Question: What are supernova remnants?

Miranda Jackson answered on 22 Jun 2015:

When a star more massive than 8 times the mass of the sun runs out of fuel, its core collapses, which causes a supernova explosion. Another type of supernova (type Ia) happens when a white dwarf has attracted material from a larger companion star onto itself and reaches a certain mass. Either way, this causes a shock wave to travel out into space, heating up gas and dust it encounters as it expands. The hot gas cloud glows in different colours, and it looks quite beautiful. This is a supernova remnant. We can tell what type of star caused the supernova and how long ago the explosion occured by studying a supernova remnant.