NASA's NuSTAR shows how stars explode

NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) has unraveled one of the biggest mysteries in astronomy of how stars blow up in supernova explosions.

The high-energy X-ray observatory has created the first map of radioactive material in a supernova remnant. The results, from a remnant named Cassiopeia A (Cas A), reveal how shock waves likely rip massive dying stars apart.

"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," Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology (Caltech) in Pasadena, said.

"Our new results show how the explosion's heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating," she said.

Cas A was created when a massive star blew up as a supernova leaving a dense stellar corpse and its ejected remains. The light from the explosion reached Earth a few hundred years ago, so we are seeing the stellar remnant when it was fresh and young.

NuSTAR is the first telescope capable of producing maps of radioactive elements in supernova remnants. In this case, the element is titanium-44, which has an unstable nucleus produced at the heart of the exploding star.

The NuSTAR map of Cas A shows the titanium concentrated in clumps at the remnant's center and points to a possible solution to the mystery of how the star met its demise. When researchers simulate supernova blasts with computers, as a massive star dies and collapses, the main shock wave often stalls out and the star fails to shatter.

The latest findings strongly suggest the exploding star literally sloshed around, re-energizing the stalled shock wave and allowing the star to finally blast off its outer layers.

The findings are published in the journal Nature.