# Term Paper: Black Holes Astronomy Encompasses Vast Topics

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Black Holes

Astronomy encompasses vast topics and includes many subjects. Among these subjects is the area of study involving black holes. Although there has been a great deal of research concerning this subject, there are still many factors concerning black holes that are still unknown. The purpose of this disccusion is to explain the phenomenon of black holes and how the theory of the black hole evolved. Let us begin this discussion by providing a definition for black holes.

What are black holes?

Hawkins (1998) explains that Black holes are theoretical articles that symbolize the eventual state of collapsed matter. The author explains that In principle they may be of any mass, but there are certain mass ranges where we believe conditions can easily arise for them to form. For example, dead stars with more than four times the mass of the Sun no longer have the energy to resist the power of their own gravity to crush them almost out of existence, into the secluded annihilation of a singularity. This is the infinitely dense and infinitely small state of being where atoms are decimated into their primordial parts and cannot interact with any form of radiation (Hawkins, 1998)."

The theory also asserts that not even light can escape the gravitational pull created by black holes. Black holes can also be thought of as compact bodies that are not atomic. In any case the mass of a black hole is one aspect of the totality of what was created as a result of atomic material that was a part of the early universe. However the idea that this material reverted back to a state that is nonatomic is not relevant as it relates to discovering dark matter (Hawkins, 1998).

In any case, the theory of black holes is usually expressed as it relates to Einstein's theory of general relativity (Hawkins, 1998). This theory asserts that gravity is almost identical to the shape of space. In addition this theory purports that gravity is not only an attractive force but also relates to the slopes and curves of space. In other words, gravity is responsible for the manner in which massive bodies are able to distort space (Hawkins, 1998). For example, a heavy object such as a ball would stretch and curve the surface of a rubber sheet and as a result cause less weighty balls to move toward the heavier ball (Hawkins, 1998). A black hole is similar to this in that it is the place where "space is so curved in upon itself that even light and other carriers of information cannot escape, but keep going round and round within the black hole's "event horizon" thinking that they are traveling in a straight line. Like a bottomless whirlpool, a black hole can draw in material and information from the rest of the Universe, but it gives back nothing (Hawkins, 1998)."

This means that the entire Universe is finite and similar to a black hole because it is restricted by its own event horizon, within which light can travel in a straight line. This is true whether or not the light curves back upon itself (Hawkins, 1998). A straight line is defined as the course that light travels. In this kind of universe, straight lines that are parallel will meet in the way that lines of longitude meet at the poles (Hawkins, 1998). From this detached perspective the overall form of the Universe is analogous to the surface of a sphere. As such, the value of ? would be more than 1.

With these things being understood, the universe would inevitably collapse under its own weight into a spectacle because eventually it would no longer possess the energy to resist the strength of its own gravity (Hawkins, 1998). The author points out that a closed universe has often been presented as a snake swallowing its own tail. The geometry of such a universe is also identical to that of the surface of a sphere, as the sum of the angles of a triangle is more than 180 degrees (Hawkins, 1998). In addition within an open universe, the typical density is not more than the critical density. In fact it is believed to be saddle shaped and as such the sum of the angles of a triangle will be less than 180 degrees (Hawkins, 1998). At this point parallel straight lines associated with the path light travels will become progressively more remote as it relates to their capacity to communicate with each other in perpetuity (Hawkins, 1998).

As it relates to how large a black hole is, Bunn (1995) asserts there is not a restriction in principle as it relates to how massive a black hole can be. Therefore, any amount of mass can develop into a black hole if it is packed together at a high enough density. Many researchers believe that the majority of black holes were produced be the collapse of the massive stars, and as a result those black holes may weigh the same amount as a massive star. The author points out that "A typical mass for such a stellar black hole would be about 10 times the mass of the Sun, or about 10^{31} kilograms. (Here I'm using scientific notation: 10^{31} means a 1 with 31 zeroes after it, or 10,000,000,000,000,000,000,000,000,000,000.) Astronomers also suspect that many galaxies harbor extremely massive black holes at their centers. These are thought to weigh about a million times as much as the Sun, or 10^{36} kilograms (Bunn 1995)."

According to the research the idea or concept of the black hole is a rather simple one. The black hole is simply occurs when matter collapses and not longer has the energy to fight against the gravitational pull. In addition the pull created by the black hole is so strong that not even light can escape it. Now that we have garnered a greater understanding of the definition of a black hole let us concentrate upon the history of this theory.

History of Black holes

According to Hawley and Holcomb (1998) from a historical standpoint the black hole is viewed as an extreme outcome of the Einstein's theory concerning general relativity. However, the theory of the black hole can even be explained if one considers Newton's theory of gravity. This gravitational theory asserts that any planet or star has at its surface gravitational acceleration (Hawley and Holcomb 1998). In order to escape from the planet or the star must have a velocity that is significant enough to rise above the gravitational pull. This type of velocity does indeed exist and it is referred to as escape velocity (Hawley and Holcomb 1998).

On the planet earth, escape velocity is 11 kilometers per second. If this escape velocity was the same as the speed of light and there was a star with that significant an escape velocity light, would not be able to depart from the surface of that star; the star would be dark (Hawley and Holcomb 1998). In addition any light that exist on the surface of this star could ascend, but similar to a ball tossed into the air, the light would ultimately turn around and fall back down (Hawley and Holcomb 1998). When this theory was first asserted astronomers did not yet know that the speed of light in vacuo is the final speed limit, but with that additional knowledge, it can be surmised that nothing could escape from this type of star (Hawley and Holcomb 1998).

Hawley and Holcomb (1998) also explain that the theory of the general relativistic black hole formed after the manifestation of the finished version of Einstein's general theory of relativity in the year 1916 (Hawley and Holcomb 1998). The authors further explain that Despite the great complexity of the Einstein equations, the German astronomer Karl Schwarzschild found one of the first solutions, almost immediately after Einstein published his results. Schwarzschild assumed a perfectly spherical, stationary ball of mass M, surrounded by a vacuum, that is, empty space. This is not a bad approximation to a star; the Sun, at least, rotates slowly and is very close to spherical, and, as far as we know, the Sun is a typical star. Schwarzschild then solved Einstein's equations to compute the spacetime curvature in the exterior of the star. Such a solution consists of a specification of the geometry of spacetime; this description can be encapsulated in the metric coefficients (Hawley and Holcomb 1998)."

The conjecture of Schwarzschild simplified the mathematics required to explain the theory of the black hole. First, he solved for the gravity in a vacuum outside the mass. This allowed him to set the stress-energy term T?

in Einstein's equation equivalent to zero and focus only on the geometry term (Hawley and Holcomb 1998). Because Schwarzschild was investigating the space surrounding a spherical mass, he used spherical spatial coordinates, composed of a distance R. from the midpoint of the mass, in addition to the inclination from the starting point expressed in terms of…
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