Primordial black holes and short gamma-ray bursts

The possible existence of primordial black holes (PBHs) has long been a key observational question. At present, the only known way to detect low-mass ones (below 10(15) g) is through the Hawking radiation process. This radiation in turn depends on the nature of hadron interactions in the 100 MeV region and beyond. In the case of a first-order quantum-chromodynamics phase transition, we expect a sharp burst of gamma rays from the PBH. We have pointed out that there is a class of gamma-ray bursts that have this property and could provide evidence for PBHs in the galaxy. Future study of these events is crucial. Recently, we have shown that a diffuse gamma-ray glow should exist in the halo from these PBHs. There now seems to be evidence for this effect as well. (C) 1998 Elsevier Science B.V. All rights reserved.