When you think of black holes, you probably imagine massive stars collapsing under their own gravity.
But scientists have long theorized the existence of primordial black holes (PBHs)—tiny black holes that may have formed during the chaotic conditions of the early universe, long before stars were born.
These PBHs could even be the mysterious dark matter that makes up 85% of the universe’s mass.
Despite decades of research, no one has ever observed a primordial black hole.
A new study from the University at Buffalo offers fresh ideas for where to look, suggesting PBHs might leave detectable signatures in planets or even everyday materials like rocks and metal.
Hollow planets and tiny tunnels
The study, published in Physics of the Dark Universe, proposes two ways PBHs might reveal themselves.
Hollow Planets or Moons
If a primordial black hole became trapped inside a planet, moon, or asteroid, it could consume the liquid core of the object, leaving behind a hollow shell. The researchers calculated that such a hollow structure could only survive if it were no larger than one-tenth of Earth’s radius—likely making it a small planet or moon.
These hollow objects could be detected by telescopes. By measuring their mass and density through their orbits, scientists could identify objects with densities too low for their size, indicating they might be hollow.
Microscopic Tunnels in Materials
A PBH traveling through solid material, such as rock or metal, could leave behind a straight tunnel about 0.1 microns thick (1,000 times smaller than a human hair). Researchers suggest examining very old materials, like ancient rocks or centuries-old metal structures, for these tiny tunnels.
What are the chances?
While the likelihood of finding these signs is extremely small, the potential discovery of PBHs would be groundbreaking. The study calculated that even if PBHs make up dark matter, the chance of one passing through a billion-year-old rock is about 1 in a million.
Thankfully, if a PBH were to pass through a person, it wouldn’t be dangerous. Unlike rocks or metal, human tissue wouldn’t tear apart because it lacks strong structural tension, and the black hole would move too fast to release much energy.
Finding evidence of primordial black holes could solve some of the biggest mysteries in physics, including the nature of dark matter. As study co-author Dejan Stojkovic explains, solving these puzzles might require new theories beyond our current understanding.
“The smartest people have been working on these problems for decades,” he says. “It’s time to think outside the box.”
