Translator: Theresa Ranft Reviewer: Leonardo Silva
I have a slight problem, but the show's going on.
My blood's red.
Is Viennese blood red?
(Laughter)
I suspect it is.
Why is blood red?
Does anybody know? Can you tell me?
(Audience) It's iron.
It's iron, yes.
It's iron in the hemoglobin, in our bloodstream,
that makes the blood red.
Iron is one of the chemical elements,
and I'm going to talk about that in a moment.
But, just first ...
(Laughter)
... tomato ketchup.
We'll hear more about tomatoes later.
(Laughter) (Applause)
Back to the chemical elements and iron.
It is, indeed, one of the chemical elements,
and even if you're not a chemist, you probably know of some others.
An answer given by a student in an exam.
[H2O is hot water and CO2 is cold water.]
(Laughter)
So, you know what H2O is?
(Audience) Water. Jocelyn Burnell: Water. CO2?
(Audience) Carbon dioxide. JB: Carbon dioxide.
So, we've got here another three chemical elements:
hydrogen, oxygen, and carbon.
And while we're dealing with student exam questions,
here's another one about water:
Water is composed of two gins ...
[Water is composed of two gins, Oxygin and Hydrogin.]
[Oxygin is pure gin. Hydrogin is water and gin.]
(Laughter)
These answers come from the United States of America, but ...
(Laughter) (Applause)
It's a wonderful resource of all sorts of amazing things that come true.
Maybe some of you recall seeing a diagram like this
in school chemistry laboratories.
You can see it in other places, too,
even these days on tea towels, mugs, bags, pens.
It's a tabulation of the 100 plus chemical elements that we know about.
In Oxford, where I come from,
we have it on taxis and buses, as well -
but that's Oxford.
(Laughter)
Now, in our bodies, there's clearly iron in the bloodstream,
there's also hydrogen and oxygen because we're two-thirds water.
There's carbon in our tissues, calcium in our bones.
I'm going to focus on the iron because this is a short talk.
Where did that iron, and, indeed, where did those other things come from?
How did it get into our bodies?
It's not in the air ... much.
It's come through what we've eaten: plants and animals.
How did the iron get into the plants and animals?
Well, it came from the earth.
How did it get into the earth?
Where did it come from before that?
What I am going to be telling you about
is how the stars have created the chemical elements -
the key ingredients of life: oxygen, carbon, calcium, iron -
with particular emphasis on the iron.
Stars are formed in some of the dark spots of the galaxy,
the dark patches.
There are particles of gas and dust milling around,
by chance as a little knot,
it's got extra gravity, pulls in some more,
puts up the gravity, pulls in more.
And over some millions of years,
this little knot grows into what's going to be a full-blown star.
When the temperature in the middle of this lump
reaches about 10 million degrees,
nuclear reactions start,
and, in particular, a nuclear reaction of hydrogen being converted to helium.
And there's some energy to spare, and it comes out of starlight.
Our sun's busy doing that:
our sun is burning about 600 million tons of hydrogen every second.
It's done that for 5 billion years.
It'll do it for about another 5 billion years.
And shortly after that, it will end, and it's actually no use for this story.
(Laughter)
We have to focus on a very small minority of stars,
the extremely massive ones,
10, 20, 30 times the size of our sun.
Examples of these that you might know:
the Pleiades - which is in the winter sky near the constellation of Orion,
and Betelgeuse -
which is the reddish star, top left in the constellation of Orion.
These big stars not only convert hydrogen to helium,
but then the helium to carbon,
and work their way across the periodic table
till they end up with iron in the center of the core.
And this is the first place that we have iron in the universe -
in the cores of some stars.
Not very useful to us if it's in the cores of stars.
But star death, dramatic star death, comes to the rescue.
A pair of photographs here: a "before" and an "after."
We're looking at a southern hemisphere object
called the Large Magellanic Cloud.
It's a small galaxy, external to ours, but quite nearby.
We're seeing up top left a glowing mass of gas,
quite a lot of pink hydrogen gas,
millions of little stars,
and one of them, bottom right, picked out with an arrow.
For those of you who are not astrophysicists,
the arrow's added after the photo's taken.
(Laughter)
But, this inconspicuous star that we had to pick out with an arrow
becomes this,
and you don't need an arrow to see that thing in the bottom right.
The star has exploded catastrophically.
It was one of these big stars
like the ones in the Pleiades, or Betelgeuse.
It's gone all the way through the various chemical elements.
It's got this range of onion shells with iron in the middle
and the other chemical elements outside it,
and it has exploded.
The physics of the explosion is quite complicated,
so I'm not going to go into the details of that,
but it is a catastrophic explosion.
We used to assume it was totally catastrophic.
We now know that the pulsars that Vlad mentioned in his introduction
are formed from the cores of these exploding stars.
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.
(Laughter)
The female ones are utterly nuts!
And I'm just about to prove it!
(Applause)
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!
(Laughter)
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.
(Laughter)
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!
(Laughter)
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.
(Laughter)
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.
But that's broadly what has happened.
So we who eat the plants and the animals that absorb elements from the earth,
we are made of the same stuff as the earth,
and the earth is made of the same stuff as the sun,
which is made up of the rest of the galaxy.
So, iron was created in those very massive stars,
ones that went through lots of nuclear reactions.
And that iron was made available
by the catastrophic death of those big stars.
So there's life and death already.
If it wasn't for those stars, particularly the ones that had died,
we would not be here.
And we're intimately and ultimately
children of the stars,
to such an extent that, actually,
we are stars.
Thank you.
(Applause)