Scientists get 1st good look at a ‘vampire star’ feeding on its victim

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Thanks to NASA’s Imaging X-ray Polarimetry Explorer (IXPE) spacecraft, astronomers have obtained their first view of the interior region around a dead white dwarf star that vampirically feeds on a stellar companion.

The Massachusetts Institute of Technology (MIT) team was able to perform a detailed study of the previously inaccessible, highly energetic region immediately surrounding a white dwarf in the EX Hydrae system, located approximately 200 light years of the Earth.

The system is part of a class called “intermediate polar”, known to emit a complex pattern of radiation, including X-rays. EX Hydrae includes a white dwarf, the final stage in the life of stars of similar mass to the sunand its victim star, which completes an orbit around the dead star every 98 minutes. This makes EX Hydrae one of the closest intermediate polar binaries ever discovered.

Not only did the researchers discover a high degree of polarization between the

That’s about half the radius of the white dwarf itself and much larger than scientists previously estimated for such a structure. The team also detected X-rays reflected from the white dwarf’s surface before being scattered, which has been predicted but never previously confirmed.

Intermediate polars owe their name to variations in the strength of the magnetic fields of white dwarfs. When the magnetic field is particularly strong, these dead stars extract material from their companion stars, which then flows toward the poles of white dwarfs. However, when the magnetic fields of white dwarfs are weak, the stripped matter forms swirling structures called accretion disks around the white dwarfs. From there, this stolen stellar material is then gradually delivered to the surfaces of the stellar remnants.

The situation is more complex for vampire white dwarfs with magnetic fields of intermediate strength. Scientists predicted that, for these systems, an accretion disk should still form, but it should be pulled toward the poles of these white dwarfs. The magnetic fields of these systems should then lift this material, creating a fountain of stellar material, or an “accretion curtain,” that rains down on the white dwarfs’ magnetic poles at millions of kilometers per hour.

Scientists predicted that this downward-flowing material would impact free-falling material previously lifted by magnetic fields, creating columns of turbulent gas that could reach temperatures of millions of degrees Fahrenheit, emitting X-rays.

In January 2025, the research team aimed to test this idea by studying the EX Hydrae system with approximately seven Earth days of observations made with IXPE.

The results demonstrate the effectiveness of a technique called “X-ray polarimetry”, which measures the polarization of X-rays, in studying extreme and violent stellar environments.

“We have shown that X-ray polarimetry can be used to make detailed measurements of the accretion geometry of the white dwarf,” said team leader Sean Gunderson of MIT’s Kavli Institute for Astrophysics and Space Research. said in a statement. “This opens the possibility of making similar measurements on other types of accreting white dwarfs for which no X-ray polarization signal has ever been predicted.”

Polarized results

Light waves oscillate at right angles to the direction in which that light is propagating, but the angle at which they oscillate can be influenced by magnetic and electric fields. Additionally, when light bounces off a surface, it can become polarized, meaning that the oscillation of light waves is organized in a common direction. By studying polarized light, researchers can learn more about the object it scattered.

Launched in 2021, IXPE is NASA’s first mission designed to detect polarized X-rays, with the spacecraft having studied some of the most extreme objects and events in the universe, such as neutron starsblack holes and supernovae. This is the first time that the IXPE has been tasked with studying an intermediate polar system, a smaller but still powerful X-ray emitting object.

“We started discussing the usefulness of polarization to get a sense of what’s going on in these types of systems, which most telescopes see as just a point in their field of view,” said MIT team member Herman Marshall. “With each X-ray coming from the source, you can measure the direction of polarization. You collect a lot of them, and they are all at different angles and directions, which you can average to get a preferred degree and direction of polarization.”

Marshall, Gunderson and their colleagues found an 8% degree of polarization in EX Hydrae’s X-rays, which is much higher than predicted by theoretical models. Following this discovery, scientists confirmed that the X-rays were indeed coming from a colliding column of gas measuring approximately 2,000 miles high.

“If you could stand a little bit near the white dwarf’s pole, you would see a column of gas extending 2,000 miles into the sky and then fanning outward,” Gunderson said.

By measuring the polarization direction of these X-rays, the team was able to confirm that this high-energy radiation bounces off the white dwarf’s surface before traveling into space.

“What’s useful about X-ray polarization is that it gives you a picture of the innermost, more energetic part of this whole system,” added team member and MIT scientist Swati Ravi. “When we look through other telescopes, we don’t see any of these details.”

The team now intends to expand their research into environments around vampire stars beyond EX Hydrae to other feeding white dwarf systems. This could ultimately help to better understand the end state of these systems – the Type Ia supernova explosions that emerge from the supercharging of dead stars and usually result in the total destruction of the white dwarf.

“There comes a point when so much material falls on the white dwarf from a companion star that the white dwarf can no longer hold it, the whole thing collapses and produces a type of supernova observable throughout the universe, which can be used to determine the size of the universe“, Marshall concluded. “So understanding these white dwarf systems helps scientists understand the sources of these supernovae and tells you about the ecology of the galaxy.”

The team’s research was published November 10 in The Journal of Astrophysics.