A peculiar type of ultraheavy star, known as a ‘barium star,’ has been found to grow massive by consuming the bloated, dying remains of its companion star. While astronomers have long suspected these stars, named for their high levels of barium, are fueled by material from a companion, new research provides the first concrete evidence of these stellar leeches in action.
Astronomers first discovered these stars in 1951, noting the unusually high levels of barium in their atmospheres. Stars are primarily composed of hydrogen and helium, but they contain trace amounts of heavier elements, like barium. Barium stars, however, stand out. They contain large quantities of various heavy elements, formed through a specific process called the s-process.
Astrophysicists already understood that the s-process occurs within large stars nearing the end of their lives. During this process, neutrons collide with light elements like helium and hydrogen, triggering them to fuse into heavier elements like carbon, strontium, and barium. However, barium stars are not always near the end of their own lives, suggesting they couldn’t have formed these heavy elements themselves.
In a recent study published on the preprint database arXiv, astronomers confirm that these peculiar stars are indeed cosmic leeches. They discovered two new barium stars, carefully analyzing their composition and ruling out other potential processes that could have led to their unique makeup. Importantly, they confirmed that both stars are part of binary systems, with one companion being a white dwarf – the remnants of a sun-like star.
Since barium stars cannot create their heavy elements independently, nearby companion stars are the most likely source. This scenario involves the companion star going through its entire life cycle. As the companion star nears the end of its life, it undergoes the s-process, producing copious amounts of barium and other heavy elements. These elements then accumulate in the star’s upper atmosphere. Eventually, the companion star swells into a red giant and sheds its atmosphere, some of which is transferred to its partner. This transfer enriches the partner star, transforming it into a barium star.
While astronomers long suspected this scenario, they lacked direct proof. The newly discovered binary barium stars provide compelling evidence for this complex process, adding another fascinating chapter to our understanding of stellar evolution and the creation of heavy elements in the universe.
