Star Formation

In the last couple of decades, astronomers have developed a partial understanding of the basic physical processes by which stars form within molecular clouds. The gravitational collapse of rotating dense "cores" results in the creation of a central protostar surrounded by a flattened, spinning "accretion disk" of gaseous material with dimensions comparable to the solar system. As the forming young stellar object (YSO) evolves, most of the material is transported inward through the accretion disk. Some is ejected outward in spectacular bipolar jets which sweep up molecular material and become observable at millimeter wavelengths.

The outflows carry away angular momentum, thus enabling the central protostar to grow in mass. Eventually, physical conditions in the disk become conducive to the agglomeration of micron-size dust grains into km-size planetesimals and later, into planet-size bodies. At this point, the disk accretion phase ends, leaving behind a fully-formed star surrounded by a forming planetary system. UMass astronomers have played a major role in contributing to the evolution of this paradigm. Currently, UMass faculty and students are focusing theoretical and observational programs on the following fundamental questions: What are the major differences between the physical mechanisms of the birth of low-mass and high-mass stars? How should our simplistic picture of isolated star formation be modified to account for the more complex processes that produce stars in clusters or occur when collapse is triggered by various environmental effects. What are the observational signatures that distinguish the various modes of star formation. How do stars evolve from their earliest highly embedded stage to the more revealed pre-main sequence phase? How are bipolar jets and molecular outflows launched? How much energy, momentum and turbulence is deposited into the parent molecular cloud from the forming protostellar system? Observational work include studies of molecular clouds and cores; high resolution molecular spectroscopy of dense molecular tracers that highlight regions of infall and outflow; millimeter and submillimeter continuum mapping of molecular cloud cores; and high resolution imaging of highly embedded and revealed young stellar objects. These projects make use of a variety of telescopes and instruments ranging from those available locally (the FCRAO 14-m), to millimeter interferometers such as OVRO and BIMA, submillimeter telescopes such as the HHT and JCMT, and space-borne instruments such as SWAS.