Algodoo

I randomly threw together a bunch of circles, made them have high attraction and 1 restitution, and got this. It looks and acts like a star, except that it's green instead of red yellow or blue. (I just thought green looked better than the others. Also it makes it easier to see.)

If you leave it alone, it starts to quiver and jiggle. That's it heating up. When you leave it for long enough, it will start to shake very violently. Then eventually it will create small explosions. If you leave it long enough, it will explode apart completely and reform in a few seconds.

It's not very stable. The longest I got it to stay together for was about 10 seconds, but what're ya going to do, it's a star. They'll do that to ya.

Should work in phun, because it just uses basic material settings, but it might not because algodoo physics are a bit different than phun physics.