Remnants of a nearby supernova that exploded only 340 years ago has been well studied by scientists, but apparently still holds many mysteries. A new study has realized that Cassiopeia A (Cas A) is composed of a collection of about a half dozen massive cavities, or "bubbles," making the supernova look like "Swiss cheese."

A team at the Harvard-Smithsonian Center for Astrophysics (CfA) made the discovery using the astronomical equivalent of a CAT scan, thereby creating a 3D map of Cas A's interior. They hope that their findings will help them better understand how these massive explosions occur.

"Our three-dimensional map is a rare look at the insides of an exploded star," researcher Dan Milisavljevic at the CfA said in a statement.

"We're sort of like bomb squad investigators. We examine the debris to learn what blew up and how it blew up," he added.

When Cas A exploded hundreds of years ago, extremely hot and radioactive matter was ejected from its core, mixing and churning outer debris. The complex mechanisms behind these stellar explosions have been difficult for scientists to study, even with state-of-the-art simulations run on some of the world's most powerful supercomputers.

However, the CfA team has been successful in better understanding the processes at play by focusing on the supernova's remnants.

To create their 3D map, Milisavljevic and his colleagues examined Cas A in near-infrared wavelengths of light using the Mayall 4-meter telescope at Kitt Peak National Observatory in Arizona. Using spectroscopy allowed them to measure expansion velocities of extremely faint material in Cas A's interior, which gave them a sneak peak into the crucial third dimension.

Surprisingly, they found that the remnants of Cas A contain large interior cavities, the two main ones which are 3 and 6 light-years in diameter. And these Swiss cheese-like cavities, or "bubbles," help explain the previously observed large rings of debris that make up the Cas A's bright outer shell.

"Our study represents a major step forward in our understanding of how stars actually explode," Milisavljevic said.

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