New Radiation Map Called "Holy Grail" of Supernova Observations

Cassiopeia A - a well-documented supernova remnant of a star that was once eight times the size of our Sun - has revealed what astronomers are calling a "holy grail observation" of astrophysics: a map of radioactive material thrown out from the star as it exploded in 1671 that explains how the star's core collapsed and formed either a neutron star or black hole.

For the first time, scientists have mapped the high-energy X-ray emissions of the radioactive isotope titanium-44 that were created in the actual core of the exploding star. When the supernova occurred, the star's core collapse blew away the star's outer layers, sending cosmic debris, such as this radioactive isotope, exploding outward. The material has been expanding outward ever since at speeds of 5,000 kilometers per second, the scientists report.

The observation was made possible by NASA's NuSTAR mission, which began in June 2012 with the goal of measuring high-energy X-ray emissions from exploding stars. Scientists from the University of California, Berkeley, were among the project's collaborators. They report their findings in the journal Nature.

"This has been a holy grail observation for high energy astrophysics for decades," said study co-author and NuSTAR investigator Steven Boggs, UC Berkeley professor and chair of physics. "For the first time we are able to image the radioactive emission in a supernova remnant, which lets us probe the fundamental physics of the nuclear explosion at the heart of the supernova like we have never been able to do before."

The find is exciting because it marks the first time scientists have information about the innards of a supernova explosion and what elements are produced when one occurs, said UC Berkeley astronomy professor Alex Filippenko, who was not part of the NuSTAR team.

With the new information, scientists can now build three-dimensional models of supernovae to better understand their characteristics.

"Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power," said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology. "Our new results show how the explosion's heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating."

The new map of titanium-44 does not synch with a map of elemental iron in the supernova's debris cloud, which has expanded to about 10 light years across since the distant supernova exploded 343 years ago.

"We don't know whether the iron was produced in the supernova explosion, whether it was part of the star when it originally formed, if it is just in the surrounding material, or even if the iron we see represents the actual distribution of iron itself, because we wouldn't see it if it were not heated in the shock," Boggs said.

The researchers contend that they may even be iron in the debris cloud which has yet to be detected.

"The surprising thing, which we suspected all along, is that the iron does not match titanium at all, so the iron we see is not mapping the distribution of elements produced in the core of the explosion," Boggs said.

The astronomers are observing other supernovae to compare their debris clouds with Cassiopeia A's in an attempt to determine if the debris pattern holds for other supernovae as well.