Physics and Astronomy Colloquium Series

Christopher DeVries

CSU Stanislaus

"The Simple Model:
Fitting analytic solutions of the equation transfer to
observations reveals infall rates for star-forming molecular
clouds"

Stars like the Sun form from molecular clouds with very low densities that can stretch over several parsecs in space. As part of the earliest phase of star
formation these clouds are compressed and begin to collapse into one or more dense stars under the influence of gravity. We can detect signs of molecular
cloud infall by looking for the blue-asymmetric spectral line infall signature at millimeter and submillimeter wavelengths. Unfortunately it is hard to determine the exact rate of infall, the parts of the clouds that are infalling, or the structure within the cloud without constructing an elaborate physical model and using a radiative transfer simulation to predict the radiation emitted from the modeled cloud. This sort of simulation can take many minutes or even hours to produce. By making a few simple assumptions it is possible to construct a model
collapsing cloud whose radiative emission can be analytically calculated in less than a second. These models are much easier to fit to observations, and are
remarkably accurate at gauging a cloud's infall rate. This is a case where, contrary to conventional wisdom, constructing a simple model and using proper assumptions yield better results than trying to construct the most physically realistic model possible.