Externally Fed Accretion onto Protostars

Abstract

The asymmetric molecular emission lines from dense cores reveal slow, inward motion in the clouds' outer regions. This motion is present both before and after the formation of a central star. Motivated by these observations, we revisit the classic problem of steady, spherical accretion of gas onto a gravitating point mass, but now include self-gravity of the gas and impose a finite, subsonic velocity as the outer boundary condition. We find that the accretion rate onto the protostar is lower than values obtained for isolated, collapsing clouds, by a factor that is the Mach number of the outer flow. Moreover, the region of infall surrounding the protostar spreads out more slowly, at a speed close to the subsonic, incoming velocity. Our calculation, while highly idealized, provides insight into two longstanding problems -- the surprisingly low accretion luminosities of even the most deeply embedded stellar sources, and the failure so far to detect spatially extended, supersonic infall within their parent dense cores. Indeed, the observed subsonic contraction in the outer regions of dense cores following star formation appears to rule out a purely hydrodynamic origin for these clouds.

accepted by MNRAS

References in corpus (5)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• Driven and Decaying Turbulence Simulations of Low-Mass Star Formation: From Clumps to Cores to Protostars
• Protostar Formation in Supersonic Flows: Growth and Collapse of Spherical Cores
• Formation and Collapse of Quiescent Cloud Cores Induced by Dynamic Compressions
• The Approach to Collapse of Molecular Clouds

Cited by in corpus (4)

• The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds
• From forced collapse to H ii region expansion in Mon R2: Envelope density structure and age determination with Herschel
• Origin of the dense core mass function in contracting filaments
• Externally Fed Star Formation: A Numerical Study