NASA’s IXPE has just revealed the hidden geometry of a white dwarf’s cosmic feeding frenzy—using X-rays to see what no telescope could before.
Scientists have used NASA’s IXPE (Imaging X-ray Polarization Explorer) to study a white dwarf star for the first time. By measuring the polarization of X-rays, the mission allowed astronomers to investigate the structure of a highly energetic binary star system known as EX Hydrae. The observations revealed new details about how matter behaves in extreme environments where gravity and magnetism collide.
A Week-Long Observation of EX Hydrae
IXPE observed EX Hydrae for nearly a full week in 2024. The system is located in the constellation Hydra, about 200 light-years from Earth. The findings were published in the Astrophysical Journal. The research was led by astrophysicists at the Massachusetts Institute of Technology in Cambridge, with collaborators from the University of Iowa, East Tennessee State University, the University of Liége, and Embry Riddle Aeronautical University.
A white dwarf forms when a star exhausts the hydrogen fuel in its core but does not have enough mass to explode as a core-collapse supernova. The remaining stellar core becomes extremely dense, packing roughly the mass of the Sun into a body about the size of Earth.
A Binary System Fueled by Stolen Gas
EX Hydrae is part of a binary system that includes a normal main sequence star. Gas from that companion star is constantly flowing toward the white dwarf. The way this material is gathered, a process known as accretion, and where it lands on the white dwarf are controlled by the strength of the white dwarf’s magnetic field.
In EX Hydrae, the magnetic field is too weak to channel all incoming matter directly onto the star’s poles. However, the system still rapidly accumulates material in a surrounding accretion disk. This combination places EX Hydrae in a category known as “intermediate polars.”
Extreme Heat and Powerful X-Rays
In intermediate polar systems, gas forms a spinning accretion disk while also being guided toward the white dwarf’s magnetic poles. As the material crashes inward, it heats up to tens of millions of degrees Fahrenheit. The inflowing gas collides with other material trapped by the white dwarf, forming towering columns of superheated plasma that release intense X-rays, making the system an ideal target for IXPE.
“NASA IXPE’s one-of-a-kind polarimetry capability allowed us to measure the height of the accreting column from the white dwarf star to be almost 2,000 miles high – without as many assumptions required as past calculations,” said Sean Gunderson, MIT scientist and lead author on the paper. “The X-rays we observed likely scattered off the white dwarf’s surface itself. These features are far smaller than we could hope to image directly and clearly show the power of polarimetry to ‘see’ these sources in detail never before possible.”
The polarization data collected from EX Hydrae will help astronomers better understand other high-energy binary systems throughout the universe, especially those involving strong magnetic fields and intense X-ray emissions.
More About the IXPE Mission
The IXPE mission continues to deliver unique data that is driving new discoveries about extreme cosmic objects. It is a joint effort between NASA and the Italian Space Agency, with science partners in 12 countries. The mission is led by NASA’s Marshall Space Flight Center in Huntsville, Alabama. Spacecraft operations are managed by BAE Systems, Inc., based in Falls Church, Virginia, in collaboration with the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder.
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