When you think about how a black hole forms, you probably picture a huge star running out of energy and collapsing in on itself. But did you know that the wild conditions right after the Big Bang might have created many tiny black holes long before any stars even existed?
These so-called primordial black holes have been a topic of speculation for quite some time, and they might even be connected to dark matter—the mysterious stuff that makes up about 85% of the universe’s mass but remains invisible to us.
The catch? No one has actually seen one yet.
A new study, co-led by researchers from the University at Buffalo, suggests we should broaden our search approach—considering both big and small possibilities—to find evidence of these elusive objects.
The researchers propose that signs of primordial black holes could show up as large hollow planetoids floating in space or tiny microscopic tunnels in everyday materials here on Earth, like rocks or metals.
This theoretical work is set to appear in the December issue of *Physics of the Dark Universe* but is already available online.
The idea is that if a primordial black hole got trapped inside a large rocky body in space, it could devour its liquid core and leave behind a hollow shell.
On the other hand, if it moved quickly enough through solid material, it might create straight tunnels that could be spotted under a microscope—even right here on Earth!
While it’s unlikely we’ll stumble upon these signatures easily, looking for them doesn’t demand much resource investment, explains Dejan Stojkovic, Ph.D., one of the study’s authors and a professor at UB. The potential reward—finding evidence for primordial black holes—would be huge!
The research also looked into how big these hollow planetoids could get without collapsing and assessed how likely it is for one to pass through an object on Earth.
And don’t worry: If you’re concerned about a primordial black hole zooming through you, rest assured—it wouldn’t be deadly! Co-author De-Chang Dai from National Dong Hwa University and Case Western Reserve University notes that due to these slim chances, they’re concentrating on solid markers that have been around for thousands or even billions of years.
Hollow objects can’t exceed one-tenth the size of Earth.
After the Big Bang, the universe was expanding at a crazy pace, and some regions of space might have ended up denser than their surroundings.
This could have led to the formation of primordial black holes (PBHs). Unlike the black holes that form from dying stars, which are much more massive, PBHs are significantly lighter but still incredibly dense—imagine cramming the mass of a mountain into something as small as an atom!
Stojkovic, who has some interesting ideas about where to find theoretical wormholes, started thinking: what if a PBH got caught inside a planet, moon, or asteroid during its creation or afterward?
He suggests that if this object has a liquid core, then the PBH could actually absorb that liquid because it’s denser than the solid outer layer. If something like an asteroid were to hit it later on, the PBH might just escape and leave behind a hollow shell.
But here’s the kicker: would that shell be strong enough to hold itself together? Or would it cave in under its own weight?
By comparing materials like granite and iron with factors like surface tension and density, researchers figured out that these hollow objects can’t be larger than one-tenth of Earth’s radius.
So they’re more likely to be minor planets rather than full-fledged planets. Stojkovic points out that anything bigger would probably collapse in on itself.
The cool part is that these hollow structures could actually be spotted with telescopes! By looking at how an object orbits, we can figure out its mass and density.
Stojkovic notes that if an object’s density seems too low for its size, that’s a pretty good hint that it’s hollow inside!
You know, everyday items might actually work as detectors for black holes!
The study suggests that primordial black holes (PBHs) might just zip right through solid objects that don’t have a liquid core, creating a straight tunnel as they go.
For instance, if you had a PBH weighing around 10²² grams, it would carve out a tunnel that’s just 0.1 microns wide. You could use something like a big metal slab as a black hole detector by keeping an eye out for these sudden tunnels appearing.
However, Stojkovic mentions that you’re more likely to find existing tunnels in really old materials—like buildings that are centuries old or rocks that have been around for billions of years.
That said, even if dark matter is made up of PBHs, they figured out that the chance of one passing through an ancient boulder is only about 0.000001. You have to weigh the cost against the benefit, Stojkovic points out. Does it cost much to look for these? Not really.
So, the odds of encountering a PBH during your lifetime are pretty slim—if you did happen to cross paths with one, you probably wouldn’t even notice it! Human tissue has some give to it, unlike rock, so a PBH wouldn’t rip through you like it would with stone.
Plus, even though a PBH has massive kinetic energy, it doesn’t lose much of it when colliding because it’s moving at such high speeds. When something travels faster than sound through another material, Stojkovic explains, the molecules don’t have time to react.
Think about throwing a rock through glass—it’ll break into pieces—but shoot at the glass with a bullet and all you’ll get is a clean hole!
We really need to come up with some fresh theoretical ideas.
Stojkovic emphasizes the importance of theoretical research like this, pointing out that many ideas in physics that once seemed far-fetched are now taken seriously. He mentions that the field is grappling with significant challenges, including the mystery of dark matter.
It’s been a hundred years since we had major breakthroughs like quantum mechanics and general relativity. The brightest minds have been tackling these issues for 80 years without finding solutions, he notes.
What we really need isn’t just an easy upgrade to our current models; it’s likely time for a totally new approach.