Micro black hole

Micro black holes, also called quantum mechanical black holes or mini black holes, are hypothetical tiny black holes, for which quantum mechanical effects play an important role.

In 1971, Hawking introduced the idea that black holes may exist that are smaller than stellar mass, 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. They might be observed by astrophysicists in the near future, through the particles they are expected to emit by Hawking radiation.

Some hypotheses involving additional space dimensions predict that micro black holes could be formed at energies as low as the TeV range, which are available in particle accelerators such as the LHC (Large Hadron Collider). Popular concerns have then been raised over end-of-the-world scenarios (see Safety of particle collisions at the Large Hadron Collider). However, such quantum black holes would instantly evaporate, either totally or leaving only a very weakly interacting residue. Beside the theoretical arguments, the cosmic rays hitting the Earth do not produce any damage, although they reach center of mass energies in the range of hundreds of TeV.

In principle, a black hole can have any mass equal to or above the Planck mass (about 22 micrograms). 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, ${\displaystyle R=2GM/c^{2}}$, where G is the gravitational constant, c is the speed of light, and M the mass of the black hole. On the other hand, the Compton wavelength, ${\displaystyle \lambda =h/Mc}$, 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 reduced Compton wavelength (${\displaystyle \lambda \;=\;\hbar /Mc}$, where ħ is the reduced planck constant) exceeds half the Schwarzschild radius, and no black hole description exists. This smallest mass for a black hole is thus approximately the Planck mass.

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