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The scientific world has been battling a serious issue for the past 50 years or so: the universe does not contain enough observable matter.
According to NASA, five times as much matter must exist in the universe for the observations made by scientists to make sense. The universe’s behavior cannot be explained by the matter we can see, which includes stars, planets, cosmic dust, and everything in between. Because it is invisible and does not interact with light, scientists refer to it as dark matter.
By observing stars orbiting on the edge of spiral galaxies, American astronomers Vera Rubin and W. Kent Ford were able to prove the existence of dark matter in the 1970s. They saw that these stars should have been flying apart, yet they were traveling too quickly for the observable matter and gravity of the galaxy to hold them together. The galaxy’s holding together by a substantial amount of invisible stuff was the only plausible explanation.
Rubin stated at the time that “what you see in a spiral galaxy is not what you get.” Her research expanded on a theory put forth by Swiss astronomer Fritz Zwicky in the 1930s and began the hunt for the elusive material.
Since then, researchers have attempted to directly examine dark matter and have even constructed sizable equipment to do so, but they have not been successful.
Renowned British physicist Stephen Hawking, whose primary research topic is black holes generated during the big bang, proposed early in the quest that dark matter might be concealed in these structures.
Researchers at the Massachusetts Institute of Technology have now resurrected the hypothesis, providing insight into the composition of these primordial black holes and maybe identifying a whole new class of unusual black holes in the process.
David Kaiser, one of the study’s authors, remarked, “It was really a wonderful surprise that way.”
“We were utilizing the well-known black hole calculations of Stephen Hawking, particularly his significant finding regarding the radiation that black holes release,” Kaiser stated. “These exotic black holes are a byproduct of explaining dark matter; they arise from attempts to address the dark matter problem.”
One quintillionth of a second, to start
Numerous theories have been proposed by scientists to explain dark matter, from extraterrestrial dimensions to unidentified particles. However, Hawking’s idea of black holes has only recently gained traction.
Until perhaps ten years ago, people didn’t really take it seriously, according to MIT graduate student and research coauthor Elba Alonso-Monsalve. “And that’s because, in the early 20th century, people thought black holes were just interesting mathematical facts and had no physical significance.”
As a result of the groundbreaking discovery in 2015 that Einstein’s gravitational waves are produced when black holes collide, we now know that almost every galaxy has a black hole at its heart.
According to Alonso-Monsalve, “the universe is actually teeming with black holes.” However, despite searches being conducted in all the expected locations, the dark matter particle has not been identified. This is not to argue that dark matter isn’t a particle or that black holes aren’t present in it. It might be both of them combined. However, black holes are now considered far more seriously as potential dark matter candidates.
Hawking’s theory has been validated by additional recent research, but Alonso-Monsalve and Kaiser’s work—which examines the precise formation process of primordial black holes—goes one step further and examines the work of MIT’s Germeshausen Professor of the History of Science and Physics Professor Kaiser .
These black holes must have formed in the first quintillionth of a second after the big bang, according to a study published in the journal Physical Review Letters on June 6. “That is really early, and a lot earlier than the moment when protons and neutrons , the particles everything is made of, were formed,” said Alonso-Monsalve.
She went on to say that protons and neutrons are elementary particles and cannot be found split apart in the real world. But since they are composed of even smaller particles called quarks that are bonded together by other particles called gluons, we know they are not.
Alonso-Monsalve continued, “It is too cold in the universe right now to detect quarks and gluons alone and unbound. However, during the hottest part of the big bang, they were able to survive on their own. Hence, unbound quarks and gluons were absorbed by the primordial black holes to produce them.
They would be essentially distinct from the astrophysical black holes that scientists typically see in the cosmos, which are formed when stars collapse, as a result of such a formation. Furthermore, a primordial black hole would be substantially smaller, with only an asteroid’s mass condensing into the volume of a single atom on average. However, they may explain all or most of the dark matter provided enough of these primordial black holes survived the early big bang and did not evaporate.
An enduring signature
The study suggests that another kind of black hole that has never been seen before must have developed as a kind of byproduct during the formation of the primordial black holes. These would have been even smaller, merely a rhino’s mass compressed into a volume smaller than that of a single proton.
Because of their tiny size, these tiny black holes would have been able to detect a unique and unusual characteristic known as a “color charge” from the quark-gluon soup in which they originated. According to Kaiser, this particular state of charge is unique to quarks and gluons and is never observed in common items.
They would be distinct from other black holes, which typically have no charge at all, due to their color charge. According to Alonso-Monsalve, “it is inevitable that these even smaller black holes would have formed as a byproduct (of the formation of primordial black holes), but they would not be around today, as they would have evaporated already.”
But when protons and neutrons were created, ten millionths of a second after the big bang, they might have still been around and could have changed the balance between the two particle kinds, leaving observable traces.
The delicate balance between the production of protons and neutrons depends on other elements that were present in the cosmos at the time. She continued, “If these color-charged black holes had survived, they might have slightly altered the proton-neutron balance (in favor of one over the other), enough for us to quantify it in the coming years.
According to Kaiser, the measurement may originate from sensitive equipment on orbiting satellites or telescopes on Earth. However, he noted that there might be an additional method to verify the presence of these unusual black holes.
“The process of creating a population of black holes is extremely violent and would cause massive reverberations across the surrounding space-time. Over cosmic history, those would weaken, but not to zero, according to Kaiser. “Small-mass black holes, an exotic state of matter that was an unexpected byproduct of the more commonplace black holes that could explain dark matter today, could be visible to the next generation of gravitational detectors.”
Various types of dark matter
What does this mean for the continuing dark matter detection studies, such as the South Dakota-based LZ Dark Matter Experiment?
According to Kaiser, “the hypothesis that there are exotic new particles remains an interesting hypothesis.” There are different types of huge experiments searching for complex techniques to detect gravitational waves, some of which are currently under construction. Indeed, they may potentially detect some of the anomalous signals resulting from the extremely intense process of primordial black hole development.
Alonso-Monsalve also mentioned the chance that primordial black holes only make up a small portion of dark matter. She remarked, “It doesn’t really have to be all the same.” Compared to conventional matter, which is composed of a wide variety of particles, dark matter is five times more prevalent. Why then should all dark matter objects be of the same kind?
The discovery of gravitational waves has brought primordial black holes back into the spotlight, but little is known about how they formed, according to Nico Cappelluti, an assistant professor in the University of Miami’s physics department. He was not part of the research team.
According to Cappelluti, “this work is an interesting, viable option for explaining the elusive dark matter.”
According to Yale University’s Joseph S. and Sophia S. Fruton Professor of Astronomy and Physics Priyamvada Natarajan, “The study is exciting and proposes a novel mechanism of formation for the first generation of black holes.” She did not participate in the study either.
If enough of these primordial black holes had existed up until that point, they would have affected the creation of all the hydrogen and helium that exists in our universe today, and those impacts might be observable, according to Natarajan.
“Apart from the fact that this suggests nature probably creates black holes starting from the earliest times through multiple pathways, what really excites me about this hypothesis is that it is one that can be tested through observations.”
read also: A recent investigation has confirmed the existence of dark matter.
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