The sun and all the stars are powered by thermonuclear fusion — the same process that causes hydrogen bombs to explode. Why the sun doesn’t explode? If the sun is hydrogen bombs exploding, then why doesn’t the sun explode?
When you say the sun is hydrogen bombs exploding you’re talking about thermonuclear fusion — the process that powers the sun and stars — and that scientists in the last century harnessed to make weapons. When a hydrogen bomb goes off, it vaporizes in an intense blast of pure heat and light. A similar process is taking place deep inside the sun . . .
But the sun doesn’t explode because the fusion reactions in its core never become a “runaway” reaction in which everything goes off at once. Instead, the sun is in equilibrium, or balance, between two opposing forces. One force pushes outward — that’s the central nuclear fusion trying to expand the sun, or explode it if you will. The other force is that of the sun’s own gravity, which pushes down and contain the explosion.
You might think of the sun not as a bomb, but as a pot of water on the stove. The flame under the pot is the sun’s burning core. From that core, energy moves outward by convection — so that the outer layers of the sun are like the top of the pot — at a rolling boil.
The boiling pot model is a little bit off. Radiation is a lot more important in the Sun and conduction is a lot more important in the water. To refine the model a little bit, make the pot one of those clear glass Corningware pots and put it on an electric burner. When you look down and see the red of the burner through the water, that’s the radiating energy.
I should admit that when astronomers talk about how stars hold together, they don’t usually talk about explosions and downward pressure. They talk about the power generated at the star’s core pushing outwards balanced by the gravity of the upper layers. The natural tendency for a big ball of gas is to collapse, but once the center gets to a certain density it ignites.
The star keep collapsing until the inward and outward forces balance.The Sun, by the way, never will explode, but some stars do. It isn’t, as you might expect, the small stars without enough gravity to hold together; it’s the biggest stars.
That’s because the extra pressure from all the extra gas gets the center hot enough to allow later stages in the stars’ life-cycles. Eventually it gets to a point where a huge amount of energy is created all at once which is enough to overcome all of the gravity and explode in a supernova.