One of these twin stars has likely been snacking on exoplanets
Astronomers have discovered a fascinating phenomenon in the binary star system HD 81809, located a mere 101 light-years away. This system, consisting of two stars, HD 81809A and HD 81809B, has revealed a surprising twist in the cosmic dance of celestial bodies. The stars, formed from the same vast cloud of gas and dust, should theoretically share identical chemical compositions, but a recent study has uncovered a peculiar discrepancy.
The research, led by Nuno Moedas of the Technical University of Denmark, highlights a significant difference in the chemical makeup of the two stars. HD 81809B, the cannibal star, exhibits a much higher concentration of elements heavier than hydrogen and helium, known as 'metals,' at its surface compared to its sibling, HD 81809A. This disparity has sparked a captivating scientific inquiry.
Moedas and his team propose two intriguing explanations for this chemical discrepancy. Firstly, the stars might not be 'real siblings' but could have formed from different molecular clouds, each containing distinct elements. Alternatively, the more captivating scenario suggests that HD 81809B has undergone a dramatic event, consuming an exoplanet between 50 and 75 times the size of Earth. This planetary ingestion could have drastically altered the star's chemical composition.
The evidence supporting the planetary engulfment theory is compelling. The high abundance of lithium in HD 81809B, an element typically scarce in stars due to its volatility, points towards a planet's ingestion. Moedas explains that the large presence of lithium in HD 81809B can be attributed to the ingestion of a planet, as lithium is easily destroyed in stars.
The team estimates that the star has devoured planetary material equivalent to 75 times the mass of Earth, suggesting the possibility of three planets, each 25 times more massive than Earth, being consumed. Moedas acknowledges the challenges in determining the exact number of planets ingested, as physical processes within the star may have 'cleaned up' the evidence, making it difficult to reconstruct the past.
Despite these challenges, the researchers believe that a dusty disk of debris detected in the system could provide valuable insights. If located around the secondary star, this disk might be the remains of a planet falling into the star, offering a glimpse into the composition of the ingested planets. However, current instruments are not advanced enough to study this debris disk, and further observations are necessary.
This discovery not only highlights the complexity of binary star systems but also underscores the potential for exoplanetary ingestion as a significant cosmic process. As Moedas remarks, there is still much to uncover and understand about this system, leaving astronomers with a tantalizing puzzle to solve.
