Is GW170817 a Multimessenger Neutron Star-Primordial Black Hole Merger?
  We investigate the possibility of the gravitational-wave event GW170817 being
a light, solar-mass black hole (BH) - neutron star (NS) merger. We explore two
exotic scenarios involving primordial black holes (PBH) that could produce such
an event, taking into account available observational information on NGC 4993.
First, we entertain the possibility of dynamical NS-PBH binary formation where
a solar-mass PBH and a NS form a binary through gravitational interaction. We
find that while dynamical NS-PBH formation could account for the GW170817
event, the rate is highly dependent on unknown density contrast factors and
could potentially be affected by galaxy mergers. We also find that PBH-PBH
binaries would likely have a larger merger rate, assuming the density contrast
boost factor of an order similar to the NS-PBH case. These exotic merger
formations could provide new channels to account for the volumetric rate of
compact-object mergers reported by LIGO/Virgo. Secondly, we consider the case
where one of the NS's in a binary NS system is imploded by a microscopic PBH.
We find that the predicted rate for NS implosion into a BH is very small, at
least for the specific environment of NGC 4993. We point out that similar
existing (e.g. GW190425 and GW190814) and future observations will shed
additional light on these scenarios.
