These hypothetical objects — Primordial Black Holes — are thought to have formed within seconds of the Big Bang, during a time when the universe's material was densely packed.
In today’s universe, black holes typically form when massive stars—those at least 20 times the mass of our Sun—exhaust their nuclear fuel and collapse under their gravity. This process sets a lower size limit for stellar black holes.
Primordial black holes, however, belong to a different category. These hypothetical objects are thought to have formed within seconds of the Big Bang, during a time when the universe’s material was densely packed. According to NASA, in those chaotic early moments, “pockets of hot material may have been dense enough to form black holes, potentially with masses ranging from 100,000 times less than a paperclip to 100,000 times more than the Sun’s.” Once the universe expanded and cooled, these unique conditions ceased to exist.
Though primordial black holes have never been directly detected, they remain a tantalizing possibility. Some scientists have even speculated that they could make up dark matter—a mysterious substance accounting for a significant portion of the universe’s mass.
A Bold New Way to Hunt for PBHs
A recent study proposes an intriguing method to identify primordial black holes: searching for planets and asteroids that bear the marks of their passage. If PBHs exist and are roaming the cosmos, they might occasionally become ensnared by celestial bodies. If such a body has a liquid core, the black hole could consume this dense material, leaving behind a hollowed-out structure.
Physics professor Dejan Stojkovic from the University at Buffalo explains, “If the object has a liquid central core, then a captured PBH can absorb the liquid core, whose density is higher than the density of the outer solid layer.” Over time, such an object could become hollow, and the black hole might be ejected through an impact or other disturbance.
Interestingly, the study found that these hollow objects could remain stable under specific conditions. As long as their radius is less than one-tenth of Earth’s, the strength of natural materials like granite and iron could prevent collapse.
Other Interactions with PBHs
Not all interactions between PBHs and celestial bodies result in hollowed-out structures. If an asteroid is entirely solid, a passing PBH might create a straight tunnel without consuming any material. The presence of these linear tunnels could serve as another indicator of PBH activity.
“It is also possible that an object like an asteroid is completely solid without a liquid core. In that case, the interaction with a PBH will not result in [a] hollow sphere,” the team notes. Evidence of such tunnels could be a new clue in the hunt for these elusive black holes.
Earth and the Search for Evidence
While searching for PBH-induced signatures in space is a challenge, our planet might hold accessible clues. Tiny PBHs passing through Earth could leave behind minuscule tunnels. Scientists suggest examining old rocks, ancient structures, or even monitoring flat metal surfaces for new tunnels over time. Though the odds of finding these signatures are slim, the effort would require minimal resources and could yield revolutionary discoveries.
As Stojkovic highlights, “The chances of finding these signatures are small, but searching for them would not require much resources, and the potential payoff—the first evidence of a primordial black hole—would be immense.”
The study suggests that PBHs could theoretically pass through the human body without harm. Despite their immense kinetic energy, their interaction with human tissue would be negligible. “Since the tension of the human tissue is small, it will not tear the tissue apart,” the researchers explain.
Although this theory may seem speculative, it provides a new perspective on the nature of primordial black holes and how to detect them.
