The Black holeis a region of spacetimefrom which gravity prevents anything, including light, from escaping. [ 1 ]The theory of general relativitypredicts that a sufficiently compact masswill deform spacetime to form a black hole. Around a black hole, there is a mathematically defined surface called an event horizonthat marks the point of no return. The hole is called black because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black bodyin thermodynamics. [ 2 ] [ 3 ] Quantum field theory in curved spacetimepredicts that event horizons emit radiationlike a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar massor greater. Objects whose gravity fieldsare too strong for light to escape were first considered in the 18th century by John Michelland Pierre- Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschildin 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelsteinin 1958. Long considered a mathematical curiosity, it was during the 1960s that theoretical work showed black holes were a generic prediction of general relativity. The discovery of neutron starssparked interest in gravitationally collapsedcompact objects as a possible astrophysical reality. Black holes of stellar massare expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holesof millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies. Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matterand with electromagnetic radiationsuch as light. Matter falling onto a black hole can form an accretion diskheated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a black hole, their orbit can be used to determine its mass and location. These data can be used to exclude possible alternatives (such as neutron stars). In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the core of our Milky Waygalaxy contains a supermassive black hole of about 4.3 million solar masses
Posted on: Fri, 29 Nov 2013 06:06:16 +0000
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