How does a star's composition change throughout it's life?

Question

I want to know how a star's composition changes throughout it's life. I know that it starts out as just dust and particles, but what are they made of. And then it becomes a star, what is it made of in its earlier years, and how does it change. I know that it fuses hydrogen to make heluim, and that's it keeps on shining, but what happens when all the hydrogen is gone? does it keep on fusing helium to make berylium?

if you could, i would like some websites also when you put in your answer.

Answer 1

Sounds like you've already got a good understanding of stellar evolution. The materials the star forms from *must* consist of an abundance of hydrogen gas or a new star can't get started; *all* stars begin by fusing hydrogen into helium. Once the hydrogen "fuel" is exhausted things get more complex. Take a look at this website for a very good detail of our sun's evolution ==>http://www.astronomy.ohio-state.edu/~...

Answer 2

Stars are born from huge clouds of hydrogen that are compressed by their own gravity to the point when a thermonuclear reaction starts at the core of that system.

After millions to billions of years, depending on the initial mass of the star, the continuous fusion of hydrogen into helium will cause a build-up of helium in the core. The accumulation of helium, which is denser than hydrogen, in the core causes gravitational self-compression and a gradual increase in the rate of fusion. Higher temperatures must be attained to resist this increase in gravitational compression and to maintain a steady state.

Eventually, the core exhausts its supply of hydrogen, and without the outward pressure generated by the fusion of hydrogen to counteract the force of gravity, it contracts until either electron degeneracy becomes sufficient to oppose gravity, or the core becomes hot enough (around 100 megakelvins) for helium fusion to begin. Which of these happens first depends upon the star's mass.

After the star has consumed the helium at the core, fusion continues in a shell around a hot core of carbon and oxygen. In a massive star, electron degeneracy pressure is insufficient to halt collapse by itself, so as each major element is consumed in the center, progressively heavier elements ignite, temporarily halting collapse.

Above a certain mass (estimated at approximately 2.5 solar masses, within a star originally of around 10 solar masses), the core will reach the temperature (approximately 1.1 gigakelvins) at which neon partially breaks down to form oxygen and helium, the latter of which immediately fuses with some of the remaining neon to form magnesium; then oxygen fuses to form sulfur, silicon, and smaller amounts of other elements.

After a star has burned out its fuel supply, it becomes either a white dwarf, a neutron star or a black hole.

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