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Binary stars are systems containing two stars that orbit each other due to their mutual gravitational attraction. There is a range of different varieties of binary stars. A new study by researchers from Lund University, among others, studied binary stars made up partly of a normal star like our own Sun and partly of a specific type of dwarf stars known as type B skins they are small bright blue celestial bodies in danger of extinction. They are remains of dying red giants that have lost their outer layer of gas.
These types of binary star systems work extremely well as a type of research laboratory to investigate how stars interact with each other. For example, previous studies of binary stars have provided answers to how red giants lose their enormous mass of gas and transform into dwarf stars. The explanation for this process is not simply that the gas burns; the gravitational pull of the other star also contributes by drawing some of the gas towards it – a form of galactic cannibalism.
But there are other questions that researchers are interested in investigating with the help of binary star systems. The current study examined bewildering aspects of the orbits of binary stars around each other. Some binary stars have orbits of a few hours, while others take several years to circle each other just once. Researchers now note that the different orbits of binary stars can be explained by the evolution of elements in the Milky Way’s past.
“Our study shows that orbits are directly related to the chemical history of our Galaxy,” says Alexey Bobrick, PhD student in astronomy at Lund University.
At the dawn of the Milky Way there were not many metallic elements, which means that the first stars had a very low iron content. In contrast, the new stars that formed later in the Galaxy’s development had significantly higher iron content. The difference in the amount of iron means that newer stars get up to 30 percent larger, so their orbits become longer as a result, ”Bobrick notes.
The study is the first to link the two main fields of research investigating the history of the Milky Way with observations and computer modeling of binary stars. The results give a clear picture of how blue subdwarf stars form. These efforts are also producing new insights into the history of the Galaxy, a research field actively studied in Lund. The current study could also be useful in the future when looking at other types of binary star systems, such as those containing stars that risk ending their lives in a giant supernova explosion.
Publication in Astronomy and Astrophysics: The observed binary populations reflect galactic history
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