The Galilean Cannon experiment supposedly models how supernovas work. Could someone possibly explain how the concepts correlate in simple terms?
In: 1
It helps explain how some kinds of supernovas “explode”. Star aren’t chemical reactions like conventional explosives, they’re great big (unimaginably big) stable-ish nuclear fusion reactors. They have enormous gravity trying to pull them into a tiny ball and enourmous fusion pressure trying to blow them up. Those two forces balance out through most of the star’s life…up until the star runs out of fuel.
Now the fusion pressure disappears and the star starts to cool, but gravity is still going full strength. The star collapses inwards. Until everything runs into each other at the center…and here’s where the Galilean Cannon comes in.
Imagine a big iron plate with a whole bunch of Galilean Cannons on it, and we set them off all at once…all the top balls from the cannon will fly *way* up into the air.
Now wrap that iron plate into a sphere, so the Galilean Cannons point outwards like spikes on a porcupine. And set all the cannons off again (gravity is now “in”, towards the center of the sphere). All the top balls in the cannons go rocketing off in all directions.
That’s what’s happening when the star collapses. The balls of the cannon are like the progressively denser layers of the star. “Firing” the cannon is when stellar fusion stops and all those layers fall inwards towards the center. They “bounce” off the stellar core, transfering almost all that kinetic energy (which is recovered gravitational potential energy) into the outer/lighter layers and throwing the outer layers of the star outwards at ludicrous velocity, a stellar explosion.
The [Galilean Cannon](https://en.wikipedia.org/wiki/Galilean_cannon) is basically a demonstration of the conservation of momentum. Create a stack of increasing size balls, then drop them from a height. The small ball shoots up a lot higher because the momentum of the entire stack is conserved and transferred to the small ball.
Stars have two competing actions: fusion, which wants to push things out, and gravity, which wants to pull things in. For most of the life of a star, fusion is enough to keep gravity at bay, but the price for that is turning hydrogen into heavier elements that don’t want to fuse. At the end of a star’s life, there’s not enough fusion going on to resist gravity wanting to crush things. Once the tipping point is reached and gravity wins, things happen *very* quickly. Like the stack of balls in the Galilean Cannon, all the layers of the star go rushing to the star’s core and compacting. Once things can’t compact anymore, they explode outward, resulting in a supernova, and when you consider the sheer amount of mass in a star, that results in a huge momentum transfer. That means that the outer layers gets blasted out at near light speed.
Latest Answers