Triggering Protostellar Collapse, Injection, and Disk Formation

Certain meteoritical inclusions contain evidence for the existence of short-lived radioactivities such as ²⁶Al and ⁴¹Ca at the time of their formation 4.566 billion years ago. Because the half-lives of these nuclides are so short, this evidence requires that no more than about a million years elapsed between their nucleosynthesis and their inclusion in cm-sized solids in the solar nebula. This abbreviated time span can be explained if these nuclides were synthesized in a stellar source such as a supernova, and were then transported across the interstellar medium by the resulting shock wave, which then triggered the gravitational collapse of the presolar molecular cloud core. Detailed 2D and 3D numerical hydrodynamical models are reviewed and show that such a scenario is consistent with the time scale constraint, and with the need to both trigger collapse and to inject shock-wave matter into the collapsing protostellar cloud and onto the protoplanetary disk formed by the collapse. This revised version was published online in June 2006 with corrections to the Cover Date.