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Tyrel Mortensen
Physics 1010 - 048
What do you get when you find nothing? How would a point containing infinite gravity affect your
everyday life if you got too close? There are things in this Universe that could completely remove our
planet and all of its life from existence very quickly, but how common are they? The answer to these
questions and so many others can be found through the study of black holes.
Black holes are a massive object, formed by the gravitational collapse of a star exploding as a supernova,
whose gravitational field is so intense that no electromagnetic radiation can escape. A black hole gets
its power from gravity. If you compare Earth’s mass and gravity to a black hole, you would have to
condense the entire Earth into something about the size of a golf ball. This golf ball sized planet would
still have the same mass and gravity as Earth does right now. This gravity is so strong that once anything
gets too close, it’s lost to the black hole.
If a black hole were to find its way into our solar system it could throw all the planets off their orbits. It
could whip moons and asteroids around and cause them to crash into other planets including Earth. On
top of all that our atmosphere would be swallowed by the black hole, and eventually the planet itself.
Black holes use their immense gravity to suck in anything that gets close to them, including light. This is
why black holes cannot be seen and are referred to as black holes.
In the beginning of the Universe it is thought that after the big bang there were a lot of areas with
condensed gases that eventually formed stars. Most of these stars were super massive and burned very
hot and fast. They lived out their lives and eventually turned into small black holes. These black holes
then merged to make bigger and stronger black holes drawing in more and more. New stars formed
from the all the new thick gas being pulled in by these black holes, starting galaxies. From all the
particles flying around the black hole at incredible speeds, things start to get very hot, and at some point
there is no place left for all the excess hot gasses to go, but out. These jets of energy produced from this
lack of space are so powerful they can be 20 times wider than our own solar system, and expel out the
equivalence of 10 Earths a minute. These are called Quasars; they get rid of all the excess gasses in the
galaxy and the whole system stops growing. Scientists believe that at the center of every galaxy is a
black hole. But how do black holes form?
Black holes are formed from dying stars. While most are small, about 20 miles wide, we have
discovered super massive black holes. These super massive black holes can be the same size as our
entire solar system and one can even be found at the center of the Milky Way.
A star is like a giant nuclear fusion reactor, pushing energy outward from its core. At the same time
gravity is pulling everything back towards the core. The star remains stable as long as both forces equal
each other and cancel out, but once the star starts to lose fuel to burn and create energy to maintain
the balance, gravity starts to win. As soon as the balance is shifted gravity takes control and in a
millisecond the core of the star is shrunk to a fraction of the size.
The star then consumes itself from the inside very quickly. So quickly that it cannot keep up with all that
it is drawing in and has a ‘small hiccup.’ This is known as a gamma ray burst, which is a huge explosion
that produces 100 times more energy in its very short life than our Sun will produce in its entire life.
These two jets of energy travel through our Universe frying anything they come into contact with, one
could instantly vaporize our entire planet! Gamma ray bursts are one way scientists have to discover
the locations of newly formed black holes.
Now that the black hole has formed and affected everything in the Universe around it, it doesn’t stop
playing a role in the way everything around it works. It will continue to draw in gasses as well as
planets, moons, and anything else that is close enough to be affected by its gravity. However, there is a
point where close becomes too close, a place where once crossed nothing can escape. This invisible,
point of no return, line drawn around the black hole is known as the event horizon. This is a place
where not even the fastest known thing in this Universe can escape and that thing is light. The closer
you get to the black hole, the harder it is to get away.
The event horizon gets its name because it separates space into 2 regions. While there is no physical
surface for the event horizon, meaning you wouldn’t know when you passed the line if you fell through
it, it is a very real place. This is the point where nothing can escape. Any light from inside the black hole
would not have enough speed to escape the gravity of the black hole, and would be pulled back towards
the black holes center. Since there is nothing that can move faster than the speed of light and not even
light can escape the black holes pull of gravity, it is easy to see why nothing can escape a black hole once
it has crossed the event horizon.
As you get closer to a black hole the powerful gravity starts to have an effect on more than just objects.
Reality starts to break down, and time will appear to stand still once an object reaches the event
horizon. This is because time is relative and affected by gravity the same as our weight is. It is said that
an outside observer can never witness an object cross the event horizon, but from the objects stand
point everything seems to be going as normal. This is because the objects time would be moving
infinitely slowly compared to the outside observers. This phenomenon and the fact that nothing can
ever go from one side to the other of a black hole is why they have been called ‘the edge of space and
the end of time.’
The gravity is also so strong that if you fell into a black hole you would experience what scientists call
spaghettification. This is because the gravity would be pulling on your feet more than your head.
Assuming you fell in feet first. This would cause your feet to be pulled with more intensity than your
head and stretching you out, looking like a long spaghetti noodle.
If you were somehow able to survive long enough to make it into the black hole, you would see lights
being sucked in towards the center of the hole, and then you would enter a place where no one is for
sure what would be seen. Scientists have a term for the very center of a black hole called the
Singularity, a place where there is infinite gravity, something not easy for anyone to comprehend. Since
it’s so hard to comprehend, some scientists define the singularity as a word meaning ‘I don’t know’ or
‘I’m clueless.’ It is also thought that since black holes break so many laws of physics that there are
bigger laws being used by black holes that we just don’t understand yet.
Is there any proof outside of scientific theory to suggest that black holes exist? While you can’t see a
black hole directly, since nothing including light can get past the holes horizon, sometimes seeing
nothing is just as good as seeing something. In January of 2001 astronomers found evidence of a black
hole by essentially ‘seeing’ nothing. Using the Chandra X-ray Observatory NASA observed several
systems containing a Sun-like star that is orbiting either a black hole or neutron star. In doing so they
found evidence of an event horizon. Since black holes are the only thing that can have an event horizon
scientist had plenty of reason to believe they had proof of the existence of black holes.
“By detecting very little energy from these black hole candidates, we have new proof that event
horizons exist,” said Michael Garcia of the Harvard Smithsonian Center for Astrophysics,
Cambridge, MA. “It’s a bit odd to say we’ve discovered something by seeing almost nothing, but,
in essence, this is what we have done.” (NASA website)
While observing a massive, compact object named Cygnus X-1, using the Hubble Space Telescope, NASA
found ultraviolet light fading and then disappearing as it swirled closer to the object. If there were no
event horizon the light would have crashed to the surface of the object, and in doing so created a bright
flash. So, again NASA had found a bit of proof of an event horizon by seeing nothing. In this case it was
the lack of being able to see the ultraviolet lights crashing on the surface of Cygnus X-1 that gave
evidence to the existence of an event horizon, and therefore black holes.
In January of 1995 it was reported that a nearby galaxy containing a powerful source of microwave
radiation, was found to have a very large mass all confined to a very small volume. This discovery was
made by mapping the velocity to within half a light year of the galaxies center, and therefore concluding
that the object was less than half a light year in radius. The combination of findings that the mass was
so enormous and that the volume was so small in comparison, led researchers to believe they’d found
proof of a black hole.
About the same time a second and more compelling discovery was made. Using an X-ray telescope,
astronomers were able to measure the stars near the nucleus of one galaxy to be moving at incredible
speeds. Radiation from these stars was also observed to be redshifted in the same way scientists had
predicted radiation would be when coming from the event horizon of a black hole. While the possibility
is there that this could be caused by some other phenomenon, it’s easiest to believe that this is caused
by a black hole.
In recent years, there has been a lot more conclusive evidence to suggest that black holes are at the
center of every galaxy. In 2004 the Swift Probe was launched to search for black holes being born. This
is done through searching the Universe for gamma ray bursts, which have been discovered to be an
effect from a black hole. The swift probe, even though it can only see a fraction of what is out there, has
been very successful. It detects at least one gamma ray burst a day!
In December of 2008, a team of scientists reported their findings of a 16 year study on what they
thought to be a super massive black hole at the center of our very own galaxy. They had to rely on a
collection of 28 stars orbiting where they believed the black hole to be, since no light will escape past
the event horizon of the black hole, and therefore we cannot see the black hole directly. However, by
tracking these stars scientists were able to conclude that the object the stars were orbiting had a
concentration of mass over four million times that of our own Sun.
“The stellar orbits in the galactic center show that the central mass concentration of four million
solar masses must be a black hole, beyond any reasonable doubt.” (Study leader Professor
Reinhard Genzel.)
Again, the fact that scientists could not ‘see’ the object at the center was a key observation to lead the
team to believe they may have found a black hole. After finding evidence as to the mass of the object at
the center the team felt they had overwhelming evidence to conclude that this was in fact a supermassive black hole. It was also found in our own galactic neighborhood, the Milky Way, which gives
scientists reason to believe that there are far more out there that we just haven’t discovered, or lack the
technology to do so at this time.
To this day astronomers continue to study the black hole at the center of our galaxy. In Hawaii at the
Keck observatory scientists keep a close eye on our very own black hole. They continue to see stars
moving at millions of miles an hour around where the black hole is believed to be. A super massive
black hole is the only thing known to have the power to cause these stars to swing around the center of
our galaxy as fast as they do. While the black hole at the center of our galaxy is said to have the same
mass as 4 million of our Suns, we’ve discovered larger black holes.
Our closest neighboring galaxy, Andromeda, also has a black hole at its center. This black hole is
significantly larger than the one found in our own Milky Way; it is 140 million times as large as our Sun.
This is even miniscule to the black hole found at the center of the M87 galaxy, which is believed to have
a mass equivalent to 20 billion times our Sun.
Another effect of black holes has led to discovering the location of other black holes, Quasars. While,
gamma ray bursts happen in the stars final milliseconds of life, quasars happen when the black hole has
gotten so large and become so powerful pulling in more and more that it can take no more. The
Chandra telescope can find quasars and has found over 200,000. Each quasar observed is a sign post to
another young galaxy, with a black hole at its center.
Now astronomers are linking together telescopes to create a virtual telescope. Essentially they are
creating one giant telescope almost as large as the Earth itself. The hope of this project is to get a
photograph of the event horizon itself. The project has been successful to date, with telescopes all over
linking together. They hope that as more and more satellites link up, the network will be able to prove a
more clear and accurate photograph of an event horizon.
In September of 2010 an observation was claimed to have seen another phenomenon that happens
around the event horizon of a black hole, Hawking radiation. Hawking radiation got its name from the
scientists who first discovered it, Steven Hawking. Hawking was one of the most involved scientists in
the studies of black holes, and has written books for the scientific community, as well as the general
public, describing black holes. Hawking had studied and learned enough about black holes to realize
that rotating black holes did actually emit radiation. This radiation is not directly from the black hole
itself but instead from virtual particles moving at great speeds around the event horizon because of the
black holes immense gravity. This tidal gravity causes the two virtual particles, a particle-antiparticle
pair, to be torn apart with great force. This causes the particles to become two real particles. One is
drawn in to the black hole, and the other is expelled outwards and is the radiation that surrounds black
holes. Hawking had found black holes emit black body radiation through quantum effects.
The particle that fell into the black hole must have a negative energy, in order to preserve total energy.
Because of this, the black hole loses mass; this is known as black hole evaporation. This finding shows
that black holes that lose more mass, through black hole evaporation, than they take in are believed to
dissipate and eventually shrink until they vanish, or worse. Hawking believes that they would continue
emitting radiation after they stop spinning and eventually explode. However, this process, from the time
a black hole having the same mass as two Suns is created to the time it should explode, would take
almost 1067 years. The Universe is believed to be only about 12 to 15 billion years old, so we may have
to wait until any of this can be proved; however, smaller micro black holes are believed to emit more
radiation and therefore shrink and dissipate faster. Scientists are currently trying to create a micro black
hole to further study them.