Astronomers recently got a rare look at a white dwarf star in the EX Hydrae system, about 200 light-years away. This white dwarf is engaging in a “vampire” act, drawing material from its companion star. A team from MIT utilized NASA’s IXPE spacecraft to uncover details about this intriguing system.
EX Hydrae is classified as an “intermediate polar” because of the complex radiation it emits, including X-rays. The white dwarf here is the final stage of a star’s life cycle, similar to our Sun. It pulls material from a companion star, which orbits it every 98 minutes, making this one of the closest systems of its kind.
The researchers discovered strong polarization among the emitted X-rays. This polarization indicates how the light waves are aligned, providing insights into the nearby energetic regions. They tracked this radiation to a massive column of superheated gas, about 2,000 miles high, falling onto the white dwarf. This structure is much larger than scientists originally expected.
White dwarfs can have different magnetic field strengths. When a white dwarf has a strong magnetic field, it attracts material from its companion star, which can then form an accretion disk around it. When the magnetic field is weak, the material can spiral inward, forming complex structures. In intermediate polars like EX Hydrae, researchers think a combination occurs, forming what’s referred to as an “accretion curtain,” which can rain material at incredibly high speeds onto the white dwarf’s poles.
In January 2025, the team plans to observe EX Hydrae for about seven days to further investigate these phenomena. Their results show how effective X-ray polarimetry is in studying extreme cosmic environments.
Sean Gunderson, the project’s lead from MIT’s Kavli Institute for Astrophysics, emphasized the potential for this technique. “We can make detailed measurements that give insights into other types of white dwarfs that also haven’t shown predicted polarization signals,” he said.
The IXPE mission, launched in 2021, marks the first attempt to study polarimetry in X-rays. Previously, it has examined extreme cosmic objects like neutron stars and black holes. Team member Herman Marshall noted that the IXPE was able to detect an 8% degree of polarization, which is higher than expectations.
By analyzing the direction of this polarization, the team confirmed that the X-rays originate from the gas column colliding. “If you were close to the white dwarf’s pole, you’d see a vast column of gas stretching high above,” Gunderson explained.
The team intends to expand this research to include more “vampire stars.” Understanding these systems may provide clues about Type Ia supernovae, which significantly contribute to our understanding of the universe’s size.
As Marshall pointed out, the ultimate fate of these white dwarfs is significant not just for their own life cycle but for our broader knowledge of the galaxy’s ecological systems. “Studying these white dwarf systems can help us trace the origins of supernovae,” he said.
For those interested in the details, this research was published in The Astrophysical Journal on November 10. To learn more, you can check out the original study here.
