While exploding, supernovas not spherical

Giant stars are slightly off-kilter as they go kablooey, research in the Feb. 20 Nature suggests.

When massive stars run out of elements to fuse in their core, they collapse under their own gravity; the imploding material then bounces off the core and explodes in a bright display known as a core-collapse supernova. But computer simulations indicate that if material collapses symmetrically, as scientists long assumed, a star would not explode.

To address this conundrum, a team including Caltech astrophysicist Brian Grefenstette pointed NASA’s recently launched Nuclear Spectroscopic Telescope Array at Cassiopeia A, the remnant of a nearby core-collapse supernova whose light first reached Earth about 350 years ago. The researchers plotted the spatial distribution of high-energy X-rays emitted during the decay of the radioactive element titanium-44, which is forged in the depths of supernova explosions.

The X-rays revealed that the titanium is concentrated in several dense clumps, which suggests that the explosion was not symmetrical. The study offers an unprecedented look at a supernova’s inner workings, Grefenstette says, bringing scientists closer to learning exactly how these spectacular cosmic fireworks get set off.