Creation of a black hole bomb instability in an electromagnetic system

The amplification and generation of electromagnetic radiation by a rotating metallic or lossy cylinder, first proposed by Zel'dovich in the 1970s, is closely linked to quantum friction, energy extraction from rotating black holes, and runaway mechanisms such as black hole bombs. Although advances such as acoustic analogs of the Zel'dovich effect and the observation of negative resistance in low-frequency electromagnetic models have been reported, genuine positive signal gain, spontaneous emission of electromagnetic waves, and runaway amplification have not previously been verified. Here, we provide the first experimental demonstration that a mechanically rotating metallic cylinder acts as an amplifier of a rotating electromagnetic field mode. Moreover, when combined with a low-loss resonator, the system becomes unstable and operates as a generator seeded only by noise. The exponential runaway amplification of spontaneously generated electromagnetic modes is observed, establishing the electromagnetic analog of the Press-Teukolsky black hole bomb and paving the way to experimental tests of quantum friction from vacuum fluctuations.