Using the Gemini South telescope, a team of astronomers has discovered that differences in the composition of binary stars can originate from variations in the chemical makeup of the cloud of stellar material from which they formed. This finding challenges current stellar and planet formation models, as it explains why stars born from the same molecular cloud can have different chemical compositions and host different planetary systems. Led by Carlos Saffe, the team utilized the Gemini High Resolution Optical Spectrograph (GHOST) to study the spectra of a pair of giant stars, revealing significant differences in their chemical composition. The researchers found that one star had higher abundances of heavy elements than the other, suggesting that the variations began before the stars even started to form.
Binary star systems are common, with up to 85% of stars existing in such systems. These stellar pairs are born out of the same molecular cloud with shared chemical building blocks, leading astronomers to expect that they would have nearly identical compositions and planetary systems. However, many binaries exhibit differences in composition that cannot be explained by events occurring after the stars evolved. Previous studies have proposed three potential explanations for these differences, including atomic diffusion, planetary engulfment, and primordial areas of nonuniformity within the molecular cloud. By focusing on a binary system of two giant stars, Saffe’s team was able to eliminate two of these explanations and confirm that primordial differences within the molecular cloud are responsible for the variations.
This study has significant implications for understanding the diversity of planetary systems in binary stars. The findings explain why binary stars can host different planetary systems with varying types of planets orbiting at different distances from their host stars. The results also challenge the concept of chemical tagging, which uses the chemical composition of stars to identify those that originated from the same stellar nursery, by demonstrating that stars with different compositions can have the same origin. Additionally, the study suggests that observed differences in stars, previously attributed to planetary impacts, may actually be inherent from the beginning of a star’s life.
The team’s discovery that primordial differences in binary stars’ compositions can result from variations in the molecular cloud where they formed highlights the complexity of star and planet formation processes. By observing stars at the end of their lives, astronomers using the GHOST instrument at Gemini South are gaining insights into the conditions in which stars are born and how these conditions influence their entire existence over millions or billions of years. This research offers a new perspective on how the early stages of star formation can shape the evolution of stars and their planetary systems, adding to our understanding of the diverse nature of the universe and the complexities of stellar and planetary formations.
