By Sarah R.

There are currently many scientific events phenomenons in  cosmotology that can only be explained by theories and specific physical evidence. One of those mind-bending phenomenons are black holes. Black holes are based off General Relativity. A Black hole is an area in space that has a gravitational pull so powerful that nothing (including light) can escape it's event horizon (or surface). When studying the topic of Black holes, it is important to keep an open mind and have some previous history of related topics.

History and Formation of Black Holes

One of the first people to introduce the idea that an object had a gravitational pull strong enough to swallow light was a British Astronomer named John Michell in 1795. Later, a mathematician named Pierre-Simon Laplace came to the same conclusion in 1795. In the Nineteenth century, black holes were widely ignored for light (at the time) was thought to be massless, therefore not effected by gravity. Also, the first black hole theories were "Newtonian Black Holes," black holes that could prevent light from escaping but not physical objects (like a rocket ship). Later, in the 1900's, Einstein developed his theory of General Relativity, from which Black Holes are now described with. The theory states that a large amount of mass present in a very small region of space warps the paths of space inward towards the center of volume, preventing any kind of escape. Karl Schwarzschild later described the gravitational field outside a spherical, non-moving mass,  proving that a black hole could theoretically exist (for more on Schwarzschild, see Planck Time 2009). In the mid 1960's the term "black hole" was coined as the name for these regions of space. We now also use quantum mechanics when thinking of black holes. Research shows that it is possible that black holes do not hold onto matter forever, for they leak thermal energy known as Hawking Radiation, therefore making it so they have a finite lifetime. 

Black holes are generally formed by the gravitational collapse of stars. Stars collapse usually when they don't have enough fuel left to run. The star's temperature becomes too low to stop it from collapsing under it's own weight. The stars have to be large in mass and heavy for them to be powerful enough to form black holes. The stars collapse on themselves, crushing the center to a point of 0 volume, or singularity. A star would have to at least be a mass 10 time's greater than the sun's to form a black hole.

Different Parts of a Black Hole and Proof of Existence

There are many different types of Black holes with many different names for their qualities. In this article, we will mainly be focusing on Schwarzcshild Black holes, ones that do not rotate and have no charge or angular momentum. The first important part is the surface or edge of the Black hole, known as the Event Horizon. At the center of the black hole is singularity. Singularity is an infinite spacetime curvature. As an example, if you were to fall into a black hole, at the end of your fall you would reach a point where the hole's mass becomes compressed into one area with 0 volume, making the density infinite. A part of a rotating black hole is an Ergosphere. An Ergosphere is a region of spacetime around a black hole where it is impossible to stand still. Black holes are thought to be mostly full of space and invisible to the eye due to the black space surrounding it. So how do we know of a black holes existence? We theorized black holes from behaviors of stars and their gasses surrounding the holes. Stars were found orbiting around an unseen object, which we now theorize to be the event horizon of the black hole. Also, gasses from the stars can be seen spiraling inward. This causes them to heat up and give off large amounts of radiation that are picked up by earth telescopes. 

 

Effects of Falling Into a Black Hole

Before explaining what effects one would feel while falling into a black hole, it is important to know why nothing cannot escape a black hole. An object needs to be completely free of a black hole's gravitational field to escape. Because of the black hole's mass and density, an object needs to equal or exceed the speed of light. Because no object can exceed the speed of light, scientists infer that nothing can escape the black hole. It is also important to know one of Albert Einstein's concepts, the concept of spacetime. This is the concept that that space and time are not two different concepts, but are interrelated, or connected. In spacetime, and object is not free to move wherever; it must always move forward in time and cannot change it's place in space that is faster than the speed of light. Now that you understand a little background, we can move onto the theorized effects of falling into a black hole.

The first thing to happen to an object that is nearing the event horizon of a black hole is Spaghettification. An object falling towards something with a strong gravitational field feels a force stretching it towards the object that has the gravitational field. Closer parts of the object feel a stronger attraction, causing the object and it's atoms (even nucleons) to stretch out towards the black hole. Hence the name "Spaghettification" for one might say you get stretched out like a piece of spaghetti. This phenomenon can occur either before or at the event horizon, depending on the

size of the hole. 

Another feeling an object falling towards a black hole will feel is a slowing down of time relative to someone viewing from outside the hole. This is called gravitational time dilation. When the object approaches the event horizon, the gravitational time dilation will reach infinity, so the object would have the effect of feeling that time has stopped. From an outsiders point of view, it would look like the object falling into the hole were moving at an incredibly slow rate, growing dimmer and dimmer. In fact, the outside viewer never sees the object reach the event horizon, for the object eventually becomes too dim.

The next point is when the object reaches the event horizon. In fact, there is no major event that occurs when the event horizon is reached, and it is impossible for the object to tell when it has reached the event horizon. It takes a finite amount of time for the object to fall past the event horizon to singularity, measured by proper time (time according to the falling object). The object would still be able to view space outside the black hole.

The final destination would be reaching singularity inside the black hole. Forces act on it when the object approaches infinity. All parts of the object, including atoms and particles, are torn from each other right before reaching singularity. As for what happens when singularity is reached, no one quite knows for sure. 

Clearing Up Myths

Thanks to movies and TV, many wonder and believe certain facts about Black holes that are more fiction than reality. This includes the theory that a black hole is a wormhole. A wormhole is Basically an opening in spacetime that would enable someone to move great distances by passing through it. Imagine two black holed connected at their singularities with it being a passage instead of an end. This part of the wormhole would be called the throat. There is no scientific evidence that wormholes exist at all, and no scientific research or evidence that says wormhole's are present in Black hole's. It is still possible, though, for Black holes still remain a partial mystery.

Resources.

http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html

http://en.wikipedia.org/wiki/Black_hole#Formation_and_evolution

http://school.eb.com/all/eb/article-9015483?query=black%20holes&ct=null