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Micro black hole
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- MBH redirects here. It can also refer to the Hayist Bases Movement, or a unit of power - a thousand BTUs per hour.
Micro black holes, are tiny hypothetical black holes also called quantum mechanical black holes or mini black holes, for which quantum mechanical effects play an important role. In principle, a black hole can have any mass significantly above the Planck mass. In 1974 Stephen Hawking argued that due to quantum effects, such black holes "evaporate" by a process now referred to as Hawking Radiation in which elementary particles (photons, electrons, quarks, gluons, etc.) are emitted. His calculations show that the smaller the size of the black hole, the faster the evaporation rate, resulting in a sudden burst of particles as the micro black hole suddenly explodes. It is possible that such quantum primordial black holes were created in the high-density environment of the early universe (or big bang), or possibly through subsequent phase transitions.
Primordial black holes of initial masses around 1015 grams would be completing their evaporation today; lighter primoridal black holes would have already evaporated. In optimistic circumstances, the Fermi Gamma-ray Space Telescope satellite, launched in June 2008, might detect experimental evidence for evaporation of nearby black holes by observing gamma ray bursts. [It is unlikely that a collision between a microscopic black hole and an object such as a star or a planet would be noticeable. This is due to the fact that the small radius and high density of the black hole would allow it to pass straight through any object consisting of normal atoms, interacting with only few (or even none) of its atoms while doing so.]
In familiar three-dimensional gravity, available technologies do not reach the minimum Planck mass required to produce a black hole. However, in scenarios where there are extra dimensions of space in certain special configurations such as large extra dimensions, special cases of the Randall-Sundrum model, and String theory configurations like the GKP solutions, the Planck mass can be as low as the TeV range. In these circumstances, it was argued in 2001 that black hole production could be an important and very visible effect at the Large Hadron Collider (LHC) or future higher-energy colliders. Hawking's calculation and more general quantum mechanical arguments predict that these black holes decay almost instantaneously into a spray of particles that could be seen by detectors at these facilities.
Explanation
Smallest possible black hole
To make a black hole one must concentrate mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of light. This condition gives the Schwarzschild radius, , where G is Newton's constant and c is the speed of light, as the size of a black hole of mass M. On the other hand, the Compton wavelength, , where h is Planck's constant, represents a limit on the minimum size of the region in which a mass M at rest can be localized.
For sufficiently small M, the Compton wavelength exceeds the Schwarzschild radius, and no black hole description exists. This smallest mass for a black hole is thus approximately the Planck mass, which is about 2 × 10-8 kg or 1.2 × 1019 GeV/c2.
Any primordial black holes of sufficiently low mass will Hawking evaporate to near the Planck mass within the lifetime of the universe. In this process, these small black holes radiate away matter. A rough picture of this is that pairs of virtual particles emerge from the vacuum near the event horizon, with one member of a pair being captured, and the other escaping the vicinity of the black hole. The net result that the black hole loses mass [due to conservation of energy]. According to the formulae of black hole thermodynamics, the more the black hole loses mass the hotter it becomes, and the faster it evaporates, until it approaches the Planck mass. At this stage a black hole would have a Hawking temperature of TP / 8p (5.6×1032 K), which means an emitted Hawking particle would have an energy comparable to the mass of the black hole. Thus a thermodynamic description breaks down. Such a mini-black hole would also have an entropy of only 4p nats, approximately the minimum possible value.
At this point then, the object can no longer be described as a classical black hole, and Hawking's calculations also break down. Conjectures for the final fate of the black hole include total evaporation, or production of a Planck mass-sized black hole remnant. If intuitions about quantum black holes are correct, then close to the Planck mass the number of possible quantum states of the black hole is expected to become so few and so quantised that its interactions are likely to be quenched out. It is possible that such Planck-mass black holes, no longer able either to absorb energy gravitationally like a Classical black hole because of the quantised gaps between their allowed energy levels, nor to emit Hawking particles for the same reason, may in effect be stable objects. They would in effect be WIMP's, weakly interacting massive particles, possibly this could explain dark matter.
Creation of micro black holes
Production of a black hole requires concentration of mass or energy within the corresponding Schwarzschild radius. In familiar three-dimensional gravity, the minimum such energy is 1019 GeV, which would have to be condensed into a region of approximate size 10-33 cm. This is far beyond the limits of any current technology; the Large hadron collider has a design energy of 14 TeV. This is also beyond the range of known collisions of cosmic rays with Earth's atmosphere, which reach center of mass energies in the range of hundreds of TeV. It is estimated that to collide two particles to within a distance of a Planck length with currently achievable magnetic field strengths would require a ring accelerator about 1000 light years in diameter to keep the particles on track.
Stephen Hawking also said in chapter 6 of his Brief History of Time that physicist John Wheeler once calculated that a very powerful hydrogen bomb using all the deuterium in all the water on Earth could also generate such a black hole, but Hawking does not provide this calculation or any reference to it to support this assertion.
Some extensions of present physics posit the existence of extra dimensions of space. In higher-dimensional spacetime, the strength of gravity increases more rapidly with decreasing distance than in three dimensions. With certain special configurations of the extra dimensions, this effect can lower the Planck scale to the TeV range. Examples of such extensions include large extra dimensions, special cases of the Randall-Sundrum model, and String theory configurations like the GKP solutions. In such scenarios, black hole production could possibly be an important and observable effect at the LHC.
Stable micro black holes?
While Hawking radiation is sometimes questioned, Leonard Susskind summarizes an expert perspective in his recent book: "Every so often, a physics paper will appear claiming that black holes don't evaporate. Such papers quickly disappear into the infinite junk heap of fringe ideas." Popular concerns have been raised over end-of-the-world scenarios; see Safety of particle collisions at the Large Hadron Collider. Additional safety arguments beyond those based on Hawking radiation were given in the paper (see also ), which showed that in hypothetical scenarios with stable black holes that could damage Earth, such black holes would have been produced by cosmic rays and have already destroyed known astronomical objects such as the Earth, Sun, neutron stars, or white dwarfs.
Fiction
- In David Brin's novel Earth a manmade micro blackhole slips into the core of the earth.
- In the short story How We Lost the Moon, A True Story by Frank W. Allen, which is actually written by Paul J. McAuley, a micro black hole is accidentally created on the moon, which gradually consumes it.
- Larry Niven's Hugo Award-winning short story The Hole Man deals with a "quantum black hole".
- In the Guyver manga, it is one of the weapons used by Guyver Exceed.
- In John Reed's literary satire, "The Whole," or "Duh Whole" (published by Simon & Schuster/Pocket Books/MTV Books), a small black hole appears in the middle of the United States, proceeds to engulf four states, and is still growing, at novel's end.
- In The Warlock Unlocked, monks of the order of Saint Vidicon on Christopher Stasheff's Gramarye think they may be able to create one, but do not because of the steep gravity gradient.
External links
- A. Barrau & J. Grain, : a review of the searches for new physics with micro black holes possibly formed at colliders
- - Space.com
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