The Aftermath of a Supernova     The explosion of the star with all of the elements inside can leave behind a large amount of dust and gas, this is called a nebula, but often  referred to as supernova remnant. The most famous being the crab nebula. The more massive the star was, it leaves different things. One other thing that is left behind from supernovae are neutron stars. When the core of the star is collapsing it "crushes" the protons and electrons together, making a super dense star made up of only neutrons. This creates the most dense object we know of with the mass of a star inside the diameter of about 20 km. with a density of about 10^17 kg/m^3. If the star was small enough, the dense neutron star can stop the collapse in its tracks. If the star was more massive, it can continue to collapse into a black hole, called a stellar black hole containing about 4 to 15 solar masses. A black hole crushes all of this mass down to a singularity, or a single point in space, creating one of the most intriguing phenomena in the universe.   Image taken from https://www.eso.org