Most of the matter in a star is blown away in the explosion ( forming nebulae such as the Crab Nebula ) but what remains will collapse into a neutron star ( a pulsar or X-ray burster ) or , in the case of the largest stars , a black hole . Most of the matter in the star is blown away by the supernova explosion ( forming nebulae such as the Crab Nebula ) and what remains will be a neutron star ( which sometimes manifests itself as a pulsar or X-ray burster ) or , in the case of the largest stars ( large enough to leave a stellar remnant greater than roughly 4 solar masses ) , a black hole .