In section 6. Interstellar and circumstellar matter
Evidence for a massive dust-trapping vortex connected to spirals: a multi-wavelength analysis of the HD 135344B protoplanetary disk
Scattered-light observations of protoplanetary disks often show spiral arms, rings, and large scale asymmetries. Some of the disks with scattered-light spiral arms also have asymmetric millimeter-sized dust emission. To explain these structures embedded planets are usually invoked, but none has been firmly detected to date. New high-resolution ALMA observations and archival data of the HD 135344B disk has firmly identify an azimuthal shift with wavelength of its emission peak, which suggests that the asymmetry denotes a dust-trapping vortex. This vortex in turn would launch the two spiral arms seen in scattered light. This alternative mechanism will need confirmation by higher-resolution observations and more detailed simulations, but it nevertheless provides a potential explanation of the observed asymetries and would imply a later formation of at least the outer planets in protoplanetary disks.