MIT physicists link dark matter to “supercharged” microscopic black holes

During the first quintillionth of a second, the universe is estimated to have sprouted microscopic black holes with enormous amounts of nuclear charge. HAVE physicists.

MIT researchers suggest that primordial black holes, a possible form of dark matter, may have formed in the first moments after Big Bang and carried high levels of the nuclear property known as color charge. These supercharged black holes, despite their short existence, could have influenced the cosmology of the early universe and could explain some of the astronomical phenomena observed today.

Dark matter and primordial black holes

For every kilogram of matter we can see – from the phone in your hand to distant stars and galaxies – there are 5 kilograms of invisible matter that permeates our surroundings. This “dark matter” is a mysterious entity that eludes all forms of direct observation, yet makes its presence felt by an invisible pull on visible objects.

Fifty years ago, physicist Stephen Hawking proposed the idea of ​​what dark matter might be: a population of black holes that could have formed very soon after the big bang. Such “primordial” black holes would not be the goliaths we detect today, but rather microscopic regions of ultradense matter that would have formed in the first quintillionth of a second after the Big Bang and then collapsed and dispersed through space, trailing on. surrounding space-time in ways that could explain the dark matter we know today.

The discovery of supercharged black holes

Physicists at MIT have now discovered that this primordial process would also create some unexpected companions: even smaller black holes with an unprecedented amount of nuclear-physical properties known as “color charge.”

These smallest, “supercharged” black holes would be an entirely new state of matter that likely evaporated a fraction of a second after they were born. Yet they may have affected a key cosmological transition: the time when the first atomic nuclei were formed. Physicists hypothesize that color-charged black holes may have affected the balance of fusing nuclei in a way that astronomers may one day detect with future measurements. Such an observation would conclusively point to primordial black holes as the root of all dark matter today.

“Even though these short-lived exotic creatures are no longer in the world today, they could have influenced cosmic history in ways that might show up in subtle signals today,” says David Kaiser, Germeshausen Professor of the History of Science and Professor of Physics at MIT. “Within the idea that black holes are responsible for all dark matter, it gives us new things to look for.”

Kaiser and his co-author, MIT graduate student Elba Alonso-Monsalve, published their study June 6 in the journal Physical Review Letters.

Time before the stars

The black holes we know and detect today are the product of stellar collapse, when the center of a massive star collapses in on itself, creating a region so dense that it can bend space-time so that anything—even light—is trapped inside. . Such “astrophysical” black holes can be anywhere from a few times the mass of the Sun to many billions of times more massive.

“Primordial” black holes, on the other hand, can be much smaller and are thought to have formed before the stars. Before the universe even cooked up the basic elements, let alone stars, scientists believe that pockets of ultradense primordial matter could have accumulated and collapsed to form microscopic black holes that could have been so dense that they would have squeezed the mass of an asteroid into a region as small as a single atom. The gravitational pull of these small, invisible objects scattered throughout the universe could explain all the dark matter we don’t see today.

If so, what would these primordial black holes be made of? That’s the question Kaiser and Alonso-Monsalve tackled in their new study.

“People studied what distribution Black hole matter would have been in the early universe during this production, but it was never linked to what kinds of things would fall into these black holes at the time they were forming,” explains Kaiser.

Super charged rhinos

The MIT physicists first examined existing theories on the likely mass distribution of black holes when they first formed in the early universe.

“We realized that there is a direct connection between when the primordial black hole is formed and what kind of matter it is,” says Alonso-Monsalve. “And that time window is absurdly early.

She and Kaiser calculated that the primordial black holes must have formed within the first quintillionth of a second after the big bang. This flash of time would create “typical” microscopic black holes that were as massive as an asteroid and as small as an atom. It would also yield a small fraction of exponentially smaller black holes with the mass of a rhinoceros and a size much smaller than a single proton.

What would these primordial black holes be made of? To this end, they focused on studies investigating the composition of the early universe, and specifically on the theory of quantum chromodynamics (QCD) — the study of how quarks and gluons interact.

Quantum dynamics and the formation of black holes

Quarks and gluons are the basic building blocks of protons and neutrons – the elementary particles that combined to form the basic elements of the periodic table. Immediately after the Big Bang, physicists estimate, based on QCD, that the universe was extremely hot. plasma quarks and gluons, which then quickly cooled and combined to form protons and neutrons.

The researchers found that during the first quintillionth of a second, the universe would still be a soup of free quarks and gluons that had yet to come together. Any black holes that formed at this time would have absorbed unbound particles along with an exotic property known as “color charge”—a state of charge carried only by uncombined quarks and gluons.

The role of color charge in the dynamics of black holes

“Once we figured out 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 blob of matter that ends up in the primordial black hole?” says Alonso-Monsalve.

Using QCD theory, they worked out the color charge distribution that should exist in the hot early plasma. They then compared this to the size of the region that would collapse to form a black hole in the first quintillionth of a second. It turns out that most typical black holes wouldn’t have much colored charge at that time, because they would have formed by absorbing huge amounts of regions that had a mixture of charges, eventually creating a “neutral” charge.

Conclusion and future implications

But the smallest black holes would be full of color 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. While such “extreme” black holes have been hypothesized for decades, no one has yet discovered a realistic process by which such oddities could actually form in our universe.

Professor Bernard Carr of Queen Mary University of London, an expert on primordial black holes who first worked on the subject with Stephen Hawking, describes the new work as “exciting”. Carr, who was not involved in the study, says the work “shows that there are circumstances under which a small fraction of the early universe can get into objects with enormous amounts of color charge (at least for a while), exponentially greater than what has been identified in previous studies QCD.”

Supercharged black holes would evaporate quickly, but perhaps only after the first atomic nuclei had begun to form. Scientists estimate that this process began about one second after the Big Bang, which would have given the extreme black holes enough time to disrupt the equilibrium conditions that would have prevailed when the first nuclei began to form. Such perturbations could potentially affect how these earliest nuclei formed, in ways that could one day be observed.

“These objects could have left some exciting observational imprints,” Alonso-Monsalve muses. “They could change the balance of this and that, and that’s the kind of thing you start to wonder about.”

Reference: “Primordial Black Holes with QCD Color Charge” by Elba Alonso-Monsalve and David I. Kaiser, 6 Jun 2024, Physical Review Letters.
DOI: 10.1103/PhysRevLett.132.231402

This research was supported in part by the US Department of Energy. Alonso-Monsalve is also supported by a fellowship from the MIT Department of Physics.