Uncovering the Episodic Nature of Star Formation and Revealing the Environment in which Stars and Planets Form

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The formation of a star and its planetary system are intimately coupled. Star formation commences when a localized region within a molecular cloud becomes gravitationally unstable, with the free-fall build-up of the protostar and its surrounding protoplanetary disk depending on both the distribution of the gas reservoir and its associated kinematics and spin. Theoretical calculations suggest that the majority of the protostellar mass arrives first onto the disk, predominantly mediated by angular momentum and magnetic fields, and must then reach the protostar via disk accretion mechanisms. It is within the circumstellar disk that planets are expected to form, and recent observations have provided spectacular images of disks with rings and gaps- furthering the suggestion that planet formation is both ubiquitous and active early in the lifetime of stars. Building on the pioneering observational work that my international research team has performed over the last four years using the JCMT and ALMA, my graduate students and I will monitor the submillimetre variability from more than one hundred deeply embedded (very young) protostars on monthly timescales in order to robustly determine the episodic nature of their mass assembly. These youngest protostars radiate primarily through the energy released during protostellar accretion from the disk. The bulk of this radiation is observed at far infrared and submillimetre wavelengths due to reprocessing of the starlight by dust in the enshrouding envelope. Thus, monitoring the submillimetre variability provides a direct measure of the underlying accretion history of the system. Already, we have revealed that many protostars are variable and uncovered an eighteen month periodic variable protostar (likely triggered due to a companion star or planet). Extending these observations over a full decade will therefore provide a large enough sample to enable robust statistical determinations of the frequency, amplitude, and duration of accretion variability and an analysis of the physical/chemical conditions under which individual protostars vary. As a whole, these measurements relate directly to the type(s) of accretion instability involved and their disk location(s). They therefore provide critical constraints on theoretical disk accretion hypotheses and inform planet formation models. A key goal of star formation studies is to determine the manner in which protostellar systems form, in order to understand the stellar initial mass function, stellar multiplicity, the formation of planetary systems, and possibly the origins of life. Our recent successful monitoring of deeply embedded protostars over multi-year timescales has provided a unique approach to determining the mass assembly of embedded protostars and the accretion physics within the inner protoplanetary disk. Thus, future instruments, e.g. CCAT-p, CMB S-4, SPICA, Origins, are anticipating using our time-domain techniques for key science projects.