In section 6. Interstellar and circumstellar matter
Gaps, rings, and non-axisymmetric structures in protoplanetary disks: Emission from large grains
The famous ALMA image of HL Tau is often interpreted as tracing the presence of a system of planets embedded in this young circumstellar disk. These would open gaps and form the system of low-brightness rings seen in the images. However, Flock et al. propose a different explanation: the system of rings could simply be the result of relatively modest density fluctuations in the gas disk coupled to a significant concentration of centimeter-sized dust at density maxima. These fluctuations would be created by Rossby waves triggered at the outer edge of a dead zone located at about 20 au. These waves also trigger vortexes that can break up the rings and concentrate the dust particles azimuthally. The model thus predicts that along with ring structures, vortexes should also be observed in young disks.