This means that the star should only depend on the distance from the star (Hawley and Holcomb 1998). As a result of this fact, it was not possible to disregard the angular terms (Hawley and Holcomb 1998). Lastly, the star along with its gravitational field do not change with time, this means that the metric terms are independent of time, but only when the time coordinate is chosen correctly (Hawley and Holcomb 1998). The time coordinate Schwarzschild used was a rational one because it can be correlated to the time calculated by an observer who was a significant distance away from the central mass, where gravity's effects ebb down to zero (Hawley and Holcomb 1998). The authors point out that Schwarzschild radius is the identical to the radius used for the Newtonian dark star (Hawley and Holcomb 1998). However because Newtonian gravitation is suitable as it relates to a good approximation, it should be anticipated that the radius would not be too far from its prediction (Hawley and Holcomb 1998). However the black hole is a much more interesting and foreign theory than is the dark star, and as such reflecting upon the black hole as if it were a Newtonian dark star may cause a misunderstanding of the important aspects of the black hole (Hawley and Holcomb 1998).

With these things being understood, why is every round object not considered a black hole? The answer to this has to do with the fact that the Schwarzschild radius can be found in the outer surface of any "normal" object, including a neutron star. For instance, the Schwarzschild radius of the Sun is 3 kilometers; on the other hand the solar radius is more than 1 million kilometers. In addition the Schwarzschild radius of the Earth is below 1 centimeter. Again, the solution presented by Schwarzschild relates only to the empty space contained in the exterior of the sphere (Hawley and Holcomb 1998). This means that if the Schwarzschild radius is less than the radius of the body, it is immaterial inside the body (Hawley and Holcomb 1998). The author also asserts that the metric contained inside of a star is not consistent with a Schwarzschild metric, but is instead a different metric that incorporates the existence of the matter which produces the gravitational field (Hawley and Holcomb 1998). A black hole can only be formed if the object has totally collapsed and vanished beneath its Schwarzschild radius (Hawley and Holcomb 1998).

The authors further explain that at the Schwarzschild radius, the coefficient of the time interval in the Schwarzschild metric is zero (Hawley and Holcomb 1998). As a result, the time interval itself becomes infinite (Hawley and Holcomb 1998). Likewise, radial intervals decrease to zero, which is the definitive length contraction. These effects occur as a result of the choice of coordinates, and these coordinates are not ever absolute even as it relates to Newtonian physics. Nonetheless, the length contraction, time dilation, and other relativistic effects that are dependent upon the metric coefficients, are actual physical occurrences and can be calculated with the right type of instruments (Hawley and Holcomb 1998). In addition the gravitational field in the vicinity of the black hole is more significant at small radius than it is when it is at some distance away, and as a result light moving from near the object endures a gravitational redshift (Hawley and Holcomb 1998).

As it relates to the black hole, any light sent from the Schwarzschild radius is perpetually redshifted (Hawley and Holcomb 1998). As a result the sphere that is derivative of the Schwarzschild radius is reflective of a surface from which light is not able travel to an outside observer. In addition an observer from outside this horizon can not see within the horizon because the inside of the black hole is infinitely unable to communicate with the rest of the universe (Hawley and Holcomb 1998). Likewise the Events that take place inside the black hole can have no contributory contact with events outside the black hole (Hawley and Holcomb 1998). This limit that exists between the inside...

The event horizon can be described as the point of no return, at this point no can ever escape the black hole. The Schwarzschild radius is responsible for identifying the event horizon of the black hole (Hawley and Holcomb 1998). The authors further insist,
From outside a black hole, the event horizon seems to be a special location. What would happen if an advanced civilization were to launch a probe toward a black hole? To the observers watching from a safe, far distance, the infalling probe's clock slows down; radio signals from the probe come at increasingly longer wavelengths due to the gravitational redshift. The probe approaches closer and closer to the horizon, but the distant observers never see it cross over into the hole. Time seems to come to a halt for the probe, and the redshift of its radio beacon goes to infinity, as measured by the faraway astronomers. At some point the last, highly redshifted signal from the probe is heard, and then nothing more. The probe disappears forever (Hawley and Holcomb 1998)."

Overall the research seems to indicate that the theories and concepts developed by Schwarzschild are significant in explaining how the theory of black holes came into existence. The research also seems to indicate that theories developed by Albert Einstein and Isaac Newton are also consistent in defining and confirming the accuracy of the theory of black holes.

Are black holes just a theory?

According to Bunn (1995) there is evidence that black holes exist even though they cannot be seen with the naked eye. The author asserts that scientist have begun to rely on indirect evidence to support the claim that these phenomena are real. The author explains that if there is a region of space that is believed to contain a black hole scientists can measure how much mass exist in that region. If there is a significant or large mass condensed in a small volume, and if that mass is dark in appearance it is probably a black hole in that region (Bunn 1995). The author also contends that there are two types of systems that have been found to contain black holes: the centers of galaxies (and X-ray-emitting binary systems (Bunn 1995).

The author further asserts that there are eight galaxies that are thought to contain black holes. The masses found at the cores of these galaxies are one million to a billion times the mass of the Sun (Bunn 1995). This mass can be calculated by observing the speed with which stars orbit around the center of the galaxy (Bunn 1995). When these orbit speeds are fast the gravitational force required must be stronger so that the stars can be held in their orbits (Bunn 1995).

There are two reasons why scientists believe that these objects are black holes. The first reason involves the fact that they are too dense and dark to be clusters of stars or singular stars (Bunn 1995). The second reason suggests that the only probable theory to explain these objects confirms that such galaxies contain very large black holes at their cores (Bunn 1995).

The author asserts "If this theory is correct, then a large fraction of galaxies -- all the ones that are now or used to be active galaxies -- must have supermassive black holes at the center. Taken together, these arguments strongly suggest that the cores of these galaxies contain black holes, but they do not constitute absolute proof (Bunn 1995)."

Conclusion

The purpose of this disccusion was to explain the phenomenon of black holes and how the theory of the black hole evolved. We found that the theory arose as a result of Einstein's theory of relativity, Newton's theory of gravity and the dark star and Schwarzschild's radius. The research also found that there is significant evidence that suggest that black holes truly exist.