If you shrank an ordinary black hole to the size of a grain of sand, it would shine like a tiny star and quickly vanish in a flash. That's Stephen Hawking's prediction: the event horizon acts like a hot surface emitting particles. The smaller the hole, the higher its temperature, and vice versa — giant black holes at the centers of galaxies are colder than the cosmic microwave background.

But what if gravity is more intricate than Einstein's theory suggests? In some models, the usual geometry is augmented with terms involving higher powers of curvature, as if you added extra layers with different elasticity to a simple rubber sheet. Such black holes are called Lovelock black holes, and they have a branch where the geometry looks particularly clean. The authors of the study measured how much radiation escapes from such objects and found something astonishing: a Lovelock hole of the same size as an ordinary one turns out to be far more 'silent.'

The secret lies in temperature. The horizon of a Lovelock hole is colder: thermal motion near the surface freezes, making it harder for particles to escape. The increased transparency doesn't help — the energy flux is set by temperature alone. Moreover, as the order of the theory (the number N) increases, the radiation almost entirely shifts to the scalar channel — the one associated with the simplest spinless particles. The electromagnetic component fades, and the hole 'speaks' only one language.

Such a sharp drop in power is not just a numerical curiosity. If such objects exist in nature, their evaporation could be so weak that we might never detect a flash from a dying microscopic black hole. On the other hand, the very dependence of the spectrum on the order N provides a clean observational signature — if we ever manage to catch a signal from quantum evaporation, the shape of the spectrum will immediately tell us which theory of gravity we are dealing with.