Black hole

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An artists rendintion of a black hole.
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A Black Hole is a region of space in which the gravitational field is so powerful that nothing can escape after it has pasted the event horizon of the Black Hole. The reason it is called a Black hole is that even light is unable to escape it. Black holes can be detected, when a black hole interacts with matter out-side of the event horizon a large amount of radiation emits from it. Black holes are currently understood by Einsteins general theory of relativity, which was formed in 1916. The idea of an object with a gravitational pull strong enough to prevent light escaping from it was first thought of in the 18th century. Einsteins theory predicts that when a large enough amount of mass is present within a sufficiently small region of space, all paths through space are warped inwards towards the center of the volume, forving all matter and radiation to fall inward. While general relativity describes a black hole as a region of empty space with a pointlike singularity at the center and an event horizon at the outer edge, the description changes when the effects of quantum mechanics are taken into account. Research on this subject indicates that, rather than holding captured matter forever, black holes may slowly leak a form of thermal energy called Hawking radiation. However, the final, correct description of black holes, requiring a theory of quantum gravity, is unknown.Black holes can have any mass. Since the gravitational force of a body on itself, at the surface of a body of any shape, increases in inverse proportion to its characteristic lengthscale squared (as volume-2/3 ), an object of any shape and mass that is sufficiently compressed will collapse under its own gravity and form a black hole. However, when black holes form naturally, only a few mass ranges are realistic.

There are 4 catrgories of black holes:

  • Supermassive black holes contain millions to billion times the mass of the sun and it is belived that in the center of a black hole is located at the center of most galaxys, that includes our own milky way. Active Galactis Nuclei is thought to be from them.
  • Intermediate-mass black holes, whose size is measured in thousands of solar massesm may exist. these black holes have been propossed to be the power source of Ultra-Luminous X ray Sources.
  • Stellar-mass black holes have masses ranging from about 1.5 - 3.0 solar masses to 15 solar masses. These black holes are generaly created by the collapse of indivual stars. 20+solar mass stars may collapse to form black holes.
  • Micro black holes, which have masses at which the effects of quantum mechanics are expected to become very important. This is usually assumed to be near the Planck mass. Alternatively, the term micro black hole or mini black hole may refer to any black hole with mass much less than that of a star. Black holes of this type have been proposed to have formed during the Big Bang (primordial black holes), but no such holes have been detected as of 2008.

There are two theorys on how Micro black holes might be produced. They are as follows.

The Big Bang, which produced pressures far larger than that of a supernove and therefore sufficient to procude primordial black holes without needing the powerful gravity fields of collapsing large stars. High-energy paticle accelerators such a the LHC (large hardon Collider), if certain non-standard assumptions are all correct. However, any black holes produced in such a matter could evaporate near instantaneously, this means there is no danger.

General relativity describes mass as changing the shape of spacetime, and the shape of spacetime as describing how matter moves through space. For objects much less dense than black holes, this results in something similar to Newton's laws of gravity: objects with mass attract each other, but it's possible to define an escape velocity which allows a test object to leave the gravitational field of any large object. For objects as dense as black holes, this stops being the case. The effort required to leave the hole becomes infinite, with no escape velocity definable.

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