Ultrahigh-energy Gamma Rays and Gravitational Waves from Primordial
  Exotic Stellar Bubbles
  We put forward a novel class of exotic celestial objects that can be produced
through phase transitions occurred in the primordial Universe. These objects
appear as bubbles of stellar sizes and can be dominated by primordial black
holes (PBHs). We report that, due to the processes of Hawking radiation and
binary evolution of PBHs inside these stellar bubbles, both electromagnetic and
gravitational radiations can be emitted that are featured on the gamma-ray
spectra and stochastic gravitational waves (GWs). Our results reveal that,
depending on the mass distribution, the exotic stellar bubbles consisting of
PBHs provide not only a decent fit for the ultrahigh-energy gamma-ray spectrum
reported by the recent LHAASO experiment, but also predict GW signals that are
expected to be tested by the forthcoming GW surveys.
