But 95% of the star is skooshed out into space, which means that being fanned out across space are useful chemical elements that were inside the star: oxygen, calcium, carbon, iron, spread out, made available by the catastrophic terminal explosion of this particular star.
Now, getting from there to us is quite a long story, and I’m going to do this bit by mime. You’ve probably got some sense that physics professors have a slightly dubious reputation. The female ones are utterly nuts! And I’m just about to prove it.
So, this stage is the Milky Way – our galaxy, and this is a story that involves all the Milky Way. Over here in the Milky Way is one of these dark clouds where stars sometimes form, particles of gas, molecules, dust milling around.
By chance, there’s a little knot, it has extra gravity, it pulls in some more bits of dust and gas, puts up the mass, puts up the gravity, pulls in some more bits.
To save time, folks, this is going to be one of these very massive stars, otherwise we’re here for a long time. So, this gradually grows, gradually grows. And at the point when it’s grown so much that the temperature in the middle has reached about 10 million degrees, it starts its sequence of nuclear reactions, and it burns, converts hydrogen to helium. Brrrr!
Then it starts to run out of hydrogen in its core. So it starts converting helium to carbon. Brrrr! That doesn’t last as long.
Then it runs out of helium in its core, so it converts carbon to oxygen, oxygen. Brrr! Brr! Brr! Brr! Boom! And millions and millions and millions of tons of stuff, gas, fan out from this explosion site in one part of our Milky Way.
It percolates, slowly, but we’ve got eons, there’s no rush. It can travel, and it does travel, gradually, in all directions, but we’re interested in this bit. And some comes over here to where there is another of these dark clouds with particles of gas and dust milling around.
And some of the material from that distant explosion finds its way over here, and that material is rich in carbon and calcium and iron and oxygen, and so on. So it joins this cloud, and by chance a little knot forms, it’s got extra gravity, pulls in some more particles, puts up the mass, puts up the gravity, pulls in some more particles, puts up the mass, puts up the gravity, and over a million years, 10 million years, it grows and grows and grows.
And once again, I have to crave your indulgence, could this also be one of these big stars?– otherwise we’re here all night. So this big star grows, and the nuclear reactions start, and it burns, converts hydrogen to helium. Brrrr! Runs out of hydrogen, burns helium. Brrrr! Runs out of helium, burns carbon. Brrr! Brr! Brr! Brr! Boom!
Now, you know the next bit of the story.
Millions and millions and millions of tons of stuff fan out across space, and some of it makes its way over here to another dark part of the galaxy – the Milky Way – where there’s a star beginning to form. The material that comes from there is doubly enriched in carbon and calcium and iron, and so on, because of the stuff that that star generated, plus the stuff it got from that star, as well.
So, what’s arriving here is double dose carbon, calcium, iron, and so on. And here in this cloud, a star called the Sun is forming, and it’s made from the stuff that happens to be in this patch of the galaxy, plus the stuff that’s come from that star, plus the stuff that’s come direct from there, and maybe from some other exploding stars, as well.
Our sun is a third-generation star. Our star is a late-forming star, and it has to be or we wouldn’t be here. We can only exist close to a young star that’s been enriched by previous solar cycles. So, the sun forms, some of the material is left over. You’ve perhaps seen pictures of the planet Saturn with its rings around it. This is a giant version of that.
So you’ve got a sun and some of the debris in a giant ring around it. Let’s focus on the debris – little bits going around. Little bits occasionally collide with other bits, and they go around and collide with other bits and go around.
And ultimately, you end up with planets and the ring, the rest of the ring has disappeared. The planets are made of the same stuff as the sun, which, you remember, is made of the stuff that was here, plus stuff from there, plus stuff from there.
It makes eight planets, not Pluto. Pluto was grabbed later. You can think of Pluto as an adopted child, if you wish. The rest are birth children. So, these planets are basically made of the same stuff as the sun, which is made up of stuff that was here, plus debris from exploding stars actually all over our galaxy.
It’s not that we can say, “It was that one and that one.” It’s that one and that one and that one and that one and that one and that one and that one and that one – doubly enriched with all these useful chemical elements.
And the planets, likewise, are of the same stuff. There has been some change in that the planets closest to the sun got hot, and the material that most easily evaporates has boiled off. Further out, you can see the original composition rather better.