Time Varying Dynamical Star Formation Rate
  We present numerical evidence of dynamic star formation in which the accreted
stellar mass grows superlinearly with time, roughly as $t^2$. We perform
simulations of star formation in self-gravitating hydrodynamic and
magneto-hydrodynamic turbulence that is continuously driven. By turning the
self-gravity of the gas in the simulations on or off, we demonstrate that
self-gravity is the dominant physical effect setting the mass accretion rate at
early times before feedback effects take over, contrary to theories of
turbulence-regulated star formation. We find that gravitational collapse
steepens the density profile around stars, generating the power-law tail on
what is otherwise a lognormal density probability distribution function.
Furthermore, we find turbulent velocity profiles to flatten inside collapsing
regions, altering the size-linewidth relation. This local flattening reflects
enhancements of turbulent velocity on small scales, as verified by changes to
the velocity power spectra. Our results indicate that gas self-gravity
dynamically alters both density and velocity structures in clouds, giving rise
to a time-varying star formation rate. We find that a substantial fraction of
the gas that forms stars arrives via low density flows, as opposed to accreting
through high density filaments.
