Utilizing NASA’s Imaging X-ray Polarimetry Explorer (IXPE) spacecraft, astronomers have obtained their first view of the interior area round a useless white dwarf star that’s vampirically feeding on a stellar companion.
The workforce from the Massachusetts Institute of Expertise (MIT) was capable of carry out an in depth examine of the beforehand inaccessible extremely energetic area instantly surrounding a white dwarf within the system EX Hydrae, positioned round 200 light-years from Earth.
Not solely did the researchers uncover a excessive diploma of polarization among the many X-rays, which describes settlement within the path the waves that comprise electromagnetic radiation are angled in, however they have been additionally capable of hint this energetic radiation to a 2,000-mile-tall (3,200 kilometers) column of blisteringly sizzling stellar materials being pulled from the companion star, dropping onto the white dwarf.
That is round half the radius of the white dwarf itself and far bigger than scientists had beforehand estimated for such a construction. The workforce additionally detected X-rays reflecting off the floor of the white dwarf earlier than being scattered, one thing that has been predicted however was by no means beforehand confirmed.
Intermediate polars earned their title as a result of variations within the power of white dwarfs’ magnetic fields. When the magnetic discipline is especially sturdy, these useless stars pull materials from their companion stars, which then flows towards the white dwarfs’ poles. Nevertheless, when the magnetic fields of white dwarfs are weak, stripped materials types swirling buildings referred to as accretion disks round white dwarfs. From there, this stolen stellar matter is then step by step fed to the surfaces of the stellar remnants.
The state of affairs is extra complicated for vampire white dwarfs with intermediate-strength magnetic fields. Scientists have predicted that, for these techniques, an accretion disk ought to nonetheless be shaped, nevertheless it needs to be dragged towards the poles of those white dwarfs. The magnetic fields in these techniques ought to then hoist up this materials, making a fountain of stellar matter, or an “accretion curtain,” that rains down on white dwarfs’ magnetic poles at tens of millions of miles per hour.
Scientists have predicted that this downward-flowing materials ought to slam into still-falling matter beforehand lifted by magnetic fields, creating columns of turbulent fuel that may attain temperatures of tens of millions of levels Fahrenheit, emitting X-rays within the course of.
In January 2025, the analysis workforce aimed to check this concept by learning the EX Hydrae system with round seven Earth-days’ price of observations performed with IXPE.
The findings display the effectiveness of a way referred to as “X-ray polarimetry,” which measures the polarization of X-rays, in learning excessive and violent stellar environments.
“We confirmed that X-ray polarimetry can be utilized to make detailed measurements of the white dwarf’s accretion geometry,” workforce chief Sean Gunderson, from MIT’s Kavli Institute for Astrophysics and House Analysis, stated in an announcement. “It opens the window into the opportunity of making comparable measurements of different forms of accreting white dwarfs that even have by no means had predicted X-ray polarization indicators.”
Polarized findings
Waves of sunshine oscillate at a proper angle to the path by which that mild is propagating, however the angle at which they oscillate could be influenced by magnetic and electrical fields. Moreover, when mild bounces off a floor, it may well change into polarized, that means the oscillation of sunshine waves is organized into a typical path. By learning polarized mild, researchers can be taught extra concerning the object it has scattered off.
Launched in 2021, IXPE is NASA’s first mission designed to detect polarized X-rays, with the spacecraft having studied a number of the universe’s most excessive objects and occasions, corresponding to neutron stars, black holes, and supernovae. That is the primary time that IXPE has been directed to check an intermediate polar system, a smaller object however nonetheless a powerful emitter of X-rays.
“We began speaking about how a lot polarization could be helpful to get an thought of what is taking place in some of these techniques, which most telescopes see as only a dot of their discipline of view,” stated workforce member Herman Marshall of MIT. “With each X-ray that is available in from the supply, you’ll be able to measure the polarization path. You accumulate quite a lot of these, they usually’re all at totally different angles and instructions, which you’ll be able to common to get a most popular diploma and path of the polarization.”
Marshall, Gunderson and colleagues discovered an 8% polarization diploma in X-rays from EX Hydrae, which is far larger than theoretical fashions predicted. Following this discovery, the scientists confirmed that the X-rays did certainly originate from a column of colliding fuel that’s round 2,000 miles tall.
“In the event you have been capable of stand considerably near the white dwarf’s pole, you’d see a column of fuel stretching 2,000 miles into the sky, after which fanning outward,” Gunderson stated.
By measuring the path of the polarization of those X-rays, the workforce was capable of verify that this high-energy radiation is bouncing off the floor of the white dwarf earlier than touring via house.
“The factor that is useful about X-ray polarization is that it is providing you with an image of the innermost, most energetic portion of this complete system,” workforce member and MIT scientist Swati Ravi added. “Once we look via different telescopes, we do not see any of this element.”
The workforce now intends to broaden its investigation of the environments round vampire stars past EX Hydrae to different feeding white dwarf techniques. This might in the end assist higher perceive the ultimate state of those techniques — the Sort Ia supernova explosions that emerge from the overfeeding of the useless stars and normally consequence within the whole destruction of the white dwarf.
“There comes a degree the place a lot materials is falling onto the white dwarf from a companion star that the white dwarf cannot maintain it anymore, the entire thing collapses and produces a kind of supernova that is observable all through the universe, which can be utilized to determine the scale of the universe,” Marshall concluded. “So, understanding these white dwarf techniques helps scientists perceive the sources of these supernovae, and tells you concerning the ecology of the galaxy.”
The workforce’s analysis was revealed on Nov. 10 in The Astrophysical Journal.
