Black Holes
The American scientist John Wheeler coined the phrase “black hole” in 1969 to describe a massively compact star with such a strong gravitational field that light cannot escape. When a star’s central reserve of hydrogen is depleted, the star begins to die. Gravity causes the center to contract to higher and higher temperatures, while the outer regions swell up, and the star becomes a red giant. The star then evolves into a white dwarf, where most of its matter is compressed into a sphere roughly the size of Earth. Some stars continue to evolve, and their centers contract to even higher densities and temperatures until their nuclear reserves are exhausted and only their gravitational energy remain. The core then rushes inward while the mantle explodes outward, creating neutron stars in the form of rapidly rotating pulsars. Imploding stars overwhelmed by gravity form black holes, where the core hits infinite density and becomes a singularity (some estimate it at 10^94 times the density of water).
John Michell and Pierre de Laplace, in 1783, showed that when the escape speed from the surface of a body equals the speed of light, Newtonian theory breaks down. According to general relativity, spacetime is curved and the curvature is a measure of the strength of gravity. Thus as a star contracts, its surface gravity increases and spacetime becomes more curved. At the Schwartzschild radius (Rs=2GM/c^2) spacetime is so curved that the body is enclosed, becoming a black hole wrapped in curved spacetime where not even light can escape it. Also, as a mass contracts, its surface gravity increases in strength and light rays emitted from the surface are increasingly redshifted and deflected (gravitational redshift=(l...
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...ðG^2*M^2/c^4. When two black holes encounter one another, they combine to form a single black whole whose surface area is greater than the sum of the horizon areas of the two initial black holes. A black hole can never split into two black holes, since this would decrease total surface area and thus entropy. Radiating away mass, does not violate the laws of thermodynamics, since, although the black hole’s surface area decreases, the emitted radiation carries entropy into space, thus neither creating or destroying entropy within the closed system of the universe.
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Hawking, Stephen W. A Brief History of Time. Toronto: Bantam Books, 1988.
Scientific American. Cosmology +1. San Francisco: W.H. Freeman and Co., 1977.
http://image.gsfc.nasa.gov/poetry/ask/abholes.html
Starting with black holes, Khalili describes the creation of one. I found that a black hole is what remains when a massive star dies. Because stars are so massive and made out of gas, there is an intense gravitational field that is always trying to collapse the star. As the star dies, the nuclear fusion reactions stop because the fuel for these reactions gets burned up. At the same time, the star's gravity pulls material inward and compresses the core. As the core compresses, it heats up and eventually creates a supernova explosion in which the material and radiation blasts out into space. What remains is the highly compressed and extremely massive core. The core's gravity is so strong that even light cannot escape. This object is now a black hole and literally cannot be seen because of the absence of light. Because the core's gravity is so strong, the core sinks through the fabric of space-time, creating a hole in space-time. The core becomes the central part of the black hole called the singularity. The opening of the hole is called the event horizon. Khalili describes that there are two different kinds of black holes:
The sixteenth president of the United States was none other than “Honest Abe” himself, or better known as Abraham Lincoln. Lincoln may have looked thin and weak physically, but he was actually pretty strong. He was also a fierce, sharp-witted lawyer and politician. He was never afraid of the challenges thrown at him. He held firmly to the things he believed to be right, even when the “majority” did not agree with him. Abraham Lincoln faced opposition as president because of his divergent moral views, ideas, decisions, and beliefs.
A black hole is a dead star in outer space. It is where planets and stars disappear at. The gravity of a black hole is way too strong ( Aguilar 39). The black hole is a weird object in outer space and a black hole is formed when two giant stars or more collapse together and basically vacuum anything that comes near it ( Aguilar 39). It might be gases around the black hole. People call it a black hole because light can’t escape from it (Cool Cosmos). So the hole appears black and the volume of the black hole is zero (Cool Cosmos).
The idea of Black Holes was first proposed in the 1700s by scientists John Michell and Pierre-Simon Laplace, who argued, independant of each other, that there might be objects in the universe with such a large gravitational force, that even light could be trapped. Published in 1916 Einstein’s theory of general relativity which included how gravity does affect light’s motion, gave way to scientific discoveries involving black holes. In Einstein’s own theory, he was only able to approximate the solutions to some of his own equations, however Karl Schwarzschild was able to provide the solutions. These solutions described objects like black holes that had such massive density that nothing could escape them. Schwarzschild theorized that if an object had such a small radius, that the escape velocity will be greater than the speed of light. Because as previously mentioned, nothing is faster than the speed of light, the object would be sucked into itself by it’s own gravitational pull, which would cause the object to disappear. What r...
Black holes are points in space where there are extreme gravitational pulls that prevent anything, including light, from escaping. The reason for such a strong gravitational pull is due to vast amounts of matter being contained in a small amount of space. Stellar black holes form from stars with a mass greater than 20 solar masses and can be a result of gravitational collapse. Gravitational collapse is a result of the star’s internal pressure not being able to resist the stars own gravity. When the star is exhausted of its nuclear fuel such that it cannot maintain a high enough temperature it will begin to collapse under its own weight (Seidel 2011). As the star collapses it causes a supernova which blasts the outer layers of the star into space while the core completely collapses under its own weight. If the remnant core left behind exceeds 3 solar masses there are no known forces that can prevent the core from completely collapsing into a black hole (p. 568 Bennett et al. 2013)
A Black hole is a theorized celestial body whose surface gravity is so strong that
Abraham Lincoln, an autodidactic early American, grew up amidst the unlikely setting of the American frontier to an impoverished and undistinguished family (Donald n.p.). Lincoln built himself up in a world built to bring him down, and rose “from [these] humble origins in Kentucky, to prominent positions in legal and political circles of Illinois, and then to the pinnacle of presidency” (Donald n.p.). Within two months of gaining presidency, in contempt of Lincoln’s noble efforts, the American Civil War broke out amongst the country, and Abraham Lincoln, undeterred by the considerable amount of stress he was under, managed to keep together and ultimately strengthen the broken nation (Gienapp). Lincoln boldly proceeded to denounce and even completely abolish slavery in America when he instituted the Emancipation Proclamation during the Civil War, and adeptly convinced the Senate to pass the Thirteenth Amendment (Hamilton). Abraham Lincoln, America’s sixteenth president, left a significant impact on the country when he left an admirable legacy for future Americans to appreciate despite his difficult upbringing and personal life, when he consolidated the Union despite a civil war, and when he led the revolutionary movement to abolish slavery despite the controversy.
Black holes were predicted by Einstein's theory of general relativity. According to Space.com “In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time. Einstein then spent ten years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.”
“Nearly all men can stand adversity, but if you want to test a man's character, give him power.” - Abraham Lincoln. Abraham lincoln proved himself to be a man of good character before and after he was given the power of presidency. Abraham Lincoln was one of the most pivotal presidents in the history of our country.
At the point of singularity the effects of Einstein's general theory of relativity become paramount. According to this theory, space becomes curved in the vicinity of matter; the greater the concentration of matter, the greater the curvature. When the star (or supernova remnant) shrinks below a certain size determined by its mass, the extreme curvature of space seals off contact with the outside world. The place beyond which no radiation can escape is called the event horizon, and its radius is called the Schwarzschild radius after the German astronomer Karl Schwarzschild, who in 1916 postulated the existence of collapsed celestial objects that emit no radiation. For a star with a mass equal to that of the sun, this limit is a radius of only 0.9 mi (1.5 km). Even light cannot escape the black hole but is turned back by the enormous pull of gravitation.
Abraham Lincoln served in many facets of the United States government and was also a respected lawyer in Illinois. He was best known for being elected as the 16th President of the United States of America. As president, Lincoln guided the United States through one of the worst times in American history, the Civil War. From the start of his political career, Lincoln was instrumental in his efforts and eventual success in ending slavery in America. He was known for his public speaking abilities and delivered some of the most popular speeches in United States history. He lived a successful life before the presidency, during the presidency, and up to the time of his tragic death. His life was cut short when he was assassinated in 1865 while still serving as President of the United States. Lincoln was revered as one of the greatest presidents in American history. Prior to becoming one of the most powerful men in the world, Lincoln grew up in a poverty-stricken family.
... we see that life is a façade; the characters disguise their sorrow in modesty. Joyce’s portrayal of Ireland undoubtedly creates a desire to evade a gloomy life.
from 1860 to 1865 (Wilson, 1). From humble upbringings to becoming the most powerful man in America, "Honest Abe" is known today as a great and influential person whose message echoes in American politics as well as American ethics. Lincoln is almost always voted the best or near-best President among historians (Wilson, 1). He helped mend the rift between the Union and the Confederacy, reuniting and reconstructing America and leading the way for his successors to tum this land ofthe free and home of the brave into the powerhouse it is today (Fetzer, 310). From his log cabin childhood to his tragic death, Abraham Lincoln was a great man whose legend lives on today.
Abraham had a lot of qualities that he relied on to leave is mark in the history. He was determined and ready to reach is goal no matter the difficulties. "It would have been no surprise if Lincoln never amounted to much in his life due to the various difficulties he faced."P16.He learned from his mistakes and make all his possible to avoid them in the future. "Lincoln was honest enough to admit his own personal failings regarding military leadership at the outset, but his strength was his ability to not only learn from his mistakes, but also to go ahead and study in order to develop his skills."P181. Abraham Lincoln had the advantage as an agent of change to know what the majority of the population is going through, and to understand them.
The Effects of Gravity There are some people who worry when they're outside, if they don't keep a good grip on the ground, they'll just go flinging off into space. They needn't really worry. about this, because gravity generally keeps that sort of thing from happening. The thing is, no one is really sure what causes gravity, but the effects have been studied by many. physicists and astronomers of the world.