'Then there were the observations of the debris. This picked up the presence of gold and other heavy elements in the debris, which again, clears up an outstanding mystery. Some heavy elements are readily formed in the environment created by a supernova, meaning it's easy to explain their abundance in the cosmos. But others can only form through pathways that involve the rapid ingestion of multiple neutrons—so fast that the atom doesn't have time to rearrange to accommodate the previous neutrons it had absorbed. Supernovae aren't thought to provide an environment that's sufficiently neutron-rich for this to occur.'
For more, read this article in Ars Technica.