FORMATION OF BLACK-HOLES IN FIRST-ORDER PHASE-TRANSITIONS IN THE UNIVERSE

A new mechanism is proposed for the formation of black holes in first- order phase transitions in the Universe. Collisions between the walls of bubbles of true vacuum are shown to give rise to an isolated region (a bag) of false vacuum between them, which collapses with a high pro bability into a black hole. Thus, primordial black holes become a sens itive indicator of phase transitions, and astronomical limitations on the spectrum of primordial black holes impose constraints on the param eters of phase transitions of the first kind in the Universe.