Study reveals how ‘vampire’ star takes its victim in space

Astronomers have taken a good look at what happens when a “vampire” star sucks the layers of outer material from a companion star, reducing the “bite” victim to a mere stellar core.

Researchers said Wednesday that data obtained using telescopes from ESO (European Southern Observatory) in Chile shed light on the nature of a star system called HR 6819, showing that its two companion stars were not accompanied by a black hole. , as proposed earlier.

The two stars exist as a binary system, gravitationally married in an orbit that lasts about 40 days. While binary systems are common, what makes this one unique is that it provided a rare insight into the immediate consequences of what is called “stellar vampirism”.

“What we mean by stellar vampirism is that one star has sucked the outer material from another star,” said astronomer Abigail Frost of KU Leuven in Belgium, lead author of the research published in the journal Astronomy & Astrophysics.

“This can happen if the stars travel close enough to each other and the gravitational pull of one pulls material from the other.”

Stars grow slowly as they age. Those in binary systems with two orbiting close together — as in this case — can increase in size beyond a threshold where their gravity can protect them from the buoyancy of the companion. So, the fastest growing star is a victim of vampirism.

“When this occurs, the inner areas of the star that has been ‘bitten’ can be exposed, showing signatures of elements that would otherwise not be easy to see,” said Frost.

This binary system is located about 1,000 light-years — the distance light travels in a year, or 9.5 trillion km — from Earth.

A 2020 study proposed that this system contained what would have been the closest black hole to Earth — in a triple marriage with a star orbiting close to the black hole and another orbiting far away — but new data indicates otherwise.

Researchers who questioned the 2020 conclusion joined the new study with scientists involved in the previous work.

“It’s still a special system and, in my opinion, even more so,” said ESO astronomer Thomas Rivinius, co-author of the new study and lead author of the 2020 survey.

“Black holes exist in abundance because, once formed, they are permanent. This is not the case with what we see: this is a short-lived transitional stage — say, about 10,000 years — in the evolution of a special system. double star.”

The system has two B-type stars, which are large, very hot, very bright, and bluish in color. By way of comparison, our sun is a G-type star, less hot and smaller than the B-type ones.

The rapid rotation observed in the “vampire” star may have been caused by material from the other star that had previously fallen to its surface. The “vampire” now also has a disk of material around her. The stars orbit quite close together — a third of the distance that separates the Earth from the Sun — though not as close as some binary stars.

The current mass of the “vampire” star is approximately four to five times that of the sun. The mass of the other star, originally perhaps five to six times the mass of the sun, may now be less than one solar mass.

With vampirism, most of the external material sucked up from the larger star ends up incorporated into the thirsty companion.

“Because these outer layers were not touched by the nuclear combustion at the center of the original star, this material is ‘fresh,'” Rivinius said.

“And so the other aspect of ‘vampirism’ is that this supply of fresh hydrogen actually ‘rejuvenates’ the star that receives it, making it look bluer than it should be for its age.”

^{Translated by Luiz Roberto M. Gonçalves}