Extended Data Fig. 4: Vorticity and perpendicular mach number in the rotating frame.
From: Breaking waves on the surface of the heartbeat star MACHO 80.7443.1718

A vortex sheet marks the shear layer in the l = 1 g-mode. This shear interface becomes corrugated and breaks when the mach number in the rotating frame is on the order of unity. The associated dissipation drives the spin up of the outer stellar layers.