Scientists use new NASA tool to map the remains of an exploded star

Using NASA’s Imaging X-ray Polarimetry Explorer (IXPE), astronomers have measured and mapped polarized X-rays from the remains of an exploded star called Cassiopeia A, shedding new light on the nature of young supernova remnants, according to a press statement by NASA published on Tuesday.

Measuring the polarization of X-ray light

IXPE is a collaboration between NASA and the Italian Space Agency launched on December 9, last year. It is the first satellite that can measure the polarization of X-ray light with this level of sensitivity and clarity.

“All forms of light – from radio waves to gamma rays – can be polarized. Unlike the polarized sunglasses we use to cut the glare from sunlight bouncing off a wet road or windshield, IXPE’s detectors maps the tracks of incoming X-ray light. Scientists can use these individual track records to figure out the polarization, which tells the story of what the X-rays went through,” explained NASA in its release.

Cassiopeia A (Cas A for short) was the first object IXPE observed after it began collecting data selected because its shock waves are some of the fastest in the Milky Way.

“Without IXPE, we have been missing crucial information about objects like Cas A,” said Pat Slane at the Center for Astrophysics | Harvard & Smithsonian, who leads the IXPE investigations of supernova remnants. “This result is teaching us about a fundamental aspect of the debris from this exploded star – the behavior of its magnetic fields.”

By studying the polarization of Cas A’s light, scientists can “reverse engineer” what’s happening inside the star at very small scales. However, before IXPE, scientists predicted X-ray polarization would be produced by magnetic fields that are perpendicular to magnetic fields observed by radio telescopes. They were wrong.

A big surprise

IXPE data showed that the magnetic fields in X-rays tend to be aligned in radial directions even very close to the shock fronts.

"These IXPE results were not what we expected, but as scientists we love being surprised,” said Dr. Jacco Vink of the University of Amsterdam and lead author of the paper describing the IXPE results on Cas A. “The fact that a smaller percentage of the X-ray light is polarized is a very interesting – and previously undetected – property of Cas A.”

Now, the astronomers plan to use IXPE to study other celestial objects and hopefully get similar results.

“This study enshrines all the novelties that IXPE brings to astrophysics,” said Dr. Riccardo Ferrazzoli with the Italian National Institute for Astrophysics/Institute for Space Astrophysics and Planetology in Rome.

“Not only did we obtain information on X-ray polarization properties for the first time for these sources, but we also know how these change in different regions of the supernova. As the first target of the IXPE observation campaign, Cas A provided an astrophysical 'laboratory' to test all the techniques and analysis tools that the team has developed in recent years.”