New Structures in Galactic Disks: Predictions and Discoveries

Original paper can be found at http://www.astrosociety.org/pubs/cs/222-252.html--Copyright Astronomical Society of the Pacific --Our main goal is to review: 1) some physical mechanisms which form the observed structures in galactic disks; 2) the discovery of new galactic structures predicted earlier. Specifically in the first part of the paper we discuss some questions associated with spiral structure. The second part is devoted to the prediction and discovery of giant vortices in gaseous disks of the grand design spiral galaxies using method of reconstruction of the full three-component velocity field from the observed line-of-sight velocity field. In the third part, we give some arguments in favour of existence of the slow bars in the grand design spiral galaxies

Over-reflection in lab: the all-sufficient cause of instability of an annular supersonic shear in simulations on free-surface shallow water

Presented are results of the pioneering research on the over-reflection instability of an annular ‘supersonic’ shear in experiments on free-surface shallow water covering a differentially rotating and properly shaped bottom (characteristic waves on shallow water play the role of sound, all alternative shear instabilities are suppressed due to specificity of the rotation profile and experimental procedure). The consideration focuses upon distinctive features of the structures generated by the instability as perturbations of shallow-water thickness. The features of the structures observed are compared with those predicted by an original theory. The structures are also readily interpreted as a superposition of Huygens-Mach fronts that are multiply over-reflected from the shear, having been induced by a supersonic disturbance moving along it. Owing to the annular geometry, the instability in the experiments develops even in absence of external boundaries that are universally included in traditional theoretical schemes for feedback necessary for the wave generation

Gas motions in the plane of the spiral galaxy NGC 3631

Peer reviewe