Assessing the Formation of Solid Hydrogen Objects in Starless Molecular
  Cloud Cores
  The properties of the first-discovered interstellar object (ISO), 1I/2017
(`Oumuamua), differ from both Solar System asteroids and comets, casting doubt
on a protoplanetary disk origin. In this study, we investigate the possibility
that it formed with a substantial H2 ice component in the starless core of a
giant molecular cloud. While interstellar solid hydrogen has yet to be
detected, this constituent would explain a number of the ISO's properties. We
consider the relevant processes required to build decameter-sized, solid
hydrogen bodies and assess the plausibility of growth in various size regimes.
Via an energy balance argument, we find that the most severe barrier to
formation is the extremely low temperature required for the favorability of
molecular hydrogen ice. However, if deposition occurs, we find that the
turbulence within starless cores is conducive for growth into kilometer-sized
bodies on sufficiently short timescales. Then, we analyze mass loss in the
interstellar medium and determine the necessary size for a hydrogen object to
survive a journey to the Solar System as a function of ISO age. Finally, we
discuss the implications if the H2 explanation is correct, and we assess the
future prospects of ISO science. If hydrogen ice ISOs do exist, our
hypothesized formation pathway would require a small population of porous, 100
micron dust in a starless core region that has cooled to 2.8K via adiabatic
expansion of the surrounding gas and excellent shielding from electromagnetic
radiation and cosmic rays.
