Paste your essay in here… A black hole is a theoretical massive object, whose gravitational field is so intense that no electromagnetic radiation can escape. They are a relatively recent discovery. However, theories of their existence have been put forth as far back as the mid-18th Century. Once there was confirmation of their existence, further study of black holes and their properties led to explanations for phenomena in the universe that had yet to be understood by scientists. Black holes have assisted the research of physicists ever since their discovery.
The idea of a black hole was first proposed in 1783, by a philosopher and clergyman named John Michell (Michell 1776). His theory was based on the accepting of Newton’s corpuscular theory of light, which stated that every source of light gives off a large number of particles called corpuscles. These corpuscles were said to be perfectly “elastic, rigid, and weightless” (Newton 1730). Naming them “Dark Stars” (Cosmos: A Spacetime Odyssey), Michell proposed that “all light emitted from such a body would be made to return towards it, by its own proper gravity” (Michell 42). Michell goes onto suggest how one might identify a “Dark Star,” admitting that it would be impossible to identify on its own due to the absence of light. He suggested that instead they look at the surrounding stars, writing “we could have no information from light; yet, if any other luminous bodies should happen to revolve around them, we might still perhaps from the motions of these revolving infer the existence of central ones with some degree of probability” (Michell 50). Michell’s proposition was cause for excitement at first, but the corpuscle theory of light was later disproven. The idea of light being a particle was replaced with it being a wave, leading scientists to question whether or not gravity would have any effect on it (Montgomery, Orchiston, & Whittingham 2009). In the early 20th Century, two physicists would once again dabble with these mysterious phenomena.
Albert Einstein, a prominent theoretical-physicist, and Karl Schwarzschild, an astrophysicist. moved the concept of black holes from theory to more concrete mathematics. In 1915, Einstein published theory of general relativity. This theory revealed much about the nature of gravity, stating that “massive objects cause a distortion in space-time,” the result being the force of gravity (Redd 2017). Einstein’s work produced the “Einstein Field Equations”, which were used to describe the interaction of gravitation as a result of the distortion in space-time (Einstein 1916). It was Karl Schwarzschild who first took these equations and found a solution that characterized what was still the theoretical black hole. The black hole Schwarzschild characterized was a “simple static black hole” with no charge. They were often called Schwarzschild black holes after the man who had discovered them (Schwarzschild 1916). Einstein’s equations were used to predict four other types of black holes, which were classified by mass. From largest to smallest, there is the supermassive black hole, the intermediate-mass black hole, the stellar black hole and the micro black hole. Through Einstein and Schwarzschild’s work, the theory of black holes was further developed. However, there had not yet been a confirmation of the suggested gravitational body’s existence.
The first promising evidence of a black hole was discovered in 1950s. Until this point, scientists were skeptical of the possibility of a such a “monstrous thing” in nature, but with the discovery the phenomena they called quasars, their opinion on the subject began to shift. Quasars are objects that are so bright, they were initially mistaken for nearby stars, when in reality, they were billions of light years away. They released an enormous amount of energy and light, so much that nuclear fusion (the process by which energy is generated in stars) would not have been enough of a force to create it. After much theorizing, some suggested that quasars were evidence for black holes existing. In the 1970s, Fred Lo, who would become director of the National Radio Astronomy Observatory, discovered new evidence of black holes existing. He used a radio interferometer to observe the middle of the Milky Way, which is essentially using multiple telescopes to increase the observational power and resolution. What Lo found was a hint of a “compact radio wave source—what astronomers believed would indicate a black hole.” After this, in 1974, two astronomers performed the same experiment using two radio telescopes to observe the center of the Milky Way themselves. What they found was a confirmation of Lo’s discovery, encountering an intense source of radio waves. The decided to name the object “Sagittarius A*.” While this was an important discovery, they had no way of measuring its size or mass, which were necessary in determining an object to be a black hole or not. Astronomers continued to observe the massive body with infrared telescopes and found that there were several stars orbiting the “Sagittarius A*” itself. They hoped to observe the orbits of the stars around the black hole and use the laws of orbital motion developed by Kepler to determine its mass. At first, they encountered a problem with the observations, as infrared was sensitive to “atmospheric fluctuations” from the Earth, which would cause stars to blur together. This was later solved by an astronomer named Andrea Ghez. She took very short exposures, which “freeze the interference effects of the Earth’s atmosphere” (Matthew 2017).