What makes a supernova explode?

Answer 1

Think of a house. This house we're talking about has one main support beam, and as time passes, it begins to need something to strengthen said support. A star is a lot like a house with a bad support beam. It uses its own fuel to keep burning and avoid failing. A house would need workers to put something on the beam to keep it steady. But, let's say that after 10 million years or so, the workers get laid off, or find other jobs. The support beam still needs to be serviced, but the service it now has is less than what is needed, or may provide adverse effects. When a superstar exhausts its hydrogen fuel, it begins burning it's helium, causing it to swell and become redder and cooler. Let's say that someone is nailing planks of wood into the beam of this house to support it better. But, the support beam is too old, and as each piece of wood is nailed to it, it develops cracks and becomes weaker. As the star runs out of helium, it begins burning heavier elements. Finally, the house can't stand it anymore and the beam gives way, sending the entire house crashing down violently. In a way, the support beam had been fighting a war against gravity, and finally lost. That's very much what happens to stars. A supernova is caused when a superstar (now a Red Supergiant) fuses iron in it's core. It takes the star more energy to make the iron than the iron can actually produce, and the star then collapses in on itself, losing it's own lifelong battle against gravity.

In a nutshell, when a superstar fuses iron.... all hell breaks loose.