[♪♪]
Joe Pesce: So what are
black holes?
There are two main classes
of black hole
so-called stellar
sized black holes
that come from the explosions
of stars-individual stars.
Basically, space has collapsed
in on itself
to a infinitely small size
the so-called singularity.
And because that's so small
but yet contains
the mass of the object
that created it
the gravitational field
is very intense
and so it's so intense
that nothing can escape,
not even light.
And so that's where
the definition
of a black hole comes from.
Black Hole has has a radius
the outside of which is
what is called the event horizon
and its event horizon
can be thought
of the last stable orbit
in essence beyond which a photon
or or an object can escape
but within which the object
of the photon cannot escape
and it falls
into the black hole.
So those are stellar sized
black holes
they have the mass of three,
to five, to 20
or 30 times the mass of the sun.
The black hole
that we're talking about here
is what we call
a supermassive black hole.
We don't know how those formed.
Perhaps they accumulated
smaller black holes
and other material, stars
for example,
and built up mass over time.
But those supermassive
black holes are in the range
of millions to billions of times
the mass of the sun.
So they have a lot of mass
but they're very small.
They don't have the size
a supermassive black hole
that say a billion times
the mass of the Sun its diameter
is small from
an astronomical perspective.
That diameter is about the size
of our solar system.
And so that's big.
From a human perspective
but from
an astronomical perspective
that's it's not big at all.
So these big massive black holes
that have a small spatial scale
are sitting in the middle
of galaxies.
It's a common misconception
that these black holes
will suck us into them.
But you need to be really really
close to the black hole itself
because it's spatially small.
You need to be very close
until you're affected
by its gravitational influence
and then to be sucked into them.
So a black hole sitting in the
middle of our galaxy for example
is you know
it's very distant from us.
Twenty, thirty thousand
light years away
and its mass is there.
And so our solar system feels
that mass as we orbit the galaxy
but we are in no way going to be
sucked into the black hole
that's in the middle
of our Milky Way galaxy.
So we can we can rest easily
at night because of that.
Nonetheless we don't know
what happens to matter
after it falls into a black
hole.
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