Jets in protostellar systems

Bipolar outflows and highly collimated jets are associated with young stellar objects of all masses. The evidence shows that they are produced in the earliest phases of star formation and continue for as long as accretion discs around the protostars are present. in this review, we discuss the observational, theoretical, and numerical work that has been done to explore protostellar jets. in particular, we analyze the foundations of the theory of centrifugally driven disc winds which appears to be a successful model for the acceleration and collimation of protostellar jets. We then discuss the recent progress with 2-D numerical MHD simulations of disc winds and jets. These simulations show that both stationary, as well as episodic jets are produced, depending upon the mass loading of the outflow. The disc wind phenomenon also appears to be robust; it is independent of the details of the magnetic configuration of accretion discs.