Supernova (Supernovae)

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Supernova (Supernovae)

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Where we left off in the last video, we had a mature,
massive star, a star that had started forming a
core of iron and it has enormous inward pressure on this core
because as we form heavier and heavier elements in the core,
the core gets denser and denser, and so we keep fusing more and more elements
into it, and so this core becomes more and more massive, more and more dense,
squeezing in on itself, and so. . . It's not fusing! That is not exothermic anymore!
If iron were to fuse, it would not even be an exothermic process!
It would require energy! So it wouldn't be even something that could help
to fend off this squeezing, this increasing density of the core,
so we have this iron here, and it just gets more and more massive,
more and more dense, and so at some mass, already a reasonably high mass,
the only thing that's keeping this from just completely collapsing
is what we call Electron Degeneracy Pressure.
Let me write this here. . .
and all this means is we have all of these iron atoms
really close to each other, and the only thing
that keeps it from collapsing altogether at this earlier stage is that
you have these electrons and these are being squeezed together
we're talking about unbelievably dense states of matter.
And electron degeneracy pressure is essentially saying that
all these electrons don't want to be into the same place
at the same time. I won't go into the quantum mechanics of it,
but they cannot be squeezed into each other any more!
So that, at least temporarily, holds this thing from collapsing even further.
And in the case of a less massive star, in the case of a white dwarf,
that's actually how a white dwarf maintains its shape!
Because of the electron degeneracy pressure!
But as this iron core gets even more massive, even more dense,
and we get more gravitational pressure, so this is our core now,
eventually even the electron degeneracy. . . I guess we could call it
force, or pressure, this outward pressure, this thing that keeps it from collapsing,
even that gives in! And then we have something called electron capture!
Which is essentially the electrons get captured by protons in the nucleus!
They start collapsing into the nucleus!
It's kind of the opposite of beta negative decay, where you have
the electrons getting captured, and protons getting turned into neutrons,
you have neutrinos being released, but you can imagine an enormous
amount of energy is also being released! So this is kind of a temporary (state?)
and then all of a sudden, this collapses even more!
Until all you have, and all the protons are turning into neutrons, because they're capturing electrons!
So then you. . . What you eventually have is this entire core is collapsing
into a dense ball of neutrons. You can kind of view them as one
really really really massive atom, because it's just
a dense ball of neutrons. And at the same time, when this collapse happens,
you have an enormous amount of energy being released in the form of neutrinos!
Did I say that neutrons are being released?
No, no no. The electrons are being captured by the protons,
protons turning into neutrons, this dense ball of neutrons right here,
and in the process neutrinos get released!
These fundamental particles, we won't go into the details here,
but this enormous amount of energy. . . And this is actually is not really really well understood,
of all of the dynamics here, because at the same time that this iron core is undergoing
through this first it pauses due to the electron degeneracy pressure, and then
it finally gives in because it's so massive, and then it collapses into this dense ball of neutrons,
but when it does all of this energy and it's not clear how - because it would have to be
a lot of energy,- because remember, this is a massive star,
so you have a lot of mass in this area over here,
but it's so much energy that that it causes the rest of the star to explode outward!
in an unbelievably bright, or energetic, explosion.
And that's called a supernova.
And the reason why it's called nova, it comes from
(I believe, I'm not an expert here) Latin for new!
and the first time people observed a nova, they thought it was a new star!
because something they didn't see before, all of a sudden,it looked like a star had appeared!
because maybe it wasn't bright enough for us to observe it before, but when the nova
occurred, it did become bright enough, it comes from the idea of new!
But a supernova is when you have a pretty massive star, and its core is collapsing,
and the energy is being released to explode the rest of the star out at unbelievable velocities.
and just to fathom the amount of energy that is being released in a supernova,
it can temporarily outshine an entire galaxy! And in a galaxy we're talking about
hundreds of billions of stars! Or another way to think about it, in that very short period of time,
it can release as much energy as the sun will in its entire lifetime!
So these are unbelievably energetic events. And so you actually have the material that's not in the core
being shot out of the star at appreciable percentages of the actual speed of light!
So we're talking about things being shot out at up to 10% of the speed of light!
That's 30,000 kilometers per SECOND! That's almost circumnavigating the earth every SECOND!
So that's unbelievably energetic events that we're talking about here.
And so if the star, if the original star, (these are rough estimates, people don't have a hard limit here)
is 9-20 times the mass of the Sun, then it will supernova, and the core will turn into what is called
a neutron star. Which you can imagine, is just this dense ball of neutrons.
And just to give you a sense of it, it'll be something about
maybe 2 times the mass of the Sun, give or take, 1.5 - 3 times the mass of the Sun.
In a volume that has a diameter on the order of tens of kilometers!
So roughly the diameter of a city! So this is unbelievably dense.
And we know how much larger the Sun is relative to the Earth,
and we know how much larger the Earth is relative to a city, but this is something more massive
than the sun being squeezed into the size of a city. So unbelievably dense.
If the original star is even more massive, if it's more than 20 times the Sun,
Then even the neutron degeneracy pressure will give up and it will turn into a black hole.
And that's - I could go into many of the details on that.
And that's actually an open area of research still, on exactly what's going on inside of a black hole.
But then it turns into a black hole, where essentially all of the mass gets condensed into
an infinitely small and dense point, so something unbelievably hard to imagine.
And just to give you a sense of it, this will be more mass
than even three times the mass of the sun. So we're talking about an incredibly high amount of mass.
So just to visualize things, here's a remnant of a supernova,
this is the Crab Nebula, and it's about 6500 light years away.
So it's still, from a galactic sense if you think of our galaxy as being 100,000 light years
in diameter, it's still not too far from us on those scales.
but it's an enormous distance. the closest star to us is 4 light years away,
and it would take Voyager traveling at 60,000 kilometers/hour
80,000 years to get there.
So this is a very - that's only 4 light years, this is 6,500 light years,
but this supernova is believed to have happened 1,000 years ago, right at the center,
and so at the center here, we should have a neutron star,
and this cloud, this shock wave that you see here, this is the material traveling outwards
from that supernova, over 1,000 years. The diameter of this sphere of material is 6 light years.
So this is an enormously big shock wave cloud. And we believe that our solar system
started to condense because of a shock wave created by a supernova relatively near to us.
And just to enter another question that was probably jumping up in the last video,
And this is still not really well understood. We talk about how elements up to iron, or maybe nickel,
can be formed inside of the cores of massive stars.
So you can imagine, when the star explodes, a lot of that material is released into the universe.
And so that's why we have a lot of these materials in our own bodies.
In fact, we could not exist if these heavier elements were not formed inside of the cores
of primitive stars, stars that have supernovaed a long time ago.
Now, the question is how do these heavier elements form?
How do we get all of this other stuff on the periodic table?
How do we get all these other heavier elements?
And they're formed during the supernova itself.
It's so energetic, you have all sorts of particles streaming out, and streaming in,
streaming out because of the force of the shock wave,
streaming in because of the gravity.
But you have a mish-mash of elements forming, and that's actually where you have
your heavier elements forming.
And because (and I'll talk more about this in future videos) all of the uranium on Earth right now
must have been formed in some type of a supernova explosion
(or at least, based on our current understanding). And it looks to be about 4.6 billion years old.
So, given that it looks to be about 4.6 billion years old, based on how fast it's decayed,
(and I'll do a whole video on that), that's why we think that our solar system was first formed from some type
of supernova explosion. Because that uranium would have been formed right at about
the birth of our solar system. Anyway, hopefully you found that interesting,
there's a fascinating picture, and if you go to Wikipedia and look up the Crab Nebula,
keep clicking on the image and eventually you'll get a zoomed-in picture, and that's just
even more mind-blowing, because you can see all the intricacy in the actual photo.