The `beating heart': spontaneous oscillations of a sessile lens

When an oil drop is emplaced on a water surface, it takes the form of a sessile lens. When the oil contains water-insoluble surfactant, the lens radius may oscillate in a quasi-periodic fashion; when viewed from above, the sessile lens resembles a beating heart. We here elucidate the subtle mechanism responsible for this striking flow structure by presenting the results of our combined experimental and theoretical investigation.