Physics 321
Astrophysics II:  Lecture #12
Prof. Dale E. Gary

Formation of Protostars

Star Formation

Basic Picture

Clouds of gas and dust collapse and form Young Stellar Objects (YSOs), sometimes visible and sometimes enshrouded in dust.  The relevant physics of the collapse includes Thus, we can expect a cloud of typical size 0.1 pc to collapse over perhaps 1 million years, and when it reaches stellar size it should be spinning very rapidly and be highly magnetized.  This is exactly what is observed, except that the spin rate and magnetic field strength are somewhat less than predicted by these simple arguments.  Our best understanding of the reason for the discrepancy is that the strong magnetic fields themselves slow down the rotation rate by coupling the spinning core to the outer disk, and dynamical processes cause the proto-stellar object to shed some of its mass and much of its magnetic field.
Observational Evidence