Probing the dynamics of persistent leading structures in non-relativistic astrophysical jet experiments

An astrophysical jet is a commonly observed astronomical phenomenon driven by the dynamics of accretion disks. Jets have complex spatial structures but typically can be distinguished by a collimated region, a jet head which is the leading edge of the outflows, and regions affected by and surrounding the jet. Although there are a variety of unique shapes for each jet object, one can find from experiments and astrophysical objects that the leading head is not merely an extension of the trailing collimated column having self-similar structures. In Caltech Jet Experiments wherein we simulate non-relativistic astrophysical jets, a reproducible persistent jet head structure is observed for a wide range of operating conditions. This configuration is observed from jets with heavy ions (Ar or N) but not clearly from hydrogen jets which can be interpreted as light ions fast dynamics impede the self-organized states. From a recently developed polarimeter, measurements of line-integrated emissions can be resolved in sub-mm scale. The spectra from the polarimeter provide electron density, fluid velocity, temperature, and order of magnitude of B-field information. Our measurements suggest that the jet head is characterized by a localized high density front with possible indication of reversed flow on the periphery, and the following bulged structure. Based on experimental observations, research is underway to describe the self-organized structure of the jet head using the magnetohydrodynamic framework.