Don：嗨 米歇尔博士 宇宙初开就产生了元素周期表吗？
Don, you have asked a question that’s related to
what I think is my absolute favorite fact in the universe
and that is that we are made of dead stars
And that’s literally true.
The atoms in our bodies were actually created inside the cause of stars
that then it exploded and died, or unraveled into space.
然后恒星爆炸 死亡 或者解体进入太空
And so your question about the periodic table is very interesting.
Well, what’s the periodic table like
at the beginning of the universe the moment of Big Bang?
Well one thing I can say, it was a lot simpler.
Eh, The Big Bang, when it went off, produced basically three elements.
Almost everything was hydrogen.
There was a little bit of helium,
and a tiny tiny little smattering of lithium as well.
So those three elements were around
just a couple of minutes after the formation of the universe
but nothing else.
And, and that’s actually not a theory.
That’s actually something we can observe.
One of the wonderful things about being an astronomer is,
as you look out into space farther and farther away
the light has taken longer to get to you.
And the farthest we can see is actually back to a time
only about 400,000 years after the Big Bang.
And really, at that time,
there was nothing but very hot hydrogen gas,
and a little bit of helium and lithium as well.
So everything larger than that,
every atom more complex,
had to be formed inside a star.
Over time, our stars, like the sun,
随着时间的推移 恒星 比如说太阳
are pretty good over the life circle of producing things like carbon and oxygen.
They don’t really get much more far off the periodic table than that.
If you want to go any farther than the element iron,
you actually need a very violent explosion,
a supernova explosion
The cores of very massive stars —
by that I mean stars that are
10, 20 maybe as much as 50 times the mass of the sun,
their cores are much hotter,
because the gravity crushes things down,
and temperature goes up many many millions of degrees hotter than inside the sun.
So these stars can actually form bigger and bigger atoms.
The hotter the temperature, the denser the core,
the more you can ram things together
and actually form bigger and bigger atoms over time.
But there’s a very special thing that happens
when you get to the atom iron.
And it’s something you’ve actually heard about but you may never have thought of.
And that when people think about getting energy out of a nuclear reaction
you’ve heard about fusion reactions.
So like a fusion bomb,
actually takes hydrogen, fuses it together to make helium,
and that creates energy.
And that’s a nuclear bomb.
The sun also runs on that particular reaction,
fusing hydrogen together.
But then you also heard that there’s something called fission.
And this is how, say, a uranium bomb would work.
A uranium nucleus has many, many particles inside it
you actually get energy out of breaking it up,
and forming two smaller nuclei
that are actually a bit denser and they hold together better.
And so you get energy out of breaking them apart.
And the element iron is exactly halfway between those two processes.
So you’ve been getting energy by fusing things together until you get to iron.
And iron is the first nucleus
where you don’t get any energy out of fusing it.
From anything bigger now,
you get energy out of ripping apart fission.
So iron is what sets off a supernova explosion.
When a star tries to fuse iron together, it absorbs energy.
And that’s not great for the star.
The core collapses.
And that huge collapse creates this giant wave of heat
and the formation of many, many new elements after that.
So anything heavier than iron has to be created in a supernova explosion.
Now there are some elements heavier still
that even supernova energies don’t really
get up to quite high enough to make.
And this is something we only found out
recently in the last couple of years.
Elements like gold.
Gold is actually a really interesting one.
Platinum are interesting enough.
Bismuth, and all the big things like uraniumand, all of the really large atoms,
they have to be formed by something that seems almost preposterous,
but we have observed this happening
two neutron stars colliding
So neutron stars are the cores of dead stars.
The density of a neutron star
is about a Mount Everest worth of mass in every square centimeter.
So think about crushing Mount Everest into a little cube like that.
The entire star, which is only about 10 miles across,
is actually that density.
And that means you have a tremendous amount of nuclear components —
neutrons, protons really close together.
And two neutron stars collide, and when that happens,
you make all of these very heavy elements up like gold,
and platinum, and uranium, and all the big stuff.
比如金 铂 铀以及所有大元素
And again, this is not something that we just know theoretically.
We actually have observed this happening.
Recently, we observed two neutron stars colliding.
And in that single explosion,
10,000 times the mass of the Earth in gold came out of that explosion.
It was tremendous .
So we definitely know where those atoms come from now,
we observed that happening.
So to recap,
at the beginning of the universe, you had three elements,
mostly hydrogen, a little bit of helium, tiny little bit of lithium.
Now we have the entire periodic table.
And a lot of those are formed in stars like the sun.
Anything past iron has to be
formed much more violently in a supernova explosion
or in the case of very large atoms,
two colliding neutron stars.
And over billions of years, we’ve filled out the periodic table that way.