NASA’s IXPE unlocks hidden X-ray secrets of a white dwarf, showing how a dead star still feeds

This artist’s concept depicts a smaller white dwarf star pulling material from a larger star, right, into an accretion disk. Earlier this year, scientists used NASA’s IXPE (Imaging X-ray Polarization Explorer) to study a white dwarf star and its X-ray polarization. (Image: MIT/Jose-Luis Olivares)

NASA’s IXPE has, for the first time, used X-ray polarimetry to study a white dwarf system called EX Hydrae, revealing the structure of its hot, accreting gas columns. The observations helped scientists measure how matter flows from a companion star onto the white dwarf, offering new insight into energetic binary systems.

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Scientists have, for the first time, used NASA’s IXPE to study a white dwarf star. The research focuses on the binary system EX Hydrae and examines how extreme stellar environments behave. The findings were published in the Astrophysical Journal and reported this year, offering new insight into energetic binary systems observed using X-ray polarisation.

What scientists observed using IXPE

In 2024, NASA’s Imaging X-ray Polarization Explorer observed EX Hydrae for nearly one week. The system lies in the Hydra constellation around 200 light-years away. Researchers analysed X-ray polarisation data collected during this focused observation. The study was led by astrophysics researchers at the Massachusetts Institute of Technology. Scientists from the University of Iowa, East Tennessee State University, the University of Liége, and Embry Riddle Aeronautical University also contributed. This marks the first peer reviewed paper using data from IXPE.

How white dwarf systems behave

White dwarf stars form after exhausting hydrogen fuel reserves. These stars lack sufficient mass to explode as supernovae. What remains is an extremely dense stellar core. Such stars are similar in size to Earth but contain mass comparable to the Sun. EX Hydrae exists in a binary system with a main sequence companion star. Gas from the companion continuously falls toward the white dwarf.

The way matter accumulates depends on magnetic field strength. Strong fields direct material straight onto stellar poles. Weaker fields allow rotating accretion disks to form. EX Hydrae belongs to a class known as intermediate polars. Its magnetic field only partially channels incoming material. Matter both circles the star and flows toward magnetic poles simultaneously.

What the findings mean for astrophysics

As material falls inward, temperatures rise dramatically. Gas reaches tens of millions of degrees Fahrenheit. Large columns form above the white dwarf surface. These columns emit intense high-energy X-rays. NASA’s IXPE is uniquely suited to study such emissions. Its polarimetry capability allowed scientists to measure accretion column heights. The columns were found to extend nearly 2,000 miles high. Lead author Sean Gunderson said fewer assumptions were needed than before. The X-rays likely scattered off the white dwarf surface itself. Such features remain far too small to image directly.

The findings help scientists understand other energetic binary systems. They improve knowledge of how matter behaves under extreme gravity. IXPE is a joint NASA and Italian Space Agency mission. The project involves partners and scientists from 12 countries. NASA’s Marshall Space Flight Center leads the mission. Spacecraft operations are managed by BAE Systems with university support. IXPE continues to reveal new details about energetic objects across the universe.