Deep within the universe lurk massive objects which seem to defy the laws of physics. They twist space and time into an endless void that no signal can attempt to escape. These objects are known as black holes, and are objects that are constantly undergoing scientific study. Their existence was first predicted by Einstein's Theory of General Relativity, and scientists have searched for them ever since. Why are we interested in black holes? The answer to this question is simple; they may very well be the key to unlocking the mystery of how our universe was formed. However, before we can use them as a means of answering one of sciences most daunting questions, we must first understand black holes themselves.
The first step toward the understanding black holes is to gain an understanding of how science happened upon them in the first place. In 1916, Albert Einstein published a theory which he claimed united the ideas presented in special relativity, and classical Newtonian gravitation. This was an important discovery, because until Einstein's solution these two principles of physics had been at odds with each other. Einstein called his unifying theory “General Relativity.” According to this theory, as an object becomes sufficiently massive and compact it will form a region of space from which no signal can transmit, not even light itself. This means that black holes are points of mass that have the capability to warp space and time in such a way that their gravitational pull forms an event horizon at which no signal from the inside of the hole can reach any point outside the hole. Understandably, scientists wanted to further investigate if the formation of such objects was even possible, and if so, what the implications of their discovery might be.
Before the search for black holes could begin, scientists needed to take a closer look at what general relativity has to say about them. The first thing that relativity has to say relates to the different types of black holes. “According to theory, there might be three types of black holes: stellar, super-massive, and miniature black holes - depending on their size,” . These different black holes hold properties that affect science independently. Stellar black holes are possibly the most observable, being formed as the final step in stellar evolution. It is this type of black hole that has lead to much in the way of understanding these daunting cosmological beasts. Black holes of the super-massive variety taunt scientists with their possibilities, but extremely limited methods of observation. It has been speculated that these black holes may have been responsible for as much as half the radiation emitted during the Big Bang. “Astronomers are finding out that these objects may have been critical to the formation of structure in the early universe, spawning bursts of star formation, planets, and even life itself,” . However, since these scientific marvels lurk at the center of galaxies, and are not inherently visible, scientists must settle for speculation. The final type of black hole as predicted by general relativity is the miniature black hole. These holes are thought to have formed shortly after the Big Bang, and can, in theory, “evaporate.” This means that these rather small black holes have the potential to degrade to a point at which they would explode with a force trillions of times more powerful than any man made explosion. These black holes, however, have never been observed, nor is there any clear evidence that they even exist at all.
Scientists then began to search for any physical signs that black holes might actually exist. In 1963, an astronomer by the name of Cyril Hazard designed a test to isolate a region of intense radioactivity. During the test he was successfully able to locate a star like object near the constellation Virgo as the source of one such region of radioactivity. This source, as well as many others like it, has been dubbed “quasi-stellar radio sources,” or quasars for short. These quasars baffled scientists since they emitted so much radiation for their rather small size (nearly 100,000 times smaller than the radius of out galaxy). It became clear that no star could emit such amounts of radiation. The answer to the quasar question happens to confirm the existence of black holes. “It turns out that super-massive black holes are luminous precisely because the material falling into them is squeezed and cajoled into producing radiation before disappearing forever below the horizon,”. In essence these quasars are the detectable footprint of super-massive black holes. Other smaller stellar black holes have been identified by their “shadow,” which is really the visible event horizon, that they cast on nearby stellar objects.
