Some star systems thought to host two stellar bodies might actually have a hidden third – a treacherous star that could help push one of its glowing companions toward the other, as the latter feasts on its victim like a vampire.
It’s a discovery made by scientists from the University of Leeds who analyzed data from the European Space Agency’s (ESA) Gaia mission, which identifies the positions of a billion stars throughout the Milky Way . This revelation could transform our understanding of the evolution of the most massive stars in the cosmos.
So-called vampire stars, more formally known as “Be” stars, are typically surrounded by rings of superheated gas. They are a subcategory of B stars, extremely bright and between 2 and 16 times more massive than the sun. Yet even though Be stars were discovered about a century and a half ago, in 1866, how disks form around these massive stars remains an enigma.
So far, the main theory suggests that Be disks are created when stars rotate rapidly, causing them to rip stellar matter from their companion stars. This material removed from the victim star is also thought to carry angular momentum that further “accelerates” the rotation of the feeding stellar vampires. The team’s new research further strengthens the theory, however, suggesting that Be stars may live in three-star systems rather than double-star systems, interacting with two companion stars, not just one.
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“We looked at how stars move across the night sky, over longer periods, like 10 years, and shorter periods, around six months,” said the University’s Ph.D. from Leeds. student Jonathan Dodd said in a statement. “If a star is moving in a straight line, we know there is only one star, but if there are several, we will see a slight wobble or, in the best case, a spiral. ”
The team applied this principle to two groups of stars: B stars in general and Be stars in particular. The researchers then discovered that Be stars seemed to have a lower rate of companions than B stars. This was somewhat puzzling.
“We would expect them to have a higher rate,” Dodd said.
Vampire stars can ask star slaves to do whatever they want
Team leader René Oudmaijer, a professor at the University of Leeds, believes the lack of detection of companion stars could be because some stars become too faint to see after being feasted on by Be stars.
The team also found that the distances between companion stars in B star systems and Be star systems appear to be similar. It’s also strange, the researchers suggest, because Be stars are thought to be enveloped in a stellar cloak made of stripped materials, while B stars are not.
Together, these two components imply that there could be a third star in the Be systems pushing the feast stars closer to the Be stars, acting almost as cosmic “Renfields” (Dracula’s slave in Bram Stoker’s gothic horror novel) and providing their vampire star masters with victims on which ones to have dinner.
Once the victim companion stars get close enough to the Be stars, the mass of the former can be transferred. However, rather than falling directly onto the vampire star, the team says this material first forms a swirling disk around the victim star. So, perhaps the companions of the Be stars become victims, in line with the Be stellar disk theory, eventually becoming too small and too faint to see after being sucked in.
Beyond Be systems
The team’s findings could also have implications outside of stellar physics, perhaps teaching scientists more about how stars die to become black holes or neutron stars. They could also shed light on how the binaries in these stellar remnants themselves generate ripples in the very fabric of space-time, called gravitational waves.
“There is currently a revolution in physics around gravitational waves. We have been observing these gravitational waves for only a few years now, and it was discovered that they were due to merging black holes,” Oudmaijer explained. “We know that these enigmatic objects – black holes and neutron stars – exist, but we don’t know much about the stars that would become these objects.
“Our results provide a clue to understanding these gravitational wave sources.”
The University of Leeds researcher added that over the past decade, astronomers have increasingly discovered that existence in a binary system is an extremely important part of stellar evolution. This research could show that triple systems are just as important to consider as binary stars.
“We are now moving more towards the idea that it is even more complex than that and that we need to consider triple stars,” Oudmaijer concluded. “Indeed, triples have become the new binaries.”
The team’s research was published November 21 in the journal Monthly Notices of the Royal Astronomical Society.