Observation of self-oscillating supersonic flow across an acoustic horizon in two dimensions

The authors create a spatially bounded supersonic region in a two-dimensional atomic superfluid, forming an acoustic analogue of a black-hole horizon. The observed superflow appears to be modulated by quasi-periodic bursts of superluminal signals. By measuring their frequencies, the authors find agreement with numerical simulations of soliton oscillation frequencies within the black-hole horizon, where solitons are emitted due to the Landau instability.