Present-Day Star Formation: Protostellar Outflows and Clustered Star Formation

TL;DR

This paper reviews recent theoretical and observational advances in understanding how protostellar outflows influence star formation within dense, turbulent molecular cloud clumps, highlighting their role in maintaining turbulence and regulating star formation rates.

Contribution

It provides a synthesis of recent simulation and observational results emphasizing the importance of protostellar outflows in cluster formation processes.

Findings

Protostellar outflows sustain turbulence in cluster-forming clumps.

Star formation occurs over several free-fall times in dense clumps.

Massive stars form via filamentary accretion streams influenced by outflows.

Abstract

Stars form predominantly in clusters inside dense clumps of turbulent, magnetized molecular clouds. The typical size and mass of the cluster-forming clumps are \sim 1 pc and \sim 10^2 - 10^3 M_\odot, respectively. Here, we discuss some recent progress on theoretical and observational studies of clustered star formation in such parsec-scale clumps with emphasis on the role of protostellar outflow feedback. Recent simulations indicate that protostellar outflow feedback can maintain supersonic turbulence in a cluster-forming clump, and the clump can keep a virial equilibrium long after the initial turbulence has decayed away. In the clumps, star formation proceeds relatively slowly; it continues for at least several global free-fall times of the parent dense clump (t_{ff}\sim a few x 10^5 yr). The most massive star in the clump is formed at the bottom of the clump gravitational potential well at later times through the filamentary mass accretion streams that are broken up by the outflows from low-mass cluster members. Observations of molecular outflows in nearby cluster-forming clumps appear to support the outflow-regulated cluster formation model.