Astro-seminar by Heather Johnston: Dispersal of Protoplanetary Discs via External Photoevaporation

Unveiling how protoplanetary discs disperse and transition into debris discs is crucial to our understanding of the diverse disc and exoplanet populations.  Dust-rich debris discs are commonly observed around stars of various masses and ages.  The dust in these discs is continuously replenished by ongoing planetesimal collisions, analogous to our own Kuiper belt.  In the high irradiation environments of massive star-forming regions (SFRs), where the majority of planet formation is thought to occur, external photoevaporation also contributes to rapid dispersal of discs.  This may play a fundamental role in triggering planetesimal formation via the streaming instability at the disc outer edge and thus shaping the architecture of a debris disc. We use the dust and gas evolution code DustPy in tandem with external photoevaporation FUV prescription (FRIED grid) and planetary torque-induced dust traps to explore how narrow substructures in protoplanetary discs might evolve into the broad dust belts observed in debris discs over 15 Myr.   We find that strong external photoevaporation naturally leads to planetesimal formation, with the inner edge of the planetesimal belt corresponding to the disc truncation radius, which is very sensitive to the strength of the external photoevaporation. The strength of the FUV radiation, therefore, directly influences the width of planetesimal belts.  Lastly, we find that relatively high levels of external FUV (>100 G0) could be a viable mechanism to create wide planetesimal belts at large orbital radii.