Welcome back everybody.

So, today we want to talk about black holes which are

some of the most interesting objects that exist in the universe.

There's still many, many, mysteries associated

with the physics of black holes.

But, we have over the years been able to

investigate them, both theoretically and now we're beginning to

get some observational data about them, to be able

to learn some fundamental things about their their properties.

So, first of all let's just remind ourselves why

there might need to be black holes we've seen

that when a star ends its life. It ends it's nuclear production.

And so it has to resort to some

other mechanism to support itself against its own gravity.

Remember that for stars that are on the main

sequence with a mass of eight solar masses or below.

They ended up as white dwarfs where electron degeneracy pressure,

electron quantum mechanical pressure, could support the star forever in some

sense against its own gravity.

For Neutron stars which are stars that are, which is the

end state of stars greater than eight solar masses the neutron star

was even more compact, and it was neutron quantum mechanical pressure,

what we call degeneracy pressure which supported them against their own weight.

But at some point and we don't really know where if

a neutron star forms with another large enough mass, even neutron

degeneracy pressure, even the effect of quantum

mechanics is not going to be able to

support the the, the, the husk, the corpse of the star against its own weight.

And then even that material, that neutron star,

will collapse on itself and what happens then?

Well, according to our understanding of physics, there

is no known force which can halt the

collapse from the point onward and the star

literally, the material that's in the the neutron

star, the material that's left over from the massive stars evolution.

Will collapse to a single geometric point.

Now you may think that's a very strange thing, how can you get two,

three, four, five times the mass of the sun into a point which has

no dimensions, right that's the whole point of a geometric point, it has zero

dimensions, there's no no width or height or breadth and so that seems an absurdity.

And that is actually the problem for understanding,

one of the problems for understanding of black holes is that

you have a tremendous amount of mass that is in a infinitely

small amount of space and what translates into from Einstein's understanding

of space and time, and gravity is that, that is infinite curvature.

The distortion of space-time that occurs around this point now, is is infinity.

And what a scientist called this, there, we have a word for this and we call it

a singularity.

That this point that has infinite density essentially, is a singularity.

And what that really means is it's a place where the equations Einstein's

equations sort of you know roll on their back and their legs wiggle around.

The end of Einstein's equation's applicability.

And say well, okay then what equations should we use?

Well, we know that Einstein's equations are very good for understanding the

sh, the structure of space-time, particularly

it's good for understanding on large scales.