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Abstract

Do Evaporating Black Holes Form Photospheres and/or Chromospheres?

Several authors have claimed that the observable Hawking emission from a microscopic black hole is significantly modified by the formation of a photosphere or chromosphere around the black hole due to QED or QCD interactions between the emitted particles. Analyzing these models we identify a number of physical and geometrical effects which invalidate these scenarios. In all cases, we find that the observational signatures of a cosmic or Galactic halo background of primordial black holes or an individual black hole remain essentially those of the standard Hawking model, with little change to the detection probability. We note, though, that inner bremsstrahlung photons generated by charged particles as they accelerate away from the black hole dominate over the direct Hawking emission of photons at low photon frequencies.

Sensitivity of the Fermi Detectors to Gamma-Ray Bursts from Evaporating Primordial Black Holes (PBHs)

Primordial Black Holes (PBHs), which may have been created in the early Universe, are predicted to be detectable by their Hawking radiation. PBHs with an initial mass of ~ 5 x 10^14 g should be expiring today with a burst of high energy particles including gamma-rays. Evaporating PBHs are candidate progenitors of unidentified non-repeating Gamma-Ray Bursts (GRBs). We propose spectral lag, which is the temporal delay between the high and low energy pulses, as a possible method to identify PBH evaporation events with the Fermi Gamma-ray Space Telescope Observatory detectors.

Generalized Second Law limits on the Variation of Fundamental Constants

The maximal time variation in the electronic charge permitted by the Generalized Second Law of Thermodynamics applied to black holes radiating in the cosmic microwave background matches the value of the variation in the fine structure constant measured by Webb et al.. Does accretion by charged black holes give a stronger or weaker constraint?

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