Black Holes
As an object's mass increases,
so too does its impact on space time and as a result its gravitational
pull is stronger ( See 'Brian's guide to Einstein
and Gravity' for more info ). As mentioned earlier, smaller stars
( under 1.4 solar masses ) have the peaceful fate of becoming a white dwarf
at the end of their lives. Slightly larger stars ( between 1.4 and
3 solar masses ) become neutron stars. That leaves MASSIVE stars.
These stars have the unfortunate fate of becoming a black hole.
One of the theories relating to black holes is the Schwarzschild Radius.
The radius is equivalent to r=GM/c². Where r
is equal to the radius, G is Newton's constant of universal
gravitation, M is the mass of the star and c is the speed
of light. To simplify things, we will use the equation r=3M
which provides about the same solution ( in kilometers, not miles as was
intended originally ). Inside the Schwarzschild Radius, space time
becomes distorted and the gravity is incredibly strong. According
to this theory, anything within the radius is unable to escape, even light.
The Schwarzschild radius, then, for the sun would be around 3 kilometers
and 3 million kilometers for a million solar masses. Therefore if
we were to be 3 kilometers away from the centre of the sun, the effect
it has on us at that distance would be the same as a black hole's.
A black hole then, must have the distance from its centre to its surface
larger or equal to about 3 times its mass. From that, you can imagine
how dense a black hole must be to achieve the Schwarzschild Radius.
In order for a star to achieve black holeness, it must be dense enough
to reach the Schwarzschild Radius and for such a thing to happen, the beginning
star must have an incredible mass for its gravity to have an advantage
over the remaining nuclei in its core.
The reason for the name 'black hole' is mainly because no light is able
to escape from it because the escape velocity
for a black hole is so high. Regardless of what many people think,
light is also affected by gravity as is everything in the universe.
However, light does not slow down when being pulled by gravity like a stone
thrown into the air, but rather its wavelength
increases. So if visible light were to be traveling away from the
centre of a black hole its wavelength would increase to become infrared
light, then microwaves, then radio waves and eventually it would cease
to exist. And that is how a black hole traps light.
The point in a black hole where everything is pulled towards is called
the singularity.
This point in the black hole is thought to be infinitely dense and as a
result has an infinite gravitational pull. If you were to be sucked
into a black hole the singularity is where you would end up and be crushed
by the gravity inside it. This singularity causes such a large bend
in space time that it creates an event horizon
- which acts as the surface of the black hole - whose distance from the
singularity is equal to the Schwarzschild Radius of the black hole.
The horizon is where the escape velocity
starts to become greater than the speed of light and since nothing is faster
than light, anything that enters the horizon is unable to escape.
This massive bend in space time acts as an attractive funnel to the singularity
pulling anything within range towards the singularity. Past the horizon,
space and time are so distorted that they practically switch places.
So the distance you are traveling in the normal world would not be distance
anymore but rather a period of time. Therefore, getting from point
A to point B would instead be getting from time A to time B. The
only difference is, there is no way to avoid it. If you tried to
stop from getting to point B it would be almost impossible unless you could
either travel a LOT faster than light or go back in time since inside the
horizon, avoiding point B is like avoiding the next minute in your life.
Now, your probably wondering, after all this, what would happen if you
fell into a black hole. That takes us to the next subject 'A
Trip to Oblivion.'