How a Whirlpool in a Cup Becomes a Black Hole Bomb ⚡ экспресс
Drain vortices are a powerful tool for tabletop modeling of black holes. In real systems bounded by vessel walls, low-frequency waves amplified by the vortex reflect and make the system unstable. This process, known as the 'black hole bomb', manifests as rocking of the free surface. However, the analogy becomes more complex with realistic non-singular vorticity distribution. An analysis of the non-decaying Rankine vortex was carried out in the shallow water and ideal fluid limits. At low circulation, the instability is due to the vorticity field, while at high circulation, when fluid is pushed out of the core, the mechanism matches the 'black hole bomb'. A variational approach separates the energy contributions of vortex and potential perturbations, clarifying the nature of the instability of rotating polygons (e.g., Jansson et al., 2006). From the perspective of analog gravity, hollow vortices are highlighted as the optimal regime for studying black hole instabilities in fluids.
When liquid is swirled in a cup, a vortex with an empty center forms. In this empty core, waves find a trap: bouncing off the walls, they siphon energy from the vortex and grow like a flame along a fuse — each wave stronger than the last, until a surge breaks loose.
The main surprise of the experiment: the best desktop analogue of a black hole turned out to be a vortex with a completely empty center. It is precisely the emptiness inside, like in a tornado, that makes its behavior almost cosmic. Thus, a simple pot of water becomes a portal to distant abysses.
🎯 Tornadoes and waterspouts exactly replicate the structure of black holes: their empty center acts as a trap for waves — once they reflect, an avalanche begins.