Researchers at the University of Notre Dame have identified the first magnetic propeller in a variable star system. This became known from the Astrophysical Journal.
The J0240 star system is only the second such system in history. It was identified in 2020 as an unusual cataclysmic variable – a binary system consisting of a white dwarf star and a red giant. Usually, a compact white dwarf star collects gas and increases its mass. However, in J0240, a rapidly rotating magnetic white dwarf rejects gas and pushes it out of the binary system.
“To have such a propeller, you need a fast spinning dwarf with a strong magnetic field,” said Peter Garnavich, professor of astrophysics and chair of physics at Notre Dame and lead author of the study that presented evidence for the system. – Usually the gas escaping from the donor star enters the orbit of the white dwarf. But in this case, gas is ejected from the binary star in a wide spiral, forming a propeller. ”
White dwarfs are the cores of burned-out small stars devoid of their energy sources. They arise in the last stages of the life of celestial bodies, which are no more than ten times heavier than the Sun. However, without a companion star, the object will never become part of the system of cataclysmic variables.
The only other cataclysmic variable similar to J0240 is AE Aquarii, a binary star system known since the 1950s. However, in J0240, it is observed near the orbital plane of the binary system, which means that the gas ejected from the system is visible as a silhouette against the background of starlight. This is the first direct evidence that a magnetic propeller is ejecting gas from a red star.
“The uniqueness of the system lies in the fact that we can actually see the clots of gas ejected by the propeller,” the scientists noted. “This gas blocks some of the light from both stars, and we can see this absorption in our data.”