Laura Lopez of the University of California at Santa Cruz and her colleagues looked at supernova remnants in the Milky Way and a neighbouring galaxy, the Large Magellanic Cloud. Results showed that Type Ia supernovas left behind relatively symmetric, circular remnants, while debris from Type II supernovas was distinctly more asymmetric. When the stellar guts spew out into space, they also heat up the interstellar medium nearby, and so Lopez thinks the symmetry could tell astronomers something about that medium.
"It seems that Type Ia supernovas probably go off in a very low-density medium that's very homogenous whereas core-collapse supernovas probably go off in a very dense environment that is not uniform" - Laura Lopez.
One of the remnants, known as SNR 0548-70.4, was a bit of an oddball, the researchers found. Based on its chemical abundances, SNR 0548-70.4 was considered a Type Ia supernova, but Lopez found it was asymmetric, suggesting a core-collapse remnant.