  We demonstrate that shadows cast on a proto-planetary disk can drive it
eccentric. Stellar irradiation dominates heating across much of these disks, so
an uneven illumination can have interesting dynamical effects. Here, we focus
on transition disks. We carry out 3D Athena++ simulations, using a constant
thermal relaxation time to describe the disk's response to changing stellar
illumination. We find that an asymmetric shadow, a feature commonly observed in
real disks, perturbs the radial pressure gradient and distorts the fluid
streamlines into a set of twisted ellipses. Interactions between these
streamlines have a range of consequences. For a narrow ring, an asymmetric
shadow can sharply truncate its inner edge, possibly explaining the steep
density drop-offs observed in some disks and obviating the need for massive
perturbers. For a wide ring, such a shadow can dismantle it into two (or
possibly more) eccentric rings. These rings continuously exert torque on each
other and drive gas accretion at a healthy rate, even in the absence of disk
viscosity. Signatures of such twisted eccentric rings may have already been
observed as, e.g., twisted velocity maps inside gas cavities. We advocate for
more targeted observations, and for a better understanding on the origin of
such shadows.
