The tiny primordial black holes created during the first fraction of a second after the Big Bang may 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 has theorized that these tiny “rhinoceros” black holes, which would represent an entirely new state of matter, would be filled to the brim with “color charge.” This is a property of fundamental particles called quarks and gluons that is related to their strong strong 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 have evaporated only a fraction of a second after they were created, they may have influenced 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 thinks that super-charged black holes may have affected the balance of merger nuclei in the infant universe. Although exotic objects ceased to exist in the first moments of the cosmos, future astronomers could potentially still detect this influence.
“Although these short-lived exotic creatures are not around today, they may have influenced cosmic history in ways that can 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 all dark matter can be accounted for by black holes, 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 picture a black hole, the immediate image that may come to mind is cosmic supermassive black holes like titanium, with masses millions or even billions of times that of the sun. These black holes sit at the heart of galaxies, dominating their surroundings, and are created by a chain of mergers of progressively larger pairs of black holes.
Most common in the universe are stellar-mass black holes tens or hundreds of times the mass 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 hypothesized that there may once have been non-astrophysical black holes born shortly after the Big Bang, with masses between those of Earth and that of a large asteroid.
Rather than forming from the collapse of a star, these primitive black holes could have formed from much smaller pieces of matter collapsing before the first stars or even the simplest atoms emerged.
The more massive a black hole, the wider its outer boundary or “event horizon”. If a primordial black hole had a mass about that of Earth, it would have been no wider than a dime. If it had the mass of a large asteroid, it would have been smaller than an atom.
The reason we use past tense when describing these black holes is because current theories suggest that these primordial black holes would have been so small that they rapidly lost mass through the “leakage” of a type of thermal radiation called Hawking radiation . This would have resulted in their evaporation, meaning they would not be around in the universe today.
Some scientists have proposed “rescue mechanisms” that could allow primordial black holes to persist into the modern age of the cosmos. If these mechanisms are valid, then primordial black holes may actually constitute dark matter.
Dark matter is so mysterious because, despite representing about 85% of the matter in the universe, it does not interact with light and thus cannot be the same as the other 15% of “stuff” in the cosmos that includes stars. the planets, the moons, our bodies and the cat next door.
Primordial black holes may be a good fit for dark matter because, like all black holes, they will be bounded by event horizons. These are light-catching surfaces which also mean that black holes, like dark matter, do not emit or reflect light.
To better explore the dark matter/primordial black hole connection, Kaiser and MIT graduate student Elba Alonso-Monsalve set out to find out where these tiny, early black holes are (or were).
“People have studied what the mass distribution of black holes would have been like during this early production of the universe, but they never related it to what kind of stuff would have fallen into those black holes at the time they were forming. formed,” Kaiser explained.
The primordial companions of the black hole were supercharged rhinos
The first step for the two researchers was to look at pre-existing theories of primordial black holes and how their mass would have been distributed during the formation of the universe.
“Our understanding was that there is a direct relationship between when a primordial black hole forms and at what mass it forms,” explained Alonso-Monsalve. “And this time window is absurdly early.”
In this case, “absurdly early” means within a quintillionth of a second after the Big Bang. This short period would have seen the birth of “standard” primordial black holes with masses around that of large asteroids and widths of less than an atom.
However Alonso-Monsalve and Kaiser predict that this brief spell would also have seen the birth of a small fraction of exponentially smaller black holes, with masses around that of a rhinoceros and sizes much smaller than a proton. only, the particles that (along with neutrons) make up 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 epoch, binding into 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 combine.
Not only would any black holes formed in the early universe feed on this plasma soup, but they would also absorb a property of unbound free quarks and gluons called color charge.
“Once we realized that these black holes form in a quark-gluon plasma, the most important thing we had to figure out was, how much color charge does the blob of matter contain that will end up in a primordial black hole?” Alonso-Monsalve said.
Turning to a theory called “quantum chromodynamics,” which describes the action of the strong force between quarks and gluons, the pair calculated the distribution of colored charge that must have existed throughout the hot, dense plasma of the early universe. . They then compared this distribution to the size of a region that would be able to collapse and give birth to a black hole in just the first quintillionth of a second of the cosmos.
This revealed that the “typical” primordial black hole would not have absorbed a large amount of color charge. This is because the larger region of quark-gluon plasma they consumed would contain a mixture of color charges, adding up to a neutral charge.
Rhino mass black holes that form from a smaller fraction of quark-gluon plasma, however, would be packed with color charge, the pair found. In fact, they would have contained the maximum amount of any kind of charge allowed for a black hole, according to the basic laws of physics.
This is not the first time such “extreme” black holes have been hypothesized, but Alonso-Monsalve and Kaiser are the first scientists to posit a realistic process by which such cosmic wonders could actually have formed in the universe. ours.
Although supercharged rhinoceros black holes would have evaporated quickly, they may still have been around a second after the Big Bang when the first atomic nuclei began to form. This means that rhinoceros black holes would have plenty of time to throw conditions in the cosmos out of balance. These disturbances may have affected matter in a way that can still be observed today.
“These objects may have left some exciting observational traces,” Alonso-Monsalve concluded. “They could have changed the balance of this versus that, and that’s the kind of thing you start to wonder about.”
The team’s research was published Thursday (June 6) in the journal Physical Review Letters.
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