Some 200 light years from Earth, a dead star’s core is locked in a violent orbit with a larger companion — a swirling stellar duet known as an “intermediate polar.” As the white dwarf’s intense magnetic field siphons gas into an accretion disk, the system unleashes complex, high-energy radiation that has long eluded detailed study.
Now, MIT astronomers have used NASA’s IXPE X-ray telescope to peer into the innermost region of this system, EX Hydrae, revealing a surprisingly clear X-ray polarization signature. The direction and strength of this polarization allowed the team to pinpoint the origin of the radiation: a towering, white-hot accretion column about 2,000 miles high — roughly half the white dwarf’s radius, and far larger than theorists expected.
The observations also provide the first confirmation that X-rays in such systems reflect off the white dwarf’s surface before scattering into space, shaping the radiation we detect.
The study, published in The Astrophysical Journal, shows that X-ray polarimetry can map the geometry of extreme stellar environments with unprecedented precision — opening the way to similar insights across a broader class of accreting white dwarfs.
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