Spinup and Disruption of Interstellar Asteroids by Mechanical Torques,
  and Implications for 1I/2017 U1 (`Oumuamua)
  The discovery of the first interstellar asteroid, 1I/2017 U1 (`Oumuamua), has
opened a new era for research on interstellar objects. In this paper, we study
the rotational dynamics of interstellar asteroids (ISAs) of irregular shapes
moving through the interstellar gas. We find that regular mechanical torques
resulting from the bombardment of gas flow on the irregular body could be
important for the dynamics and destruction of ISAs. Mechanical torques can spin
up the ISA, resulting in the breakup of the original ISA into small binary
asteroids when the rotation rate exceeds the critical frequency. We find that
the breakup timescale is short for ISAs of highly irregular shapes and low
tensile strength. We apply our results to the first observed ISA, `Oumuamua,
and suggest that its extreme elongated shape may originate from a reassembly of
the binary fragments due to gravity along its journey in the interstellar
medium. The tumbling of `Oumuamua could have been induced by rotational
disruption due to mechanical torques. Finally, we discuss the survival
possibility of high-velocity asteroids presumably formed by tidal disruption of
planetary systems by the black hole at the Galactic center.
