Robert Clayton
Prof. Kudelka
CCI
11 October 2005
The Invisible Vacuums
Roughly speaking, a black hole is a structure of mass that has such a strong
gravitational pull that nothing can escape it, not even light. Every body of mass has en
escape velocity, which is the rate that an object needs to be propelled at in order to escape
an object’s gravity. If you have a bigger object that has more mass, the escape velocity
will be greater. The Earth for instance has an escape velocity of 11.2 kilometers per
second (about 25,000 m.p.h.), however the moon, much smaller has one of only 2.4
kilometers per second (about 5300 m.p.h.). A black hole however has so much mass, that
not even light, which travels at 700 million miles an hour can escape from it’s pull.
A dying star forms a black hole. Once the star (in this stage of the star’s life it is a
red super giant, much larger than our sun) has used up all its fuel, it simply is unable to
support itself against its own gravity. It collapses upon itself and a black hole is formed.
Inside a black hole, the gravity is so strong that any object inside it will be crushed.
The physical end of a black hole is called an ‘event horizon’ it is sphere shaped
and surrounds the black hole. It is possible for objects to cross into the horizon, but
impossible for them to cross out. It is easiest to think of the horizon as a place where the
escape velocity equals the speed if light. Even if something is less than a millimeter away
from the horizon, it can still get away if it has enough force to. Of course the only thing
that would be able to get away that close to the horizon is light, but it is still possible.
However, as soon as an object crosses the horizon, its fate is sealed. Not even light would
be able to escape.
The horizon is a complicated entity. If someone were able to get close enough
without being in danger, they would view it as an unmoving object. Once you get into the
horizon however, you would see that is actually moving outward at the speed of light.
This helps to explain why you can cross into it, but not out.
A black hole is a big object. It is big in two ways, mass and size. There is no limit
to the amount of mass that can be made to form a black hole. Black holes are formed
from the death of a massive star, but the Conservation of Energy law states that no mass
can be created nor destroyed in a reaction, so it is suspected that a black hole will have
the same amount of mass as the star from which it died. Let’s say that the mass of a star
was around 10 times the amount of our sun’s mass (a solar mass), which would be 1031
kilograms. Many scientists believe that black holes also lay at the center of galaxies
(including our own) and those black holes weigh up to a million times the solar mass,
1036 kilograms.
The more mass that a black hole contains is directly proportionate to the radius of
the black hole’s horizon. For example if one black hole weighed five times as much as
another black hole, its radius’s horizon would be five times as big. If a black hole had a
solar mass, it would have a radius of three kilometers. A ten solar mass black hole would
have a radius of thirty kilometers and a thousand solar mass black hole would have a
thousand kilometer radius.
Many people wonder what would happen if they went into a black hole. They
wonder if it would be an instant death or if they would experience the gravity for a while.
Let’s use a black hole that has a million solar mass. If you are far enough away from the
horizon at first, you wouldn’t feel anything. You are being pulled in, but the pull is not
that strong. Everything you are around (your body, your ship and everything in it) is
being pulled the same way at the same rate, so you feel weightless. Eventually, you feel a
tidal pull, which can best be described as this: if your feet were closer than your head (to
the center of the hole) then they would be getting more of a pull, leaving you with a
stretched feeling.
Your vision is fine; you see some objects that are slightly distorted because the
hole’s gravity bends light. Even as you cross the horizon, you can still see out. This is
because there is still light coming into the hole. No one can see into the hole because the
light is not strong enough to get out. However, you don’t really have time to think about
that kind of stuff, because seven seconds after crossing the horizon, the tidal pull gets so
strong on your body and ship that it rips your bodies apart.
If someone is watching you fall into a black hole, they would get quite a different
view. The closer and closer you get to the horizon, the slow and slower they will see you
move. This is because it is taking the light longer to escape the pull because it is so close
to the horizon. The person watching will never see you actually cross the horizon, which
is why the holes were originally called frozen stars, because the object seemed to ‘freeze’
just before it crossed the horizon. The light you emit will never reach anyone because it
will be suspended at the horizon. I mentioned earlier that the escape velocity at the
horizon is the speed of light. The light is not strong enough to fully get out, but not weak
enough to get sucked in. You have long since passed into the horizon and dead by now,
but the light telling her that will never reach her.
Another common question that people have is that since a black hole is the
remnants of a dead star, will the sun eventually become a black hole? Scientists don’t
think the sun will follow that path. They think that the sun will just become a dead white
dwarf star. Before either of these happen however, the sun will become a super giant,
which means life on Earth wouldn’t be possible. The sun will become so big that it will
engulf Mercury and Venus, making Earth the closest planet to the sun. The water will all
evaporate and the atmosphere will crumble. This all isn’t supposed to happen for another
five to eight billion years. So, there is nothing to worry about now.