A swarm of tiny ice balls is scattered across a warm room. Some melt faster, others slower, but when only wet spots remain, they all vanish in the same way: the last drop evaporates according to the same law. This is roughly how primordial black holes behave — hypothetical objects born in the first moments after the big bang. The lightest of them have long been living their final seconds, and their ultimate evaporation follows a universal scenario.
This scenario is dictated by a simple balance: as much mass as goes out as radiation, that much the hole loses. The energy flux discovered by Stephen Hawking is like an invisible wind carrying particles away from the surface. When a hole becomes very light, its radiation forms a characteristic spectrum — a smoothly declining 'tail' whose shape does not depend on the original sizes of the holes. But if new, unknown particles appear, this wind changes direction: the spectrum develops dips and bumps, like potholes appearing on a smooth road.
The authors of the study showed that such distortions can be detected even if primordial black holes make up only a small fraction of all dark matter. Future gamma-ray telescopes, sensitive to high energies, will be able to 'feel' this tail. If data reveals a deviation from the smooth universal shape, it would signal the existence of new particles not predicted by the Standard Model of physics.
Thus, tiny, almost evaporated black holes become a natural laboratory for searching the invisible. Their last breath, a gamma-ray burst, could tell us what our world is truly made of.
A primordial black hole with a mass of about a billion tons (like a small asteroid) would be the size of an atomic nucleus and would evaporate over a time comparable to the age of the universe.
In Dan Simmons' novel 'Hyperion', black holes on humanity's service are used as energy sources, and their evaporation as a weapon.