Time Varying Dynamical Star Formation Rate

TL;DR

This paper provides numerical evidence that self-gravity drives a superlinear, time-varying star formation rate in turbulent molecular clouds, challenging turbulence-only models and highlighting the importance of gravitational collapse.

Contribution

It demonstrates that self-gravity dominates early star formation dynamics, leading to superlinear growth and altered density and velocity structures in star-forming regions.

Findings

Star formation rate grows roughly as t^2 over time.

Self-gravity steepens density profiles and creates power-law tails.

Turbulent velocity profiles flatten in collapsing regions.

Abstract

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.