The Cosmic Classroom - Evolution of High Mass Stars

Uploaded by vmargoniner on 30.10.2009

Hi there. Welcome back to
the Cosmic Classroom. Now it's time to talk
about the life of high mass stars.
And I know you want to know about them
because they end as black holes and that's
something you're really curious about.
I know that. So let's get to it.
So high mass stars start there lives just
like low mass stars. They go through the
same process of being a Main Sequence
star, fusing Hydrogen into Helium in its core,
and then started to fuse Helium in the
core and then, and then when it gets to
Carbon actually the star has enough
mass that indeed it does get hot enough
in that core for you to fuse Carbon into heavier
elements and heavier and heavier and heavier.
So the beginning I don't need to repeat, the
beginning go back to life of low mass stars.
And, but if the star has enough mass, has more
than eight times the mass of the sun it will
be able to fuse heavier and heavier elements
all the way to Iron. So let's see here, we have.
Can we take? Yeah, thank you. So high mass stars, so
same stage as high mass stars continue this process
as you can see here. Until eventually what
we have is a star, now looks more like
an onion than a star. It has shells and
shells and shells fusing different things.
Alright? So the very core of this,
eventually at the very core of this star
what you have is Iron. Iron won't be able to
fuse into anything. Right?
And around it you have Silicon,and
around that you have Magnesium, and around
that you have Neon, and Oxygen, and Carbon,
and Helium, and Hydrogen. So you have a lot
of fusion happening. You can only imagine
that if you're fusing all of those elements
at the same time this star is huge.
Right? It is generating a large
amount of energy. So this star becomes
a super giant. Alright?
But as the low mass stars, eventually they
run out of fuel because they can't fuse Iron
and everything else becomes too cold.
Alright? And it can't be fused.
So what's going to happen to it?
It's interesting to notice that stars that are very
massive they actually go through all of this
processes much faster than stars at are low
mass like our sun. Think about it like someone
that's biking and saving its energy and go slowly and
and keeps going and going and going and going
and never has to refuel. And then think about
the Hummer that you need to keep refuel,
so it has a lot of fuel, but it runs out of it.
Right? With a small star just
uses it so slowly that it lasts for a very long time.
So high mass stars actually live much less, die much
younger than than than a lower mass star.
So you have this multiple shell burning, you probably
remember this plot from before,showing that, that
you can only get energy out of the fusion, of
elements lighter, LIGHTER than Iron. When you get to Iron,
what happens is,first of all the Iron will
build in the core, until the degeneracy pressure
of this Iron cannot hold it anymore, cannot
hold all this gravity. Imagine it's
it's a huge force. Right?
There is, there's this huge star all
around this nucleus, and this core of Iron
that's becoming smaller and smaller and
denser and denser. Eventually not even
the degeneracy pressure is able to stop the
atoms to, to come and combine with each other.
So what happens is that at this pressure a Proton
combines with an Electron and forms a Neutron.
You lose any information about
what kind of elements were there before.
You don't know that it was, if it was Iron
or what was it because they,as you
see here Protons will combine with an Electron
and form a Neutron. Ok?
So you have a huge ball of Neutron, that's
what you have. You have a huge
ball of Neutron. When this huge ball of
Neutron collapses, it may do one of two things.
It will explode in a supernova,and then it
may do one of two things. It may either keep
this Neutron star, this core that's made only of Neutrons.
To give an idea of how dense this is.
And I'll talk more about Neutron stars in some other time
because they're fascinating. But just to give you a
glimpse, a Neutron star has a density such that
if you just get the volume of your thumb,imagine
fitting every person in the surface of the earth
and squeezing them here. At the surface of my thumb.
At my thumb. Sorry not at the surface.
Just squeeze in the volume of my thumb.
Everybody, the six billion people at the
surface of the earth. That's how dense it
is in a Neutron star. It's mind-boggling isn't it?
That's what is is. And if the explosion
depending on the mass, if they, if the explosion
is big enough, you end up with a black hole.
So, so when a supernova explodes you either
have at the end a black hole or a Neutron star.
Two fascinating objects that I love to talk to you about.
And it will come just wait because it will come.
Alright? So that's how high mass
stars die with a big supernova explosion.
I hope that helped and I'll see you next time.