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physical object > natural object > particle > hypothetical particle > dark matter > massive compact halo object > black hole

black hole
subject			fact

black hole	has antonym white hole
	has definition An object that is maximally gravitationally collapsed, and from which not even light can escape.
	has definition An object with such a strong gravitational field that even light cannot escape. Matter can fall into a black hole, but according to classical physics no matter or energy can leave it. (Hawking has used quantum theory to show that black holes emit blackbody radiation, but the effect is significant only for black holes much smaller than those that are expected to form by the collapse of stars, which have masses of several solar masses or more.)
	has definition A mass that is sufficiently compact that not even light can escape its intense gravity. Thus it appears black from the outside. If the sun were compressed to a sphere about four miles in diameter, it would become a black hole. It is believed that some massive stars, after exhausting their nuclear fuel, collapse under their own weight to form black holes.
	has definition A singularity in space, surrounded by an event horizon, caused by the collapse of a small but massively dense star through the effects of its own increasing gravity. By the time the state of singularity is reached, the remnants of the star may be minimal, but the gravitational force is so strong it prevents even light from escaping. Black holes may form the "power centers" of galaxies, thus explaining infrared radiation detected in several galactic centres. The properties of matter entering a black hole are the theme of John Wheeler's no hair theorem.
	has definition A gravitationally collapsed mass inside the Schwarzschild radius (q.v.), from which no light, matter, or signal of any kind can escape. A black hole occurs when the escape velocity of a body becomes the velocity of light (2GM / R = c2). If an object with the mass of the Sun had a radius of 2.5 km, it would be a black hole. Black holes represent one of the possible endpoints of stellar evolution for stars very much more massive than the Chandrasekhar limit.
	is a kind of singularity
	is a kind of massive compact halo object
massive compact halo object	is a part of halo
	has acronym MACHO
dark matter	is a part of dark halo
	has synonym hidden mass
hypothetical particle	has acceptance status hypothetical
physical object	has location or center of gravity
	has angular momentum
	has mass
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material
particle	obeys uncertainty principle
	has frequency inversely proportional to the wavelength
	has wavelength inversely proportional to its momentum
	has charge
	has mass

Kinds of black hole :

• extremal black hole (2 facts) - Black hole endowed with the maximal amount of force charge possible for a given total mass.
• Kerr black hole (2 facts) - A rotating, axisymmetric black hole based on Kerr's 1963 solution to Einstein's field equations.
• massive black hole (2 facts) - Utilized in a theoretical model for quasars and active galactic nuclei, according to which the energy source is due to infall (and resultant heating) of gas and stars onto a supermassive central black hole.
• massless black hole (2 facts) - In string theory, a particular kind of black hole that may have large mass initially, but that becomes ever lighter as a piece of the Calabi-Yau portion of space shrinks. When the portion of space has shrunk down to a point, the initially massive black hole has no remaining mass - it is massless. In this state, it no longer manifests such usual black hole properties as an event horizon.
• mini black hole (2 facts) - In a chaotic early universe, black holes may form at eras as early as the Planck time. The characteristic size of these mini black holes is 10^-6 gram, the minimum mass of a collapsing inhomogeneity at that time. Larger mini black holes may form at later eras. Since conventional theories of stellar evolution show that only very massive stars can form black holes, the possible formation of mini black holes is a unique characteristic of the very early universe.
• primordial black hole (2 facts) - Small black hole hypothesized to have formed during the first 10^-43 seconds of the universe, when quantum effects were very large.
• Schwarzschild black hole (2 facts) - A nonrotating, spherically symmetric black hole derived from Karl Schwarzchild's 1916 exact solution to Einstein's vacuum field equations.

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