Black holes are often imagined as the remnants of massive stars that collapse under their own gravity. But new research suggests that the chaotic conditions of the early universe may have given birth to smaller, primordial black holes (PBHs) long before the first stars formed. These theoretical objects might not only help explain dark matter but could also be hiding in surprising places — from hollow planets to everyday objects on Earth.
Primordial black holes have been theorized for decades, yet they remain undetected. A new study, co-led by researchers from the University at Buffalo, proposes innovative ways to search for their elusive signatures. The findings, soon to be published in Physics of the Dark Universe, suggest PBHs could leave traces ranging from hollow planetoids in space to microscopic tunnels in solid materials like rocks, metals, or even glass.
What Makes PBHs Unique?
Unlike stellar black holes, which are formed by collapsing stars, PBHs could have originated during the rapid expansion of the universe after the Big Bang. Regions of space that were denser than their surroundings may have collapsed to form these ultra-dense objects, with the mass of a mountain compacted into an area the size of an atom.
Hollow Planetoids in Space
The study suggests that if a PBH were trapped inside a celestial body with a liquid core, such as a planet or moon, it could consume the core and leave a hollow shell behind. These hollow objects, though small—no larger than one-tenth of Earth’s radius—could theoretically sustain themselves without collapsing. Their unusually low density for their size might make them detectable through their orbital properties.
Microscopic Tunnels on Earth
For solid objects without liquid cores, PBHs might pass through, leaving behind straight microscopic tunnels. These tunnels could theoretically be identified in very old materials, such as ancient rocks or metal slabs. For instance, a PBH with a mass of 10²² grams would create a tunnel just 0.1 microns wide. While the likelihood of a PBH passing through a billion-year-old boulder is exceptionally low (0.000001), the cost of searching for these tunnels is minimal, making it a worthwhile endeavor.
Should We Worry About PBHs?
Despite their incredible density and kinetic energy, PBHs pose no threat to humans. If a PBH were to pass through a person, it would leave no noticeable damage, as human tissue lacks the tension to interact with the black hole’s energy.
Revolutionizing Our Understanding of the Universe
This study highlights the need for innovative theoretical frameworks to address some of astrophysics’ biggest unanswered questions, such as the nature of dark matter. Co-author Dejan Stojkovic emphasizes the importance of thinking beyond traditional models:
“We don’t need a straightforward extension of existing theories. We probably need a completely new framework altogether.”
As research on primordial black holes continues, it holds the potential to unlock new insights into the early universe, dark matter, and the fundamental forces that shape our cosmos.
