Helium Ignition in Stars

When I first began learning about stars, I expected them to be violent and chaotic places. And to an extent, they certainly are.

Pressures are unbelievably high in their cores—high enough to smash protons together, and this is no small feat. And near their surfaces, magnetic field loops twist and tangle and a number of eruptions disrupt satellite function on Earth from time to time.

Beyond the obvious, though, stars are actually surprisingly…peaceful.

While stable, they only produce enough energy to sustain their own mass. Their way of maintaining homeostasis is beautiful in its simplicity.

But this can’t last forever. Eventually, stars exhaust their hydrogen fuel. Their cores begin to contract and their outer envelope expands to enormous proportions.

What’s next for a star—and why?

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What Happens in an Expanding Star’s Core?

Depending on their mass, stars can remain stable for millions and even billions of years. The most massive stars live for “only” about 10 million years, but models predict that the least massive live for much longer—longer than cosmologists believe the universe has existed.

As long as stars are stable, they exist on the “main sequence.” That’s just a fancy word for the best balance between temperature and mass. For a while now, we’ve been exploring the main sequence in depth, and I’ve shown you how stars eventually lose stability and “leave” the main sequence.

As stars exhaust their fuel, their internal structures change drastically. Their cores contract, but their outer layers are forced to expand, and they become giants. You’d think the next thing we’d cover would be what happens to these giant stars, right?

Well…not quite! At this point, something downright weird is going on in their cores, and it’s well worth a closer look…

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