1BlackHoles

= ** Black Holes ** =

The Universe's Ying
A black hole is an object of such immense gravity that everything around it gets pulled in and never escapes including light. Formed from a dying star a black hole is formed when the star runs out of it's steady supply of fuel and can no longer keep up its expansive force. Gravity then takes over by pulling everything in increasing in density and gravitational pull.



As the star shrinks it will be become something else depending on its mass; less massive it may turn into a white dwarf, a more massive star may become a supernova, if the mass of the star is less then three times the sun then it will form a neutron star. However if the star happens to be more than three times the mass of the sun then nothing stands in the way of it collapsing without limit to an indefinitely small size and infinitely large density, a point called the "singularity", as shown by Robert Oppenheimer and Hartland S. Snyder. At the point of singularity the rules of [|Einstein's general theory of relativity] becomes important. the theory states that space curves around matter, the more dense the matter the more space curves. When the star shrinks below a certain size in accordance to it's mass, the extreme curvature of space seals off all contact. The point beyond which nothing can escape is called the event horizon, and its radius is called the Schwarzschild radius Beyond this point nothing can be seen by the eyes of mankind.



Due to the fact that light and other forms of energy can never escape a black hole they can not be observed directly, only indirectly. This is accomplished by observing the effects of it's gravitational pull on near by objects or by the x-rays and radio frequency signals emitted by the swirling matter being pulled into the black hole. Only a small number of black holes have possibly been discovered, the first being Cygnus X-1 in 1971.

During the big bang, some regions of space might have become so compressed that they formed //primordial black holes.// These black holes would not be completely black, because radiation could still ‘tunnel out’ of the event horizon at a steady rate, leading to the evaporation of the hole. Primordial black holes could therefore be very hot. It is also believed that there is no set mass a black hole can have ranging from; mini-black holes (10e-10 solar masses) to supermassive black holes which can be infinitely massive. A supermassive black hole is defined as a black hole formed from the collapse of an object, such as a massive gas cloud, significantly more massive than typical stars. By supermassive astronomers usually mean greater than 10e5 solar masses. Such objects can increase their mass by accreting material from their surroundings, and the energy released in this process may be responsible for the activity seen in galaxies and [|quasars]. In addition, there is good evidence for a supermassive black hole of 3–4 million solar masses at the center of our Galaxy.There are several theoretically possible forms of black hole. A non-rotating black hole without electrical charge is known as a //Schwarzschild black hole//. A non-rotating black hole with electrical charge is termed a //Reissner–Nordström black hole// after the German physicist Hans Jacob Reissner and Finn Gunnar Nordström. In practice, black holes are likely to be rotating and uncharged, a form known as a Kerr black hole. Black holes are not entirely black; theory suggests that they can emit energy in the form of [|Hawking radiation].

Contrary to popular myth, a black hole is not a cosmic vacuum cleaner. If our Sun was suddenly replaced with a black hole of the same mass, the earth's orbit around the Sun would be unchanged. (Of course the Earth's temperature would change, and there would be no solar wind or solar magnetic storms affecting us.) To be "sucked" into a black hole, one has to cross inside the Schwarzschild radius. At this radius, the escape speed is equal to the speed of light, and once light passes through, even it cannot escape.The Schwarzschild radius can be calculated using the equation for escape speed. vesc = (2GM/R)1/2 For photons, or objects with no mass, you can substitute c (the speed of light) for Vesc and find the Schwarzschild radius, R, to be R = 2GM/c2 If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole at the center of our solar system.

media type="google" key="3869172164167982669&hl=en&fs=true" width="487" height="398" Sam Neill talks about black holes.

The Universe's Yang
White holes may be a part of the vacuum solution to Einstein's field equations describing a Schwarzschild wormhole. One end of this type of wormhole is a black hole, sucking stuff in, and the other is a white hole, spewing stuff out.This gives us the idea that black holes in the universe connect to white holes somewhere else, this is untrue, for two reasons. First, Schwarzschild wormholes are unstable, disconnecting as soon as they form. Second, Schwarzschild wormholes are only one solution to the Einstein field equations in vacuum (when no matter interacts with the hole). Real black holes are formed by the collapse of stars, so it can't connect to anything.