Water flowing through a pipe can become a trap for sound. If the flow speed exceeds the speed of sound in water, then sound waves trying to go against the current can no longer escape: they are swept away, like light beyond a black hole's horizon. This is not just a metaphor: in such analog systems, particles akin to Hawking radiation are indeed born.
The authors considered a trickier case — when the speed of waves depends on their wavelength, and short waves can move faster than sound. It turns out that a horizon still emerges, but not where the flow speed matches the speed of sound, but deeper, where it catches up with the faster waves. Using an elegant mathematical trick, the S-matrix near the horizon, they calculated how many particles are born and compared the results with the tunneling method. Both approaches agreed: the spectrum turned out to be almost thermal, with a temperature set by the effective surface gravity of the new horizon.
This means that Hawking radiation is not a quirk of strictly relativistic physics but a general property of media with horizons. Even if familiar laws change at extremely small distances, black holes will still 'shine.' And analog experiments with fluids or light in the lab gain a solid theoretical foundation.
In 1981, Bill Unruh showed that sound waves in a moving fluid behave like light in curved spacetime. Since then, physicists have tried to create a 'sonic black hole' in the lab to catch its analog of Hawking radiation.
In Stanislaw Lem's novel 'Fiasco,' astronauts use analog models to understand the properties of alien civilizations — much like physicists model black holes in fluids.