Detectable universes inside regular black holes
  While spacetime in the vicinity outside astrophysical black holes is believed
to be well understood, the event horizon and the interior remain elusive. Here,
we discover a degenerate infinite spectrum of novel general relativity
solutions with the same mass-energy and entropy that describe a dark energy
universe inside an astrophysical black hole. This regular cosmological black
hole is stabilized by a finite tangential pressure applied on the dual
cosmological-black hole event horizon, localized up to a quantum indeterminacy.
We recover the Bekenstein-Hawking entropy formula from the classical fluid
entropy, calculated at a Tolman temperature equal to the cosmological horizon
temperature. We further calculate its gravitational quasi-normal modes. We find
that cosmological black holes are detectable by gravitational-wave experiments
operating within the $\mu{\rm Hz}-{\rm Hz}$ range, like LISA
space-interferometer.
