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Alex Vilenkin
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Black holes from cosmic inflation
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Vacuum bubbles may nucleate during the inflationary
epoch and expand, reaching relativistic speeds.
After inflation ends, the bubbles are quickly
slowed down, transferring their momentum
to surrounding matter. The ultimate fate
of the bubble depends on its size. Bubbles
smaller than certain critical size collapse
to ordinary black holes, while in the supercritical
case the bubble interior inflates, forming
a baby universe, which is connected to the
exterior region by a wormhole. The wormhole
then closes up, turning into two black holes
at its two mouths. The resulting black hole
mass spectrum is extremely broad, ranging
over many orders of magnitude. For some parameter
values, these black holes can serve as seeds
for supermassive black holes and may account
for LIGO observations.

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