Primordial Black Holes from First-Order Cosmological Phase Transitions

Understand

We discuss the possibility of forming primordial black holes during a first-order phase transition in the early Universe.

• As is well known, such a phase transition proceeds through the formation of true-vacuum bubbles in a Universe that is still in a false vacuum.
• When there is a particle species whose mass increases significantly during the phase transition, transmission of the corresponding particles through the advancing bubble walls is suppressed.
• Consequently, an overdensity can build up in front of the walls and become sufficiently large to trigger primordial black hole formation.