Even small primordial black holes formed during the first fraction of a second after the Big Bang rapidly evaporated with the mass of the rhinoceros in the form of small „supercharged” black holes.
The team of researchers hypothesized that these tiny „rhino” black holes would be filled to the brim with „color charge,” indicating a state of completely new matter. This is a property of fundamental particles called quarks and gluons, which are associated with strong force interactions with each other, and is not associated with „color” in the everyday sense.
These supercharged black holes were created along with primordial black holes when microscopic regions of ultradense matter collapsed in the first quintillionth of a second following the Big Bang.
Although the newly theorized black holes evaporate only a fraction of a second after their formation, they may have affected a key cosmological change: the creation of the first nucleus. That means they may have left a signature that is detectable today.
Related: If the Big Bang created smaller black holes, where were they?
The research team hypothesizes that super-color-charged black holes may have affected the balance of merging nuclei in the baby universe. Even if the first moments of the universe were devoid of exotic objects, future astronomers will be able to detect this influence.
„Even though these short-lived, exotic creatures no longer exist today, they may have influenced cosmic history in ways that can show up in subtle signals today,” said study co-author David Kaiser, a professor of physics at the Massachusetts Institute of Technology. (MIT), said in a statement.
„The idea that all dark matter can be accounted for by black holes gives us new things to look for,” he added, referring to the mysterious matter that makes up 85% of the universe.
Not all black holes are created equal
When picturing a black hole, the immediate image that comes to mind is supermassive black holes like the cosmic Titan. These black holes sit at the center of galaxies, dominate their surroundings, and are formed 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, that give birth to massive stars when they run out of fuel for nuclear fusion and collapse.
These two types of black holes and the elusive intermediate black holes between these two mass ranges are classified as „astronomical black holes”. Scientists have long hypothesized that non-astrophysical black holes with masses between Earth and a massive asteroid’s black hole may have been born sometime after the Big Bang.
Rather than forming from the collapse of a star, these primordial black holes may have formed from very small patches of collapsing material before the first stars or even simple atoms emerged.
The more massive the black hole, the wider its outer boundary or „event horizon.” If there was a primordial black hole around the Earth, it would have been no wider than a dime. If it had a large asteroid mass, 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 a „leakage” of thermal radiation called Hawking radiation. This would have led to their evaporation, meaning they would no longer exist in the universe today.
Some scientists have proposed „recovery mechanisms” that would allow primordial black holes to persist into the modern era of the universe. If these mechanisms are valid, then primordial black holes may indeed be responsible for dark matter.
Dark matter is so mysterious because, despite representing 85% of the matter in the universe, it does not interact with light and thus cannot be like the other 15% of „matter” in the universe, which includes stars. Planets, moons, our bodies and the cat next door.
Primordial black holes are a good match for dark matter because, like all black holes, they are bounded by event boundaries. These are light-trapping surfaces, like black holes and black matter, that neither emit nor reflect light.
To better investigate the dark matter/primordial black hole connection, Kaiser and MIT graduate student Elba Alonso-Mansalve set out to find out what made (or are) these tiny and early black holes.
„People have studied what the distribution of black hole masses might have been during this early cosmic production, but never incorporated what kind of material would have fallen into those black holes at the time of their formation,” Kaiser explained.
The primordial black hole companions are supercharged rhinoceroses
The first step for the two researchers is to look at existing theories of primordial black holes and how their mass was distributed as the universe formed.
„Our realization is that there is a direct correlation between when a primordial black hole forms and with what mass it forms,” explained Alonso-Mansalve. „That window of time is ridiculously early.”
In this case, the „absurd beginning” is within a billionth of a second following the Big Bang. During this brief period, „standard” primordial black holes with masses and subatomic widths would have formed around large asteroids.
Nevertheless, Alonso-Monsalve and Kaiser predicted that this brief spell would have seen the birth of a tiny black hole, the mass around the rhinoceros and particles with sizes much smaller than a proton (along with neutrons ) that form the nuclei at the heart of atoms.
In the early universe these two-sized black holes were surrounded by a dense sea of quarks and gluons. These elementary particles are not found free in the universe in its present epoch, but are bound into particles such as protons and neutrons. However, in the dense early universe, a „hot soup” or plasma of free quarks and gluons had not yet coalesced.
Black holes forming in the early universe not only feed on this plasma soup, but also absorb the properties of free quarks and gluons, known as color charge.
„Once we find that these black holes form in a quark-gluon plasma, the most important thing we need to figure out is how much color charge is in the bubble of matter that ends up in a primordial black hole?” Alonso-Monsalve said.
Turning to a theory called „quantum chromodynamics,” which describes the operation of the strong force between quarks and gluons, the two calculated the distribution of colored current that must have existed throughout the hot, dense plasma of the early universe. They then compared this distribution to the size of a particle that would be born from a collapsing black hole in the first quintillionth of a second in the universe.
This revealed that a „typical” primordial black hole would not have absorbed large amounts of color charge. That’s because a large fraction of the quark-gluon plasma they’ve ingested contains a mixture of color charges that add to the neutral charge.
However, rhinoceros-mass black holes, formed from tiny mergers of quark-gluon plasma, are packed with colored charge, the two found. In fact, they contain the maximum amount of charge of any kind allowed for a black hole, according to the basic laws of physics.
This is not the first time that such „super” black holes have been hypothesized, but Alonso-Mansalve and Kaiser are the first scientists to lay out a realistic process by which cosmic freaks could actually form in our universe.
Although rhinoceros-supercharged black holes evaporate quickly, they may have existed for about a second after the Big Bang when the first nuclei began to form. This means that rhinoceros black holes would have had plenty of time to throw conditions in the universe out of balance. Those disturbances may have affected the subject in ways that are still noticeable today.
„These objects may have left some amazing observational imprints,” Alonso-Monsalve concluded. „They may have tipped the balance against this, and that’s the thing one starts to wonder.”
The team’s research was published Thursday (June 6) in the journal Physical review letters.