OUTFLOW-INFALL INTERACTIONS AS A MECHANISM FOR TERMINATING ACCRETION IN PROTOSTARS

The formation of stars begins with the collapse of a dense interstella r cloud core to a protostar surrounded by a disk of gas and dust. Mate rial in the envelope of the cloud core falls inwards to feed further g rowth of the protostar and its accretion disk. At some point during th e accretion phase, an outflow of gas begins along the disk's rotation axis. Outflows have been studied in a large number of sources', and re cently it has become possible to study infall land outflow) very close to the star(2-8). But the possible interaction between these flows an d its effect on the mass of the disk and the young star remain uncerta in. Here we present observational evidence for an interaction between infalling and outflowing molecular gas. The opening angle of the outfl ow cone is largest near the star, indicating a widening of the outflow with time. Outside the lobes of the outflowing gas we see a narrow, d isk-like region that is infalling. We suggest that the widening of the outflow may isolate the disk from further infall.