Primordial black holes have been theorized for decades and may even be the eternally elusive dark matter. However, primordial black holes have not yet been observed. These tiny black holes could become trapped in rocky planets or asteroids, consuming their liquid cores from within and leaving hollow structures behind, according to a duo of astrophysicists from the University at Buffalo, Case Western Reserve University, and National Donghua University. It is said that there is. Alternatively, microtunnels could be left in very old rocks on Earth, or in the glass or other solid structures of very old buildings.

Small primordial black holes are perhaps the most intriguing and intriguing relics of the early universe.

They could act as candidates for dark matter, be sources of primordial gravitational waves, and help solve cosmological problems such as domain walls and the magnetic monopole problem.

However, so far no convincing primordial black hole candidates have been observed.

Professor Dejan Stojković of the University at Buffalo said: “Although the chances of finding these signatures are low, the search does not require many resources and the potential reward of providing the first evidence of a primordial black hole is enormous. It's going to become something.”

“We need to think outside the box because what has been done so far to find primordial black holes has not worked.”

Professor Stojkovic and colleague Dr. De Zhang Dai, of Case Western Reserve University and National Donghua University, are investigating how large hollow asteroids can grow without collapsing, and whether a primordial black hole is The probability of passing was calculated. Earth.

“Because of such long odds, we have focused on hard traces that have existed for thousands, millions, or even billions of years,” Dr. Dai said. .

“If the object has a liquid central core, a trapped primordial black hole could absorb the liquid core, whose density is higher than that of the outer solid layer,” Professor Stojković added.

“In that case, if the object was hit by an asteroid, the primordial black hole could escape from the object, leaving only a hollow shell.”

But would such a shell be strong enough to support itself, or would it simply collapse under its own tension?

Comparing the strength of natural materials such as granite and iron to their surface tension and surface density, the researchers found that such hollow objects could be less than one-tenth the radius of the Earth, making them smaller than normal We calculated that it was more likely to be an asteroid than a planet. .

“If it gets any bigger, it will collapse,” Professor Stojković said.

“These hollow objects could potentially be detected with telescopes. The mass, and therefore the density, can be determined by studying the objects' trajectories.”

“If an object's density is too low for its size, that's a good sign that it's hollow.”

For objects without a liquid core, the primordial black hole could simply pass through, leaving a straight microtunnel behind.

For example, a primordial black hole with mass 10^{twenty two} grams, leaving a tunnel 0.1 microns thick.

Large slabs of metal or other materials could serve as effective black hole detectors by monitoring the sudden appearance of these tunnels, but very old materials from buildings that are hundreds of years old Searching for existing tunnels has a higher probability. From the oldest to rocks that are billions of years old.

Still, even assuming that dark matter is indeed composed of primordial black holes, they calculated that the probability that a primordial black hole would pass through a billion-year-old rock is 0.000001.

“You have to compare costs and benefits. Does it cost a lot of money to do this? No, it doesn't,” Professor Stojković said.

“So, to say the least, it's unlikely that a primordial black hole will pass through you during your lifetime. Even if you did, you probably wouldn't notice.”

“Unlike rocks, human tissue has a small amount of tension, so the primordial black hole won't tear it apart.”

“And while the kinetic energy of a primordial black hole may be huge, it is moving so fast that it cannot release much of that energy during a collision.”

“If a projectile is moving through a medium faster than the speed of sound, the molecular structure of the medium has no time to react.”

“If you throw a rock through a window, it will probably break. If you shoot a window with a gun, it will probably just leave a hole.”

team's paper Published in a magazine physics of the dark universe.

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De Chan Dai and Dejan Stojković. 2024. We're looking for planets, asteroids, and tiny primordial black holes on Earth. physics of the dark universe 46: 101662;doi: 10.1016/j.dark.2024.101662