Watch: This 'vampire star' is eating its companion
What's the story
Astronomers using NASA's Imaging X-ray Polarimetry Explorer (IXPE) have captured a rare sighting of a "vampire star" feeding on its companion. The research team from the Massachusetts Institute of Technology (MIT) studied the high-energy region around a white dwarf in the EX Hydrae system, located some 200 light-years away. This is the first time scientists have been able to observe the accretion geometry of such a system in detail using X-ray polarimetry.
Stellar duo
EX Hydrae: A unique binary star system
The EX Hydrae system is an "intermediate polar," a class of stars known for their complex radiation patterns, including X-rays. It consists of a white dwarf, the final phase of stars similar to our Sun, and its companion star that orbits the dead star every 98 minutes. This makes EX Hydrae one of the closest intermediate polar binaries ever discovered.
Stellar structure
Discovery of a towering column of stellar material
The research team found a high degree of polarization in the X-rays, indicating that they come from a 3,218km-tall column of hot stellar material being pulled from the companion star and falling onto the white dwarf. This is about half the radius of the white dwarf itself and much larger than previously thought for such structures. The team also detected X-rays reflecting off the surface of the white dwarf before scattering, something that had been predicted but never confirmed.
Feeding mechanism
Intermediate polars have a complex feeding process
Intermediate polars are named for having magnetic fields of intermediate strength, which influence how they accrete material from companion stars. When these fields are strong, they pull material from companion stars that falls onto their poles. But when the magnetic fields are weak, stripped material forms accretion disks around white dwarfs. This stolen stellar matter is then gradually fed to the surfaces of these stellar remnants.
Feeding dynamics
Vampire white dwarfs and their unique feeding patterns
Vampire white dwarfs with intermediate-strength magnetic fields are more complex. Scientists think these systems should form an accretion disk that gets dragged toward the poles of these white dwarfs. The magnetic fields in these systems must then lift this material, creating a fountain of stellar matter or an "accretion curtain," that rains down on the white dwarfs' magnetic poles at millions of miles per hour.