How did the sun and other stars transform matter into energy through nuclear fusion?

Answer 1

The Sun and all of the stars are gigantic spheres of hydrogen and helium, formed from interstellar gases that are left over from the formation of the universe, as well as from the remnants of supernovas. They are so gigantic that their mass compresses the core.

As they condense, they become denser and hotter, and this pressure builds up. At around 10 million degrees Kelvin the core is hot enough for fusion reaction to start.

This fusion reaction involves, on the atomic scale, the fusion of four hydrogen nuclei into one helium nuclei. Since the binding energy (Strong Atomic Force) of helium is much less than that of hydrogen, this fusion also results in the release of energy, which increases the heat level and makes the reaction faster.

On the atomic scale, there is not a lot of energy, but on the grand scale, there is enormous energy, which percolates from the core to the photosphere, released as heat, light, and radiation. The reaction is self modulating, in that as heat goes up, density goes down, with a reduction in fusion rate, and vice versa.

This reaction involves a loss of mass. Mass, per Einstein's famous equation e = mc2 shows that the mass is converted into energy, on a very large scale. Eventually, the Sun and stars will run out of fuel. Various end-of-life scenarios exist, depending on the initial mass of the star. Our Sun is considered relatively small, so it is not going to turn into a supernova, but instead it will turn into a red giant and consume Mercury, Venus, and possible Earth. Don't worry - that is not anticipated to occur for another 4 or 5 billion years. In fact, long before that happens, the Sun's dwindling fuel will cause it to become larger and thus hotter, and it will destroy the Earth's atmosphere - again, that is not anticipated to happen for about another 2 billion years.

Depending on various factors, as the hydrogen fuel is used up, helium fusion accelerates, creating lithium, beryllium, and so on and so forth, all the way up to iron.