Question: How long does a supernova last?

Anna Scaife answered on 13 Nov 2014:

Hey Alia – the initial explosion from a supernova becomes really bright very quickly and then fades over a few weeks, but when the explosion happens it ejects a giant shell of material into space around it which accelerates away in all directions. That shell creates a giant shock front in space which accelerates the particles that it collides with to close to the speed of light and those particles then give out radiation in the X-ray and radio frequency bands. We call those supernova remnants and they can last for millions of years.

Since we know roughly how many supernovae happen every year in a galaxy we can predict how many supernova remnants we should be able to find in our own galaxy. Bizarrely there aren’t nearly as many as we expect and I spent all morning today talking to other astronomers about why that might be and how we could potentially detect more of them.