Stunning Supernova Has Bubbly Interior

A new three dimensional model of the Cassiopeia A supernova remnant provides insights into how these massive explosions occur.

The detailed model reveals a bubble-like interior of debris that connects with a bright shell of ejecta arranged in multiple circular structures.

"This is the first time we've actually seen such a complete image of what the interior of this thing looks like," said one of the study's authors Professor Robert Fesen of Dartmouth College in New Hampshire.

"It shows big bubbles, big cavities that others suggested might be there, and this shows they really are."

The study is published in the journal Science.

Cassiopeia A was created 340 years ago when a massive star exploded to form a neutron star, making it a good subject for a cosmic post mortem.

In this type of explosion, known as a core-collapse supernova, the outer layers of the star drop in free fall, reaching speeds of 70,000 kilometers per second, a significant fraction of the speed of light.

Somehow, that material suddenly stops and ends up traveling the other way at up to 10,000 kilometers per second. Scientists call this sudden reversal a "bounce", but until now they've been unsure exactly how it happens.

"We know the core collapses down to form a neutron star, and the rest blows up somehow after that," said Fesen. "But most of our models have had problems blowing up stars because the outer layers of the star collapse into the core and smother the explosion!"

Stellar autopsy

Distant supernovae outside our galaxy are difficult to study because they're so far away.

Fesen and co-author Dr Dan Milisavljevic, of the Harvard-Smithsonian Center for Astrophysics, used near-infrared spectroscopy to measure expansion velocities of extremely faint material inside the supernova remnant, providing the crucial third dimension for the 3D model.

"We're sort of like bomb squad investigators," said Milisavljevic. "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."

The study revealed that cavities in the supernova's interior are caused by plumes of radioactive nickel 56, said Fesen.

"Nickel 56 will eventually decay into iron, and during that decay process a lot of energy is generated. These plumes of nickel move through the non-radioactive material, pushing it away and making cavities.

Read more at Discovery News