Protostar Collapse

Abstract

Once magnetic forces have become dynamically unimportant, turbulence has decayed, and rotational effects have become unimportant relative to gravity in the core of a molecular cloud, and the mass of the core exceeds the thermal Jeans mass, gravitational collapse proceeds. Some of the questions that can be asked include (1) what are the initial conditions for collapse? (2) What is the physics that induces and maintains collapse? (3) What is the role of magnetic fields during collapse? (4) Can the embedded infrared sources (Class I objects) be identified with the stage of evolution just after disk formation? (5) What is the observational evidence for infall? (6) What is the origin of bipolar outflows? (7) Once a disk forms, how is angular momentum transported? (8) Will the core fragment or form a single star? (9) What fraction of the core mass ends up in the star? (10) How is the high-mass star formation problem solved? In fact, for high mass star formation, turbulence is important in the initial conditions, and the problem is considered in more detail in Chap. 5. The present chapter applies in general to low-mass star formation; however the physical regimes of the collapse itself, as described next, apply to all masses.