Observations recorded in a study by researchers at the Harvard-Smithsonian and Dartmouth College have shed light on the interior of the much-studied exploded star, Cassiopeia A. Using the astronomical equivalent of a CAT scan, the team created an interactive 3D map of the exploded star, showing that the supernova remnant is made up of a series of massive cavities.

The star, known as Cas A, exploded some 340 years ago, pushing hot radioactive matter out from its core and mixing it with the outer debris. Due to its complexity, modelling the physics of a supernova explosion is, historically, extremely difficult.

"We’re sort of like bomb squad investigators," Dan Milisavljevic of the Harvard-Smithsonian Center for Astrophysics (CfA) said of the research. "We examine the debris to learn what blew up and how it blew up. Our study represents a major step forward in our understanding of how stars actually explode."

With this purpose in mind, the team created a 3D map using near-infrared observations from the Mayall 4-meter telescope at the Kitt Peak National Observatory in Tucson, Arizona. To map the third dimension, they made use of spectroscopy – measuring the expansion velocities of materials that appear faint in the exploded star’s interior.

The resulting 3D map reveals a series of cavities (around half a dozen in total) that the researchers describe as having a "swiss cheese-like structure." The largest of the cavities are three and six light years in diameter, and the structure is thought to have been created by plumes of radioactive nickel during the explosion.

As nickel decays to form iron, it’s thought that a large amount of the material should now reside within the cavities, but previous observations have failed to detect it. As the properties of the iron are unknown, it’s difficult to predict which future instruments would successfully be able to do so.

Next generation telescopes, in particular the James Webb Space Telescope, will provide data that shows the remnant in greater depth than ever before, and will, the team hopes, uncover the elusive material.

The CfA’s planned Smart-X X-ray telescope may also play a role in the potential discovery, with its readings improving upon the sensitivity of current stalwart Chandra, while maintaining that telescope’s high spatial resolution.

The findings of the CfA study were published in the journal Science on January 30.

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