'Vampire' stars could be using galactic henchmen to help feed on their companions

• Type-Be stars, nicknamed "vampire" stars, are believed to strip the mass of a nearby star.
• Scientists are trying to figure out how this happens.

Massive "vampire" stars that feast on their celestial companions could be assisted by a third, hidden star, new research in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society found.

Type-Be stars, characterized by their large size and surrounding rings of gas, are a subset of type-B stars, which are very hot, bright, and blue. The subtype makes up about 20% of the type-B star population, Jonathan Dodd, a Ph.D. student and one of the study's lead co-authors, told Business Insider.

The nickname "vampire stars" comes from the most accepted theory of how type-Be stars form rings, researchers said in the study — by sucking the metaphorical neck of an intergalactic victim.

Type-Be stars, as they rapidly spin, collect matter from a companion star, the theory says. This matter then surrounds the star as a ring and causes the type-Be star to spin faster as it accumulates more from its companion. These companions, which become even smaller due to the loss of matter, can be anything from a neutron star to a white dwarf.

How they began the process of rapidly rotating and collecting matter, however, was a mystery. Regular type-B stars also had companions they weren't feasting upon, so what made the two different?

The researchers say a heretofore unobserved third star is likely facilitating the mass transfer by bringing the type-Be star and its companion closer together, just as a vampire's thrall could lead a victim to its master.

"We didn't go into the study thinking that we would find triples, rather we went in looking for how often these stars were in doubles, but based on our results, triples ended up being the most reasonable explanation for what we were seeing," Dodd said.

'Triples are the new doubles'

The University of Leeds scientists used data from European Space Agency satellites — the Hipparcos and the Gaia — to map out the universe's stars.

The team observed the type-Be stars by comparing the positions of various stars over longer and shorter periods. The team also looked at type-B stars to compare the two.

Researchers said that if the positions of the stars moved in a straight line, there was only one star in the system. If it wobbled or spiraled, one of the stars had a companion star. This is because gravitational forces influence the movement of the star.

However, the team was surprised to learn that they were detecting a higher rate of binary systems for type-B stars than for type-Be stars. Additionally, when researchers did find companions for the type-Be stars, the distances between their companions and those of the type-B stars — which do not have the characteristic rings — were fairly similar.

The researchers then expanded their search to see if the type-Be stars may have had companions at further distances. That's when the rate of companions began to even out between the type-B and type-Be stars.

This led researchers to believe the distant companion they observed with the type-Be stars was actually the third star.

Because three-star systems are inherently unstable, the stars, which begin close together, eventually eject one star. The force of the third star quickly ejecting from the group can pull the type-Be star and its companion star close together to commence the feeding.

Dodd told Business Insider that this phenomenon is most common in other triple-star systems, which also lent credence to their explanation that type-Be stars were no different.

Researchers said that this could also explain why the type-Be stars were observed to have lower rates of close companions — once the type-Be stars sucked all the mass from the companion stars, they became too faint to detect, the researchers speculated.

The team is now looking at future research to observe these type-Be stars further and hopes their study will help inform astronomers about other phenomena, such as black holes, neutron stars, or gravitational wave sources. Dodd said these "close-together" multiple-star systems could be the "progenitors" to these phenomena.

Dodd said their research also means scientists must start paying more attention to triple-star systems.

"Triples are the new doubles," Dodd said, "and the lives of stars are more often impacted by the presence of nearby stars than previously thought."