So to really get a sense for these 
objects nothing is better than an actual 
tour luckily a virtual tour to a black 
hole. 
Our tour guide is Andy Hamilton of 
Colorado University who has generously 
let us use these beautiful simulations 
he's made. 
So we're, we're er, going to approach 
this 
Little system of stars we got a 60 solar 
mass blue main sequence star with some 
other e smaller stars and orbiting in a 
binary system with this blue star is a 30 
solar mass black hole, which of course we 
can't see and 
30 solar masses tells us that its 
Schwarzschild radius is 30 times the sun 
mass, three kilometers. 
And this is an image of our trajectory. 
We are going to be in free fall, 
so we're going to be accelerated towards 
the system and fall into an unstable 
orbit at, two Schwarzschild radii. 
That is a zero energy orbit, 
so you can actually freely fall without 
any engine power into that unstable 
orbit. 
You don't want to miss, 
because if you miss by a little bit, 
you either could fly, flown back off to 
infinity or fall into the black hole. 
of course since it's virtual, 
we'll manage to survive it either way. 
But let's start by approaching this 
system from a distance and see what the 
effects are of coming close to a black 
hole. 
So, I start the simulation and we are 
falling from a 100 million kilometers. As 
we approach at about a 100 Schwarzschild 
radii, the lensing of the black hole 
produces what is called an Einstein ring. 
The hole, a doughnut-shaped image of the 
blue star, which is formed by light 
lensing and bending all around the black 
hole. 
And as we get nearer we see multiple 
lensed images of all of the stars, 
because remember we are now at The, this 
clip ends at three Schwarzschild radii, 
the last stable orbit. deflection of 
light is significant and we see these 
multiple lensing effects. 
Notice that on the 
bottom, on the horizon itself the 
animator has superimposed this nice red 
grid for us. Of course the actual horizon 
does not have a red grid on it and if it 
did you would not be able to see it. 
But this just tells you where the 
Schwarzschild horizon is, and the 
interesting property is that because of 
the deflection of light note that you can 
see both poles of the horizon. So you can 
see all the way around it because light 
is so greatly deflected. 
anA so that was us at the last stable 
orbit, at three Schwarzschild radii, but 
that is for sissies. We are heading down 
to two Schwarzschild radius orbit. 
We are now orbiting the black hole at two 
Schwarzschild radii. 
We see all of the enhanced lensing 
effects that I was talking about. 
We see multiple images of all of the 
stars, in the cluster. 
forming and disappearing. 
If you want to know the proper time 
period of orbit is about four 
milliseconds. 
first to someone viewing us from far 
away, it's a factor of two. 
Note what a two Schwarzschild radii. 
The gravitational redshift factor is a 
square root of two, 
but there's another square root of two 
because we are moving at about 0.7 times 
the speed of light to maintain this orbit 
at two Schwarzschild radii. 
You can compute both of those things. 
So looking from afar, we would appear to 
be orbiting at every eight milliseconds, 
where in fact we think we're orbiting 
every 4 milliseconds. 
The tidal forces at this point are I 
believe a thou- a 100 times G. 
So your feet are pulling on your head 
with 100 times their weight. You're 
getting a little bit uncomfortable, I 
should think, 
and then these white dots are a probe 
that is being dropped conveniently, 400 
kilometers ahead of us. 
down onto the surface of the black hole 
from rest, 
and as we approach it we see it falling 
down because it's dropped ahead of us in 
orbit and we see it falling down. 
And what we see is A, this probe is a 
sphere and we see this tidal force 
stretching it out till it's no longer 
anything like a sphere. 
And second of all, we see there as it 
would fall, as it approaches the 
Schwarzschild horizon, 
it is reddened and slows down. 
The bit that is closest to the horizon 
appears to stop falling first, 
and eventually, it turns red, and merges 
with the horizon. 
We can't see it because the red shift is 
infinite, even between the Schwarzschild 
horizon and the orbit at two 
Schwarzschild radii where we are. 
And now, 
well this is unstable, but not dangerous 
enough for us. 
We're not here for the tourist version. 
We're going all the way. 
We're going to fire the boosters slow 
ourselves down slightly and land on, well 
not land, but penetrate through the 
surface of the black hole. 
We just cross the horizon, and at the 
point that we cross the horizon within 
about a tenth of a millisecond, we are 
going to be in the, hitting the 
singularity for a 30 solar mass black 
hole. 
The g-forces at the Schwarzschild of 
radii, radius for this 30 solar mass 
black hole are a million g. 
So we have long since been decomposed, 
and as we fall through the horizon, 
we will meet anybody who fell through 
just before us, 
and we have a tenth of a millisecond to 
have a deep conversation with them before 
we hit the singularity and everything 
ends. 
So this was a quick tour of a black hole. 
And you lived to tell.