitsch said:

"Co-moving stars come from the same molecular cloud, indicating that they should have the same composition, similar to identical twins. Stars consist mostly of hydrogen and helium; they also contain all other elements like iron, silicate, magnesium, oxygen, and carbon, which are the materials that form terrestrial planets like our own Earth.

However, detailed new high-precision observations of these stars have revealed small compositional differences between co-moving pairs, indicating that another effect is at play. The measured compositional differences in the different elements could be attributed to differences in their accretion history during the protoplanetary disc phase of the first few millions of years of their life, but this is unlikely considering that the star evolved for billions of years afterwards, wiping out these differences. It seems more likely that one of the components of the co-moving pair ingested planets, giving important constraints on the stability of planetary systems around stars”.

The study provides new evidence of planet signatures and facilitates a deeper understanding of the star-planet-chemistry connection by providing new observational constraints on the mechanisms of planet engulfment, formation, and evolution.

The research, focused on 91 pairs of stars with a shared origin and a well-defined selection function, identified at least seven instances of planetary ingestion, leading to an occurrence rate of 8%. This discovery challenges previous assumptions about the stability of planetary systems around stars.

These results have far-reaching implications for the scenarios of planet formation and engulfment and provide new insights into the long-term evolution of planetary systems.

*photo credit: Ruben Martinez, UCC.

Nature paper link: https://www.nature.com/articles/s41586-024-07091-y