Strange, extremely bright stars surrounded by huge discs of hot gas may form as they suck the life out of another star in their systems, with the help of a hidden third star, new research shows.
Previously thought to steal mass from their stellar neighbors in a binary star system, these "Be" stars may actually form in triple star systems, with the third star pushing the second towards their "vampire" star overlord, according to the study, published in the journal Monthly Notices of the Royal Astronomical Society.
These vampire Be stars are a subset of B stars, which are between three and 20 times more massive than our sun, which is a G star. Stars are classified by their spectral characteristics, or the colors of light that they emit, which are often a result of the temperature that they burn at. B stars are generally bluer in color, and have a temperature of between17,000 and 53,000 degrees Fahrenheit.
"Be stars differ from B stars because they have a disc of gas and dust surrounding them. Their discs are produced because the Be stars rotate very rapidly and this causes material from the surface of the star to be thrown off," Jonathan Dodd, an astrophysics Ph.D. student at the University of Leeds' School of Physics and Astronomy, and the paper's co-author, told Newsweek.
These Be stars were first discovered over 100 years ago, but until now, exactly how they formed has remained a mystery.
"We initially thought that Be stars formed in double star systems, with matter being transferred from the second star to the forming Be star—this transfer of matter would cause the forming Be star to rotate more and more rapidly, eventually leading to the characteristic disc forming," Dodd said. "This matter transfer would also leave what we call a 'stripped star'—a star that's had its outer layers pulled off of it—and this would necessarily be very close to the newly formed Be star, and also very faint."
The researchers now think that the Be stars form by sucking the life out of a stellar neighbor, but that this neighbor may be a star in a triple system, being pushed closer towards the Be star by the third one. The researchers found evidence for Be stars being triple systems by analyzing data from the European Space Agency's Gaia satellite.
First, the scientists noted that it appeared that Be stars had lower rates of stellar companions than B stars, but inferred that this was because the companion had been devoured to the point that it was too faint to see. Looking at another dataset of stars further away, they saw that Be and B stars seemed to have a similar rate of companions, which implies that the Be stars had two neighbors: the one being sucked dry, and a hidden third pushing it towards its fate.
"We think that the Be stars are forming in triples because in our study we show on a statistical basis that the binarity of Be stars is different than the binarity of B stars," Dodd said. "The difference in the binarity can be explained by the presence of these 'stripped stars' because they would have to move closer to the forming Be star. This happens more often in triple systems, and we point out that most Be stars that we know have a 'stripped' companion are in fact also in triple systems."
The scientists hope that this discovery could explain several other cosmic mysteries, improving our comprehension of how the universe works.
"Besides improving our understanding of Be stars, these findings could have an impact on our understanding of things like black holes, neutron stars and gravitational wave sources, because these systems could be the precursors to those objects," Dodd said.
René Oudmaijer, co-author of the paper and an astrophysics professor at the University of Leeds, agrees, noting that this discovery may mean triple star systems have more cosmic importance than we first thought.
"Over the last decade or so, astronomers have found that binarity is an incredibly important element in stellar evolution," he said in a statement. "We are now moving more towards the idea it is even more complex than that and that triple stars need to be considered. Indeed, triples have become the new binaries."
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Jess Thomson is a Newsweek Science Reporter based in London UK. Her focus is reporting on science, technology and healthcare. ... Read more
