New research has confirmed that a type of ultraheavy star rich in the element barium grows to an enormous size by absorbing celestial material from a companion. They are called “barium stars” because of how much barium they contain.
The stars were first discovered in 1951 when astronomers William P. Bidelman and Philip Keena noticed high levels of barium in their atmospheres.
Initially, after their discovery, the stars were thought to be red giants, but their chemical signature was observed in the majority of stars in the galaxy as well.
All stars consist of hydrogen and helium, with trace amounts of heavier elements like barium. But barium stars contain a lot more barium than your average star, which has always posed a puzzle to researchers.
In addition to barium, they have copious amounts of other heavy elements. The presence of such elements is due to the s-process, which occurs inside large stars that are near the ends of their lives.
During the s-process, neutrons slam into lighter elements, such as hydrogen and helium. The impact triggers them to fuse into heavier elements, such as barium, carbon, and strontium.
However, barium stars aren’t always at the end of their lives, so they couldn’t have formed these elements by themselves. Instead, they feed off material from nearby cosmic objects.
A team of astronomers located two new barium stars in the sky. They measured the s-process elements within the stars and eliminated many theories that could explain how these stars came into existence.
They also determined that the stars were members of a binary system. They found compelling evidence that the companion the stars have been leeching off of was a white dwarf, the remnant of a sun-like star.
PiotrKaluza – stock.adobe.com – illustrative purposes only
Companion stars situated nearby are the best possible explanation for how barium stars get such high levels of barium. The barium star’s companion has to go through its entire life cycle for it to get its barium.
Toward the end of the companion’s life, it begins the s-process and produces considerable amounts of barium and other elements.
Then, these elements make their way into the companion star’s upper atmosphere. When the companion star expands to become a red giant, it gradually loses its atmosphere.
Some of the atmosphere is absorbed by neighboring stars, which makes them turn into barium stars. The transfer of elements is brief on an astronomical timeline.
For a long time, astronomers have suspected this situation, but they lacked the concrete evidence to confirm it until now. The binary barium stars are the first examples of their kind.
Now that scientists understand more about their nature, the discovery has served as a piece of the universe’s complex puzzle.
The paper was published in the preprint database arXiv.
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