The tiny primordial black holes formed in the first fraction of a second after the Big Bang could have had company in the form of even smaller “supercharged” black holes with the mass of a rhinoceros that rapidly evaporated.
A team of researchers came up with the theory that these small “rhino” black holes, which would represent an entirely new state of matter, would be filled to the brim with “colored charge.” This is a property of fundamental particles called quarks and gluons that is related to their strong force interactions with each other and is not related to “color” in the everyday sense.
These supercharged black holes would have been created with primordial black holes when microscopic regions of ultradense matter collapsed in the first quintillionth of a second after the Big Bang.
Although these newly theorized black holes would evaporate just a fraction of a second after they were born, they could affect a key cosmological transition: the forging of the first atomic nuclei. This means they may have left a signature that is recognizable today.
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The research team believes that supercolor-charged black holes may have affected the balance of fusing nuclei in the baby universe. Although exotic objects ceased to exist in the earliest moments of the cosmos, future astronomers could potentially still detect this influence.
“Although these short-lived exotic creatures don’t exist today, they could have influenced cosmic history in ways that might show up in subtle signals today,” study co-author David Kaiser, a professor of physics at the Massachusetts Institute of Technology. (MIT), said in a statement.
“Within the idea that black holes are responsible for all dark matter, it gives us new things to look for,” he added, referring to the mysterious substance that makes up about 85% of the material universe.
Not all black holes are created equal
When we think of a black hole, the immediate image that may come to mind is cosmic titan-like supermassive black holes with a mass of millions or even billions of times that of the Sun. These black holes lie at the heart of galaxies, dominate their surroundings, and are created by a chain of mergers of successively larger pairs of black holes.
More common in the universe are stellar-mass black holes tens or hundreds of times that of the Sun, which are born when massive stars run out of fuel for nuclear fusion and collapse.
These two types of black holes, as well as the elusive intermediate black holes between these two mass ranges, are classified as “astrophysical black holes”. Scientists have long assumed that non-astrophysical black holes with masses between Earth and a large asteroid may have been born sometime after the Big Bang.
Rather than being formed by a collapsing star, these primordial black holes may have formed from much smaller regions of collapsing matter before the first stars or even the simplest atoms ever appeared.
The more massive a black hole is, the wider its outer boundary, or “event horizon.” If the primordial black hole had a mass around Earth, it would be no wider than a dime. If it had the mass of a large asteroid, it would be smaller than an atom.
The reason we use the past tense when describing these black holes is that current theories suggest that these primordial black holes would have been so small that they rapidly lost mass through the “escape” of a type of thermal radiation called Hawking radiation. This would lead to their vaporization, meaning they would not be in space today.
Some scientists have proposed “rescue mechanisms” that could allow primordial black holes to survive into the modern epoch of the cosmos. If these mechanisms are valid, then primordial black holes could indeed be responsible for dark matter.
Dark matter is so mysterious because, although it makes up about 85% of the matter in the universe, it does not interact with light, and therefore cannot be the same as the remaining 15% of “stuff” in the universe, which includes stars. planets, moons, our bodies and the cat next door.
Primordial black holes could be suitable for dark matter because, like all black holes, they would have bounded event horizons. These are light-trapping surfaces, which also mean that black holes, like dark matter, neither emit nor reflect light.
To better investigate the connection between dark matter and primordial black holes, Kaiser and MIT graduate student Elba Alonso-Monsalve set out to find out what these small and early black holes are (or were) made of.
“People have studied what the mass distribution of black holes would have been during this production in the early universe, but they’ve never linked it to what kinds of things would have fallen into these black holes at the time they were forming,” Kaiser explained.
Supercharged rhinos were the original companions of black holes
The first step for both researchers was to look at existing theories of primordial black holes and how their mass would have been distributed during the formation of the universe.
“Our finding was that there is a direct correlation between when the primordial black hole forms and what mass it forms from,” explained Alonso-Monsalve. “And that time window is absurdly early.
In this case, “absurdly early” means within a quintillionth of a second after the big bang. In this short period, “standard” primordial black holes with masses around large asteroids and widths less than an atom would be born.
Yet Alonso-Monsalve and Kaiser predict that this brief spell would also see the birth of a small fraction of exponentially smaller black holes with masses around the rhinoceros and sizes much smaller than a single proton, the particles that (along with neutrons) form the nuclei at the heart of atoms.
Both of these sizes of black holes in the early universe would have been surrounded by a dense sea of ​​quarks and gluons. These elementary particles are not found freely in the universe during its current era, they are bound in particles such as protons and neutrons. However, in the dense early universe there was a “hot soup” or plasma of free quarks and gluons that had yet to coalesce.
Not only would all the black holes created in the early universe feed on this plasma soup, but they would also absorb a property of free unbound quarks and gluons called color charge.
“Once we found that these black holes form in a quark-gluon plasma, the most important thing we had to figure out was how much color charge is contained in the droplet of matter that ends up in the primordial black hole?” Alonso-Monsalve said.
Using a theory called “quantum chromodynamics” that describes the action of the strong force between quarks and gluons, the pair calculated the distribution of color charge that should have existed in the hot, dense plasma of the early universe. They then compared this distribution to the size of the region that would be able to collapse and give birth to a black hole in just the first quintillionth of a second of the universe.
This revealed that a “typical” primordial black hole would not absorb large amounts of color charge. This is because the larger area of ​​quark-gluon plasma they consumed would contain a mixture of colored charges that would add to the neutral charge.
The pair found that rhinoceros-mass black holes formed from a smaller fraction of quark-gluon plasma would, however, be full of colored charge. In fact, they would contain the maximum amount of any type of charge allowed for a black hole, according to the basic laws of physics.
It’s not the first time such “extreme” black holes have been hypothesized, but Alonso-Monsalve and Kaiser are the first scientists to propose a realistic process by which such cosmic oddities could actually form in our universe.
Although supercharged black holes would evaporate quickly, they could still be around one second after the big bang, when the first atomic nuclei began to form. This means that rhino black holes would have enough time to throw the conditions in the universe out of balance. These perturbations could have affected matter in ways that can still be observed today.
“These objects could have left some exciting observational imprints,” Alonso-Monsalve concluded. “They could change the balance of this and that, and that’s the thing you can start to wonder about.”
The team’s research was published Thursday (June 6) in the journal Physical Review Letters.