Remember that scene in Star Trek: Generations, where Malcolm McDowell’s character had access to this giant gun that would stop all fusion processes within a star, causing it to immediately go out? No? Well, umm, he did and uhhh (damn now I gotta explain the whole movie), so umm, let’s just say he was a bad guy trying to put out a bunch of stars that were in his way. He was Captain Kirk’s Dr. No.
Now just so you know, I’m not the physics-nerd-party-pooper-guy that goes to parties telling everyone why warp drive won’t work or that the holodeck is impossible for this or that physics-related reason, but, I’m sorry folks, it turns out things wouldn’t work out quite the way the movie would like. If such a gun did exist, Malcolm McDowell would have to wait around about 6 million years for anything to happen.
I can say that here though, because no matter how much I would wish it otherwise, this blog simply isn’t a party. It could also be argued that any party where the physics of Star Trek is a topic of discussion probably isn’t a babe-fest to begin with, but I digress.
Before I tell you why it would take so long, I have to confess that my title for this post is a little misleading. When I say stopped shining, I mean if the processes that caused the Sun to shine, nuclear fusion, suddenly stopped today, we wouldn’t notice it for another 6 million years. The Sun would still shine during that time.
But that title was way catchier than: If Nuclear Fusion Suddenly Stopped at the Core of the Sun, then blah,blah,blah…
OK, so here goes…
Stars, of which our Sun is one, shine by fusing Hydrogen atoms into Helium, Helium into heavier elements like Carbon, with each set of fusion processes producing heavier elements up to Iron. Iron can’t be fused in stars and so the chain stops there. It isn’t a neat progression for one element to the next, but the basic effect is that lighter elements fuse into the heavier elements and stop at Iron. A star with an Iron core is ready to die.
These fusion processes occur in the core of the star, with a minimum temperature of 5 million degrees to fuse Hydrogen, 100 million degrees to fuse Helium, 1 billion degrees to fuse Carbon and even higher temperatures to fuse heavier elements. When two atoms are fused together to make a heavier element, a large amount of energy in the form of photons of all wavelengths, from radio to x-rays, are emitted.
What’s really remarkable about this however, is that it takes that photon, once it’s released in the core, several million years to reach the surface of the star.
You head off in one direction, get bounced in another direction, then still another, and so on. The problem is that, unlike the person in a subway station, the photons (particles of light) don’t know which way they want to go. They are jostled about in scattering collisions with particles (mostly electrons). It’s like being blindfolded in a crowded subway station. Eventually you will work your way to the door by chance and leave. But how many steps will it take you to go a certain distance?
For photons emitted in the cores of stars, the answer turns out to be millions of years. So, the light we’re seeing from the Sun today, was actually generated several million years (and eight minutes) ago.
Once the photons escape from the surface, it only takes them eight minutes to get to us traveling at the speed of light.
Just thought you might want to know in case you decided to build a gun like that for yourself.