Black Holes: Enigma of the Known Universe

The millions upon millions of stars in our known universe are constantly burning hydrogen, creating an intense amount of energy that can be felt within the near reaches of the star's gravity. This process, called fission, started 6 billion years ago when our universe came into existence and has continued to this day. But a question can be asked: how long can these stars burn with such intensity? We know now that these stars are capable of surviving billions of years on the energy supply that they have. Knowing this, another question arises: what happens to the star when it runs out of energy? Does it just shut off like a light bulb into the night sky? These questions were the leading factors in the discovery of the phenomenon known as a black hole. Black holes are defined as regions of space so tightly packed with matter that nothing, not even light, can escape.

The research that went into perceiving black holes was sometimes controversial, especially among astronomers and physicists. Sir Isaac Newton took the first step take towards understanding black holes, however indirect it may have been. His book, Principia, written in 1687, outlined the basics of Newtonian physics, including the laws of motion, gravity, and other areas of physics. Also included in the text was the idea that time and space are absolute, meaning that the same laws applied to time and space wherever one went in the universe. This idea, however, was discredited years later and a new idea came about.

In 1905, physicist Albert Einstein, before his renowned career, looked over the ideas of Sir Isaac Newton and theorized that Newton was wrong in that space and time were not absolute but were indeed relative. This was the start of a new thought process in regards to time and space, which are referred to as spacetime because the two words are not separate entities. Einstein soon came up with more concrete thoughts on his theory, which we refer to now as relativity.

First, Einstein maintained that everyone has a different experience of time and space. This is confirmed through experimentation. One idea that is related to spacetime and how it is experienced is that the faster an object travels, the smaller the dimensions the object appears to have. Therefore, a car traveling 55 miles per hour appears smaller than a car traveling at ten miles per hour. A second, and even stranger, idea related to the experience of spacetime is this: clocks at rest move quicker than clocks that are not moving rapidly. In other words, a clock in motion is moving slower than one not in motion. This concept proved that space and time are not separate ideas, since motion and time are so closely linked.

In 1915, Einstein completed his theory of relativity. The theory basically stated that though gravity may hold all matter in the universe together, there is some force that keeps this matter from collapsing in on itself, a type of "anti-matter." He also surmised that spacetime was curved, a much more complicated side note to a simple physical idea. Spacetime curvature was the cause of many occurrences in the universe, including tidal waves on Earth. Albert Einstein's ideas would go relatively unscathed for some thirty years, until three scientists came up with an important discovery.

In 1957, Wheeler, Harrison, and Wakano came to a common consensus: the common fate of enormously large stars, referred to as massive stars, was one of implosion. But that is where the agreement ended. Some physicists believed that the then theoretical idea of black holes was too far fetched to be the explanation for a star's final resting spot. Others believed the idea to be true. The argument continued until 1972, the year that the first possible black hole candidates were discovered. Using a combination of X-Ray and radio wave measurements, as well as optical telescope observation, convincing evidence was provided that may have proven Cygnus X-1 as a black hole orbiting a still-functioning star. A debate still continues as to whether Cygnus X-1 is a black hole or not, but is the most prominent candidate to date due to the amount of manpower and time put into the observation.

Presently, research is still being done to uncover the exact features and characteristics of the black hole. Since no electro-magnetic radiation comes from the black hole, observers on Earth cannot see it. The only way astronomers have been able to determine the structure of a black hole is through the use of equations of general relativity. There are a few things that astronomers have surmised. One is an area called the event horizon, which is the boundary between the endless darkness of the black hole and the rest of the universe. Second, we can detect black holes by observing gravitational waves, which are caused by massive stellar bodies losing their magnetic field when collapsing into a black hole. Third, astronomers have been able to put classifications to black holes.

One classification for black holes deals with rotation. One type of black hole, called a Schwarzschild black hole, does not rotate. Since the matter that formed the black hole was not rotating, the black hole that is formed does not rotate. In a Schwarzschild black hole, the matter that is sucked in usually falls to a center point, called a singularity. The second type of black hole, which does rotate, is called a Kerr black hole. The matter that forms the black hole in these cases does have momentum, causing the black hole to rotate, sometimes faster than the pulsars that we observe from Earth. A few differences exist between this type of black hole and the Schwarzschild black hole. One is that the Kerr black hole has a region just outside of the event horizon called the ergoregion. In this space, nothing can remain at rest without being sucked into the deep abyss of the black hole. However, if something moves fast enough, it can pass through this region safely without being caught in the gravitational pull of the black hole. Another difference is that the theoretical shape is significantly different. The Kerr black hole is not so much spherical as the Schwarzschild blck hole as it is more doughnut shaped, with the ergoregion surrounding the event horizon.

A second classification deals with size. The biggest of all black holes that we know of to the present date are the heavyweights. The mass of such an enormous stellar object is equal to that of one billion suns with the area the size of our solar system. These black holes tend to be formed from some of the older galaxies since most of their energy has been expended. The second classification is a middleweight black hole. The mass, in comparison to the heavyweights, is a significantly smaller 100 to 100,000 suns which take up an area the size of our Moon. The way these black holes are differentiated is by the effect they have on surrounding stellar bodies, more usually on stars. If there is a redshift (a movement away from Earth) that means that there is a blueshift toward something else. The speed in which these objects move determines the power of the attracting force.

In the past decade, a few things have occurred that have helped further research in the area of black holes. A positive byproduct of new technology came in the form of new ways of measuring black holes. The traditional method of measuring black holes was to observe the effect of gravitation by black holes on nearby stars. The problem with this was that uncertainty arose when dealing with distant stars. The new method deals with the observation of the amount of gas entering a black hole. By measuring the mass that enters the black hole, the mass that the black hole contains can be determined. The only problem with this type of measurement is that it only deals with rotating, or Kerr, black holes since the gas is rotating in the ergoregion. This discovery may lead to new ways of observing all black holes, but for now is more of a complement than a replacement since it only deals with a specific type of black hole.

A theory that arose recently is that black holes emit energy levels equal to that of a star. Up until a few years ago, observations showed only trace amounts of energy coming from black holes, with most of this energy being clouded by dust and gases. But with the implementation of new technologies, energy levels emitted by black holes have shown to be much, much higher than previously thought. The swirling gases that approach the event horizon en route to the black hole cause the emission of this energy. These gases gain tremendous speed and therefore gain significant amounts of energy before plunging into the darkness of the black hole. Not only was it found that more energy was being emitted but also different types of energy. Previously, the only energy observed from Earth was in the area of visible light. With the new ways of observing, it was found that gamma rays, radio waves, and X-rays were being emitted as well.

The black hole is an area of physics and astronomy that is still controversial but has been cleared some by new research and the constant debating. These enigmatic stellar objects may never be fully understood because they are only truly explained by theories and mathematical equations. Since the average person on Earth cannot observe these black holes, they may not care to understand more about them. But through understanding more about the black hole and the science that explains it, we understand more about the history of our universe, as well as the fate of most stars. It may never directly effect us, but it is still the embodiment of all that astronomy is all about: the mysterious and unexplainable that we try to explain.