Seeing the invisible: indirect methods to detect the action of streaming instability

Protoplanetary discs – structures made of dust and gas surrounding newborn stars –are the planets’ birthplaces. According to the “core accretion” theory, planets form by growing the μm-sized dust grains present in discs up to the size of a planet. While the dust grains grow, they aerodynamically interact with the gas component of the disc; as a result, cm-sized grains rapidly drift towards the central star, hindering planet formation. A proposed solution to this issue is rapid dust concentration via streaming instability (SI). Probing the action of SI, however, is challenging because the formed substructures are too small to be directly observed. This work investigates the emission of systems undergoing SI, searching for detectable signatures. We simulated a set of systems undergoing SI and analysed their emission. We first focused on the global emission: by comparing the emission computed for the simulations (before and after the action of SI) to the data emission, we found that the action of SI drives the simulations towards the area of the plane occupied by the data. This suggests that dusty filaments formation via SI is consistent with the data. We then analysed asymmetries in the emission produced when systems undergoing streaming instability are observed at an inclination angle. Our analysis revealed that the inclined disc emission exhibits a maximum (minimum) emission along the minor (major) axis. We characterised such emission both qualitatively and quantitatively via a simplified analytical model, showing that the model can be used to detect the presence of SI.