Hello, I want to understand: just as the Crab Nebula is the result of SN 1054 and has a neutron star spinning at the center: (a) Does all supernova produces a nebula? (b) Does all supernova remnant has a neutron star at the center? (c) What is the outcome of Kepler supernova i.e. SN 1604? I mean to ask has it formed a stellar remnant or a neutron star? (d) Say, if we consider a supernova, S, which has happened in the year 1000, then the stellar remnant, the neutron star or whatever other outcomes have come in that supernova, does it remain forever? I mean to say, is there a specific time duration, after which things die out and nothing is there from that specific supernova? Thanks.