The mass of the black hole dwindles, and the space around it trembles. In 1974, Stephen Hawking showed that black holes evaporate due to quantum particles that pop up right at the edge. But it turns out that even without these particles, a dying hole can make its presence heard. If magnetic field lines thread through it, the change in spacetime curvature makes the field oscillate and spit out electromagnetic waves. It’s like an antenna that radiates when it shakes — only here the antenna is the black hole itself, and the ‘shaking’ comes from mass loss under gravity. The geometry of a non-rotating hole was first described by Karl Schwarzschild way back in 1916.

When scientists applied the laws of electrodynamics in curved space, they found that the radiation is extremely weak but precisely predictable. Its spectrum is ‘red’—the lower the frequency, the more energy it carries. The peak occurs at waves whose period matches the hole’s lifetime. And primordial black holes, tiny ones born in the early universe, might just emit very slow waves that we could still try to catch. So a dying black hole turns into a transmitter, its signal adding a fresh page to the story of its evaporation.