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Sometimes progress in space science does not arrive with a flash. It comes quietly, through patient observation, and then settles into place. That is how this new result from NASA’s Imaging X-ray Polarisation Explorer fits. For the first time, the mission has been used to study a white dwarf star, not as a distant point of light, but as a structured system with shape and depth. The target was EX Hydrae, a compact stellar remnant paired with a normal star, slowly pulling material towards itself. By watching how X-rays behave rather than just how bright they are, scientists were able to learn something new about how these extreme systems work. It is a small shift, but one that opens new ways of seeing familiar objects.
NASA measures a white dwarf star for the first time
EX Hydrae sits about 200 light years away in the constellation Hydra. It belongs to a class of objects known as white dwarfs. These stars are what remain after a sun like star runs out of fuel. They do not explode. They collapse into something dense and compact, roughly the size of Earth but holding a mass similar to the Sun.EX Hydrae is not alone. It is part of a binary system, orbiting closely with a companion star that is still burning hydrogen. Gas from that companion spills across space and falls towards the white dwarf. This slow transfer of material powers much of what astronomers observe from the system.
How does an intermediate polar system behave
Not all white dwarf binaries behave the same way. The key difference often lies in magnetism. Some white dwarfs have very strong magnetic fields that pull material straight down onto their poles. Others have weaker fields that allow gas to form a flat accretion disc before it settles.EX Hydrae sits in between. Its magnetic field is strong enough to disturb the disc but not strong enough to dominate it fully. Systems like this are known as intermediate polars. Gas spirals inward, then gets redirected along magnetic field lines towards the star’s surface. As it falls, the material heats to tens of millions of degrees and produces high energy X-rays.
NASA’s IXPE able to observe something new
IXPE does something other telescopes do not. Instead of only measuring how much X-ray light arrives, it also measures how polarised that light is. Polarisation carries information about direction and structure. It can hint at where light was scattered and how it moved through space.In 2024, IXPE observed EX Hydrae for nearly a week. Using its data, researchers could estimate the height of the column of hot gas above the white dwarf. They found it rose almost 2,000 miles above the surface. That measurement required fewer assumptions than earlier models.The data also suggested that some X-rays were bouncing off the white dwarf’s surface before reaching Earth. This kind of detail cannot be imaged directly. Polarisation makes it visible indirectly.
The scientists behind this research
The study was led by scientists at the Massachusetts Institute of Technology, with collaborators from several universities in the United States and Europe. Their results were published in the Astrophysical Journal.Lead author Sean Gunderson noted that IXPE’s polarimetry made it possible to see features that would otherwise remain hidden. These structures are too small and too distant to resolve with traditional imaging. Yet their effects on light can still be measured.This approach gives astronomers a way to test models rather than rely only on theory.
What this means for future studies
EX Hydrae is only one system, but it is a useful one. Many energetic binary systems across the galaxy share similar physics. Understanding how matter behaves near a white dwarf helps scientists interpret other X-ray sources.IXPE is a joint mission between NASA and the Italian Space Agency, with partners in many countries. It continues to collect data on objects ranging from neutron stars to black holes.This result does not change everything at once. It adds a layer. It shows that by paying attention to how light behaves, not just how bright it is, astronomers can begin to map environments that were previously out of reach. The universe stays the same. Our view of it does not.
