Since neutrinos appeared worldwide in 1987 and a supernova in the neighborhood was registered shortly afterwards, observations, measurements and speculations have been ongoing. The latest ones not only show different elements, but also provide a glimpse of what is left behind.https://www.notebookcheck.net/Supernova-remeasured-View-into-the-center-of-the-stellar-explosion.806645.0.html
a (near) infinitely dense structure...remains.
the only known "infinitely dense structure" we know of today is a black hole.