Hobbies And Interests
Understanding Stars
To explain what a supernova is and how it occurs you first need to explain what a star is. At fifth grade most kids can understand that the energy coming from a star is not the result of it burning but the result of the atoms being joined together and releasing energy. However, the thing they really need to understand is that the explosive force of the star pushing outwards is matched by the force of gravity. This means the star is under massive tension, being pushed out and pulled out by equally massive forces. Most kids at this age already understand that gravity is caused by heavy things so this should make sense. You can illustrate this with a balloon being blown up -- the air wants to push it out, the elasticity wants to pull it in -- when the forces are balanced it stays the same size.
Collapse
Once they understand the idea of stars being held together by gravity and explosive force ask them what would happen if the fuel for the star ran out. They will probably be able to tell you that the gravity will take over and draw everything inwards. Now ask them if they think it collapses gently or powerfully. Ask them what they think happens when lots of matter gets slammed together really hard. They will probably be able to guess that it is an explosion. This about as complex as it needs to be at fifth grade.
Extra Fuel
Explain that it is not just planets that orbit stars, but that sometimes two stars can be in orbit around each other. Ask them want they think would happen to matter that spills out from one star. They will probably know that it will get pulled into the other star but prompt them if needs be. Now ask them what happens if the pull between the two stars is slightly stronger than the force pulling them outward. They will probably be able to see that they will get pulled into each other slowly. Now explain that in either case it means a lot more fuel going into the star. Now go back to the idea of the star being in a balance of explosive force and gravity. Ask them what happens if you suddenly put more fuel in the fire. If they answer that the explosive force becomes stronger than gravity and this makes the star explode then that is great and you might want to stop there. However they might ask why the extra mass doesn't mean more gravity, which would balance the extra force. Explain that the extra pressure means that the fuel can burn hotter, making it get even hotter, creating more pressure.
The Leftovers
Once you have discussed the explosion occurring when a star collapses and explained that it blasts some of the outer matter into space, ask what they think might happen to the leftover matter. Try to explain that as it gets closer together it becomes denser, which increases the gravitational force and pulls it in even tighter. Explain that sometimes this creates a neutron star, which is a very hot, very dense, tiny star not much bigger than a city, or if it is below a certain size, keeps on collapsing, becoming infinitely dense, until its gravity is so strong that even light cannot escape from it. This is a black hole.