At the very dawn of our Universe, black holes could have formed in a way very different from the currently known. At least some theories say so. And the evidence to support them, as it turns out, may be lurking just around the corner.
Primordial black holes and their traces
Imagine the formation of a black hole, and you probably envision a massive star running out of fuel and collapsing on itself. However, the chaotic conditions of the early Universe may also have allowed many small black holes to form long before the first stars appeared.
These primordial black holes have been theorized to have existed for decades and could even be the ever elusive dark matter, the invisible matter that accounts for 85% of the total mass of the Universe.
No primordial black holes have been observed so far
A theoretical study to be published in the December issue of Physics of the Dark Universe argues that the primordial black hole trapped in a large rocky object in space would have swallowed its liquid core and left it hollow. On the other hand, a faster primordial black hole could leave behind straight tunnels large enough to be seen in a microscope if it passes through solid material, including material right here on Earth.
“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,” says study co-author Dejan Stojkovic, Ph.D., a professor of physics in the College of Arts and Sciences at the University of Buffalo. “We have to think outside of the box because what has been done to find primordial black holes previously hasn’t worked.”
The study calculated how big a hollow planetoid could be without collapsing and the probability that a primordial black hole would pass through an object on Earth.
Search for traces of black holes in hollow objects
When the Universe expanded rapidly after the Big Bang, certain regions of space may have been denser than their surroundings, causing them to collapse and form primordial black holes (PBHs).
PBHs would have much less mass than the stellar black holes that later formed from dying stars, but they would still be extremely dense, like the mass of a mountain compressed into an area the size of an atom.
Stojkovic, who has previously suggested where to look for theoretical wormholes, wonders if the PBH was trapped by a planet, moon, or asteroid during or after its formation.
“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,” Stojkovic says.
If the object collides with an asteroid, the PBH could fly out of the asteroid, leaving behind nothing but an empty shell.
But would such a shell be strong enough to support itself, or would it simply collapse under its own tension? By comparing the strength of natural materials such as granite and iron to surface tension and surface density, the researchers calculated that such a hollow object could be no more than one-tenth the radius of Earth, making it more like a small planet than a real planet.
“If it is any bigger than that, it’s going to collapse,” Stojkovic says.
These hollow objects can be detected with telescopes. The mass, and therefore the density, can be determined by studying the object’s orbit.
Everyday objects can be black hole detectors
According to the study, for objects without a liquid core, black holes can simply pass through them and leave behind a straight tunnel. For example, a black hole with a mass of 1022 grams would leave behind a tunnel 0.1 micron thick.
A large slab of metal or other material could serve as an effective black hole detector, tracking the sudden appearance of these tunnels, but Stojovich says the chances of finding existing tunnels in very old materials —from buildings hundreds of years old to rocks billions of years old — would be greater.
However, even assuming that dark matter is indeed composed of PBH, they calculated that the probability of PBH passing through a billion-year-old boulder is 0.000001.
Consequently, the likelihood of a PBH passing through you during your lifetime is low, to put it mildly. Even if it did, you probably wouldn’t notice it.
Unlike rock, human tissue has little tension, so the PBH will not tear it apart. Although the kinetic energy of the PBH can be enormous, it cannot release much energy during the collision because it moves very fast.
Need for a new theoretical framework
Theoretical studies like this one are crucial, Stojkovic says, noting that many physical concepts which once seemed implausible are now considered plausible.
Now the industry, Stojkovic adds, faces some serious challenges, among them dark matter. The last major revolutions in the field — quantum mechanics and the general theory of relativity — are now a century old.
“The smartest people on the planet have been working on these problems for 80 years and have not solved them yet,” he says. “We don’t need a straightforward extension of the existing models. We probably need a completely new framework altogether.”
Provided by phys.org
