Astrophysical implications of hypothetical stable TeV-scale black holes

We analyze the macroscopic effects of TeV-scale black holes that might be created at the LHC, as predicted in some scenarios with large extra dimensions, under the extremely conservative hypothesis that such black holes are stable and might accrete matter. We extract the most stringent bounds by studying the effects of black holes produced by cosmic rays striking much denser objects, in particular white dwarfs and neutron stars. Their existence and observed properties place strong constraints on the possible production and accretion of such black holes. We conclude that there is no risk of any significance whatsoever from such black holes.

A black hole produced in an LHC collision and trapped inside the Earth would accrete matter only very slowly, because of its tiny size. The relevant question is the timescale: would it grow large enough to cause macroscopic damage within the remaining lifetime of the Sun? We classify the extra-dimensional accretion scenarios into two cases.

For scenarios in which a trapped black hole could in principle accrete on a timescale shorter than the lifetime of the Sun, we show the scenario is already excluded by astrophysics. The key observation is that cosmic rays produce exactly the same black holes when they strike other bodies in the universe. A high-energy cosmic ray hitting a white dwarf or a neutron star would create such black holes, and because those bodies are vastly denser than the Earth, the black holes would be captured and would begin to accrete. If these black holes could grow fast enough to be dangerous, they would already have destroyed observed white dwarfs and neutron stars on timescales far shorter than those objects' observed ages.

A possible objection is that cosmic-ray black holes are produced moving at high velocity and would pass through a body, whereas LHC black holes could be produced nearly at rest and remain trapped. The paper addresses this directly: while high-velocity production is true for ordinary matter, charged black holes and black holes produced in certain configurations would be stopped inside white dwarfs and neutron stars regardless. The enormous density and gravitational binding of these bodies guarantees capture of a sufficient population to make the argument work. Once captured, a cosmic-ray-produced black hole inside a neutron star would accrete from a far denser medium than the Earth could ever provide, so any dangerous growth rate would have manifested as the destruction of these stars long ago.

Combining the strong theoretical expectation that any micro black hole evaporates essentially instantly via Hawking radiation with the empirical, model-independent bound from the observed stability of white dwarfs and neutron stars, we find that there is no risk of any significance whatsoever from black holes that might be produced at the LHC. The astrophysical bound stands even if Hawking radiation is assumed not to operate at all.