Dark matter: How primordial black holes could explain a long-standing mystery

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For nearly 50 years, the scientific community has struggled with a significant problem: there is simply not enough visible matter in the universe.

All the stuff we can see—stars, planets, cosmic dust, and everything in between—can’t account for why the universe works, and researchers have to be five times more likely to make observations. According to NASA. Scientists call it dark matter because it does not interact with light and is invisible.

In the 1970s, American astronomers Vera Rubin and W. Kent Ford confirmed the existence of dark matter by looking at stars orbiting the edge of spiral galaxies. They noted that these stars were moving too fast to be held together by the galaxy’s visible matter and its gravity—instead they must have flown apart. The only explanation is a large amount of invisible matter that holds the galaxy together.

“What You See in the Swirl Galaxy” Rubin said At that point, “It’s not what you get.” His work built on a hypothesis developed by Swiss astronomer Fritz Zwicky in the 1930s and launched the search for the elusive object.

Since then, scientists have been trying to direct and even construct dark matter Large appliances Find it – but so far, no luck.

At the beginning of the search, the famous British physicist Stephen Hawking suggested that dark matter could be hidden in black holes – the main subject of his work – formed during the Big Bang.

Bettman Archive/Getty Images

The late physicist Stephen Hawking hypothesized that dark matter could be hidden in black holes formed during the Big Bang.

Now, a new study by researchers at the Massachusetts Institute of Technology has brought the theory back into focus, revealing what made these primordial black holes and potentially discovering an entirely new type of exotic black hole in the process.

“It was really a wonderful surprise,” said David Kaiser, one of the study’s authors.

“We use Stephen Hawking’s famous calculations about black holes, particularly his important conclusion about the radiation emitted by black holes,” Kaiser said. “These exotic black holes emerge from trying to solve the dark matter problem—they’re a byproduct of explaining dark matter.”

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Scientists have made many guesses as to what dark matter might be, from unknown particles to extra dimensions. But Hawking’s theory of black holes has come into play recently.

“People didn’t take it seriously until 10 years ago,” said study co-author Elba Alonso-Monsalve, an MIT graduate student. Thought, nothing physical.”

We now know that almost every galaxy has a black hole at its center, a discovery by Einstein’s researchers. Gravitational waves A major discovery made by colliding black holes in 2015 made it clear that they are everywhere.

“In fact, the universe is full of black holes,” Alonso-Mansalve said. “But despite looking everywhere people expect to find it, the dark matter particle hasn’t been found. We can’t say that dark matter is not a particle, or that it’s definitely black holes. It could be a combination of the two. But now, black holes are being taken very seriously as candidates for dark matter.

Others Recent studies have confirmed the validity of Hawking’s hypothesis, but the work of Alonso-Mansalve and Kaiser, professor of physics and the Germeshausen Professor of the History of Science at MIT, goes a step further and examines what happened when primordial black holes first formed. .

The studyPublished June 6 in the journal Physical Review Letters, it reveals that these black holes must have appeared in the first quintillionth of a second after the Big Bang: “It’s really early, and much earlier than the moment when protons and neutrons exist. The particles are all created, created,” Alonso-Monsalve said.

In our everyday world, protons and neutrons cannot be detected broken down and behave as elementary particles. However, we know they don’t exist because they are made up of tiny particles called quarks, held together by other particles called gluons.

“You can’t find quarks and gluons alone and free in the universe right now because it’s so cold,” Alonso-Monsalve added. “But at the beginning of the Big Bang, when it was really hot, they were seen as single and independent. So primordial black holes are formed by absorbing free quarks and gluons.

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Such a formation would make it fundamentally different from the astrophysical black holes that scientists typically observe in the universe, which are the result of collapsing stars. Also, a primordial black hole is very small – only the mass of an asteroid is condensed, on average, into the volume of an atom. But if a sufficient number of these primordial black holes have survived to the present without evaporating in the initial Big Bang, they could account for all or most of the dark matter.

During the formation of primordial black holes, another type of previously unseen black hole must have formed as a byproduct, according to the study. These would have been even smaller – the mass of a RhinocerosLess than one proton is condensed.

These tiny black holes, because of their tiny size, can pick up a rare and exotic property from the quark-gluon soup they are created from, called “color charge”. It’s a charge state unique to quarks and gluons, not found in ordinary matter, Kaiser said.

This color charge makes them unique among black holes, which normally have no charge. “It’s inevitable that even these tiny black holes formed as a byproduct[of the formation of primordial black holes],” Alonso-Mansalve said, “but they wouldn’t exist today because they’ve already evaporated.”

However, if they had been around for ten millionths of a second in the Big Bang, they could have left observable signatures by changing the balance between the two types of particles as protons and neutrons were formed.

“The balance of how many protons and how many neutrons are created is very delicate, and depends on what other matter was in the universe at the time. If these black holes with colored charge still existed, they could have shifted the balance between protons and neutrons (in favor of one or the other), and in the next few years, we It can be measured,” he added.

The measurement could come from Earth-based telescopes or sensors on orbiting satellites, Kaiser said. But he said there might be another way to confirm the existence of these exotic black holes.

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“The creation of a population of black holes is a very violent process that sends enormous ripples through the surrounding space-time. They are focused on cosmic history, but not to zero,” Kaiser said. is an unexpected byproduct of very ordinary black holes.”

What this means for current experiments trying to detect dark matter LZ Dark Matter Experiment In South Dakota?

“The idea that there are attractive new particles is an interesting hypothesis,” Kaiser said. “There are other kinds of big experiments, some of which are under construction, looking for fancy ways to detect gravitational waves. And they might actually pick up some spurious signals from the very violent creation process of primordial black holes.

Alonso-Monsalve added that primordial black holes are part of dark matter. “It doesn’t really have to be the same,” he said. “There is five times more dark matter than regular matter, and regular matter is made up of a whole bunch of different particles. So why does dark matter have to be the same type of matter?

According to Nico Cappelluti, an assistant professor in the Department of Physics at the University of Miami, primordial black holes have regained popularity with the discovery of gravitational waves. He is not interested in studies.

“This work is an interesting, viable option to explain the elusive dark matter,” Cappelluti said.

The study is exciting and proposes a new mechanism for creating the first generation of black holes, said Yale University’s Joseph S. and Sophia S. said Priyamvatha Natarajan, Fruton Professor of Astronomy and Physics. She is also not interested in studies.

“All the hydrogen and helium in our universe today was created in the first three minutes, and if these primordial black holes were big enough, they would have affected that process, and those effects would have been detectable,” Natarajan said. .

“I find it very exciting that this is an observationally testable hypothesis, suggesting that nature can create black holes from very early times through multiple pathways.”

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