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Books: Black Hole
 An Introduction To Black Holes, Information And The String Theory Revolution: The Holographic Universe 
 Black Holes: An Introduction 
 Black Holes and Time Warps: Einstein's Outrageous Legacy (Commonwealth Fund Book Program) 
 The Edge of Infinity: Supermassive Black Holes in the Universe 
 Exploring Black Holes: Introduction to General Relativity 
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Universe Mysteries: Black Hole
Cosmic body with gravity (see gravitation) so intense that nothing, not even light, can escape. It is suspected to form in the death and collapse of a star that has retained at least three times the Sun's mass. Stars with less mass evolve into white dwarf stars or neutron stars. Details of a black hole's structure are calculated from Albert Einstein's general theory of relativity: a "singularity" of zero volume and infinite density pulls in all matter and energy that comes within an event horizon, defined by the Schwarzschild radius, around it. Black holes cannot be observed directly because they are small and emit no light. However, their enormous gravitational fields affect nearby matter, which is drawn in and emits X rays as it collides at high speed outside the event horizon. Some black holes may have nonstellar origins. Astronomers speculate that supermassive black holes at the centres of quasars and many galaxies are the source of energetic activity that is observed. Stephen W. Hawking theorized the creation of numerous tiny black holes, possibly no more massive than an asteroid, during the big bang. These primordial "mini black holes" lose mass over time and disappear as a result of Hawking radiation. Although black holes remain theoretical, the case for their existence is supported by many observations of phenomena that match their predicted effects. History about Black HoleThe concept of a body so massive that not even light could escape was put forward by the English geologist John Michell in a 1783 paper sent to the Royal Society. At that time, the Newtonian theory of gravity and the concept of escape velocity were well known. Michell computed that a body with 500 times the radius of the Sun and of the same density would have, at its surface, an escape velocity equal to the speed of light, and therefore would be invisible. In his words:
Although he thought it unlikely, Michell considered the possibility that many such objects that cannot be seen might be present in the cosmos. In 1796, the French mathematician Pierre-Simon Laplace promoted the same idea in the first and second edition of his book Exposition du Systeme du Monde. It disappeared in later editions. The whole idea gained little attention in the 19th century, since light was thought to be a massless wave, not influenced by gravity. In 1915, Einstein developed the theory of gravity called General Relativity. Earlier he had shown that gravity does influence light. A few months later, Karl Schwarzschild gave the solution for the gravitational field of a point mass, showing that something we now call a black hole could theoretically exist. The Schwarzschild radius is now known to be the radius of the event horizon of a non-rotating black hole, but this was not well understood at that time. Schwarzschild himself thought it was not physical. In the 1920s, Subrahmanyan Chandrasekhar argued that special relativity demonstrated that a non-radiating body above 1.44 solar masses, now known as the Chandrasekhar limit, would collapse since there was nothing known at that time that could stop it from doing so. His arguments were opposed by Arthur Eddington, who believed that something would inevitably stop the collapse. Both were correct, since a white dwarf more massive than the Chandrasekhar limit will collapse into a neutron star. However, a neutron star above about three solar masses will itself become unstable against collapse due to similar physics. In 1939, Robert Oppenheimer and H. Snyder predicted that massive stars could undergo a dramatic gravitational collapse. Black holes could, in principle, be formed in nature. Such objects for a while were called frozen stars since the collapse would be observed to rapidly slow down and become heavily redshifted near the Schwarzschild radius. The mathematics showed that an outside observer would see the surface of the star frozen in time at the instant where it crosses that radius. However, these hypothetical objects were not the topic of much interest until the late 1960s. Most physicists believed that they were a peculiar feature of the highly symmetric solution found by Schwarzschild, and that objects collapsing in nature would not form black holes. Interest in black holes was rekindled in 1967 because of theoretical and experimental progress. Stephen Hawking and Roger Penrose proved that black holes are a generic feature in Einstein's theory of gravity, and cannot be avoided in some collapsing objects. Interest was renewed in the astronomical community with the discovery of pulsars. Shortly thereafter, the use of the expression "black hole" was coined by theoretical physicist John Wheeler.[1] The older Newtonian objects of Michell and Laplace are often referred to as "dark stars" to distinguish them from the "black holes" of general relativity. Black Hole External LinksBlack Holes FAQs Net Advance of Physics: Black Holes Primordial Black Holes Introduction to Black Holes APOD Index Virginia Tech: Black Holes Black Holes Andrew Hamilton's Homepage Black Holes and Neutron Stars Black Holes by Gabor Kunstatter Universe Today Supermassive Black Holes Jillian's Guide to Black Holes What is a black hole? How is it formed? Astronomers Discover 'Middleweight' Black Holes - The field of black holes, formerly dominated by heavyweights packing the gravitational punch of a billion Suns and lightweights just a few times heavier than our Sun, now has a new contender... Black Hole T-Symmetry Violation Creation of Black Hole Detected by Robert Roy Britt |
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Black Holes- Birth, Life & Death - According to the most recent theories, black holes are the consequence of the "death" of a big star, which is, minimum, 3 times as massive as the sun. The gravitational pull of such an object is so big, that neither light, nor any other kind of electromagnetic radiation, can escape. Black Holes - Black holes are peculiar objects with many strange properties, but most books and articles have emphasised their exotic aspects, and obscured their fundamentally simple nature. |
Time Travel Portal: Black Holes - A massive astrophysical object that is theorized to be created from the collapse of a neutron star. The gravitational forces are so strong in a black hole that they overcome neutron degeneracy pressure and, roughly speaking, collapse to a point (known as a singularity). |
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