Did Supernova 1987A leave behind a pulsar?
Astronomers feel confident SN 1987A left behind a rapidly spinning neutron star. Despite extensive searches and a few false detections, however, the quest to find it has turned up empty.
The physics of a core-collapse supernova is pretty straightforward. Once a star weighing more than about 8 solar-masses has cycled through its available nuclear fuel, its core ends up as an inert ball of iron. The core's mass continually increases as silicon in the overlying layer continues to fuse and dump more iron onto the core. Once the pressure exerted by electrons can no longer support the mounting weight, the core collapses.