{"id":1966,"date":"2025-08-24T16:20:03","date_gmt":"2025-08-24T13:20:03","guid":{"rendered":"https:\/\/planeta21vek.ru\/eng\/?p=1966"},"modified":"2025-11-20T12:37:34","modified_gmt":"2025-11-20T09:37:34","slug":"two-theories-about-the-relationship-between-dark-matter-and-black-holes","status":"publish","type":"post","link":"https:\/\/planeta21vek.ru\/eng\/2025\/08\/24\/two-theories-about-the-relationship-between-dark-matter-and-black-holes\/","title":{"rendered":"Two Theories About the Relationship Between Dark Matter and Black Holes"},"content":{"rendered":"

Tiny black holes that formed seconds after the birth of the universe may be around longer than expected, leading researchers to believe that primordial black holes could be the source of dark matter, the most mysterious substance in the universe.<\/span><\/p>\n

<\/p>\n

Dark matter is currently one of the most pressing problems in physics. This is because, despite making up about 85% of the matter in space, it remains virtually invisible to our eyes because it does not interact with light. The study was published in 2024 on Space.com.<\/span><\/p>\n

Because the particles that make up the atoms that make up the \u201ceveryday\u201d objects we see, like stars, planets, and our own bodies, clearly interact with light, this has prompted a search for dark matter particles beyond the Standard Model of particle physics. Many scientists believe that the answer may still lie within the Standard Model, if we consider cosmic objects that we typically think of as incredibly massive and even monstrous: black holes.<\/span><\/p>\n

Valentin Toss and Ana Alexander of the Max Planck Institute suggest that tiny black holes formed more than 13.8 billion years ago, just after the Big Bang, no larger than a proton, could form clumps that could be potential sources of dark matter, without the need to discover new physics.<\/span><\/p>\n

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\nIllustration of a dark matter cloud. Could it actually be a black hole cluster? X-ray: NASA\/CXC\/CfA\/M.Markevich et al.; Optical: NASA\/STScI; Magellan\/University of Arizona\/D.Clow et al.; Lensing map: NASA\/STScI; ESO WFI; Magellan\/University of Arizona\/D.Clow et al.<\/span><\/em><\/p>\n

The recent change in thinking about how black holes “evaporate” has not only led to a re-evaluation of the possibility of primordial black holes as sources of dark matter, but also, since searches for dark matter particles remain largely unsuccessful, more researchers might begin to take the primordial black hole theory as a source of dark matter more seriously.<\/span><\/p>\n

“As the name suggests, ‘primordial black holes’ are a type of black hole that form early in the universe,” Toss told Space.com. “Basically, within the first fraction of a second of the universe’s existence.”<\/span><\/p>\n

He explained that all the structures we see in the universe, from superclusters of galaxies to galaxies themselves, formed from small pockets of increased density in space that were present in the early universe. If the early universe experienced much larger density fluctuations than those that created these structures, and these fluctuations collapsed before galaxies formed, these pockets of increased density could have provided the basis for the formation of primordial black holes.<\/span><\/p>\n

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\nAnatomy of a black hole. Regardless of size, all black holes have event horizons. ESO<\/span><\/em><\/p>\n

Toss added that, depending on the timing and scale of the collapse, these primordial black holes could have very different masses. The primordial black holes that Toss and Alexander considered possible candidates for dark matter would have masses ranging from a few tons to a thousand tons, less than the mass of a planet and more consistent with the mass of a small asteroid.<\/span><\/p>\n

Considering that the smallest black holes discovered by scientists to date, known as stellar-mass black holes, have masses equivalent to between 3 and 50 solar masses, which itself is 2.2 times 1027 (22 followed by 26 zeros) tons, these primordial black holes are incredibly small.<\/span><\/p>\n

Like their larger counterparts \u2014 black holes formed either by the collapse of massive stars or by the merger of relatively smaller black holes \u2014 primordial black holes would have a light-stopping outer boundary called an event horizon, Alexander said. The diameter of this horizon is determined by the mass of the black hole, meaning the event horizon would be incredibly small in such cases. \u201cSmaller than the radius of a proton,\u201d Alexander said.<\/span><\/p>\n

Previously, small primordial black holes were ruled out as dark matter candidates because all black holes were thought to “leak” a special type of thermal radiation, first proposed by Stephen Hawking in 1974 and later named “Hawking radiation.”<\/span><\/p>\n

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\nA diagram showing the expansion history of the universe. Primordial black holes may have formed due to density fluctuations before the first stars formed. NASA\/WMAP Science Team\/Image by Dana Berry<\/span><\/em><\/p>\n

The smaller a black hole is, the faster it should emit Hawking radiation, and therefore the faster it should evaporate. This means that if primordial black holes ever existed, the smallest examples should not exist today, although dark matter obviously does.<\/span><\/p>\n

“Primordial black holes with the masses that Ana and I are looking at now were previously essentially ruled out because they were assumed to have completely evaporated into the universe by this point,” Toss said.<\/span><\/p>\n

However, recent work by Georgi Dvali, a theoretical physicist at the University of Munich who collaborated with Thoss and Alexander, has shown that the evaporation process stops at a certain point, meaning that primordial black holes with the masses the scientists were considering could reach a semi-stable state.<\/span><\/p>\n\n

\u201cIn order to reduce its mass through Hawking radiation, a black hole has to \u2018rewrite\u2019 its information or something else. This rewriting process takes time,\u201d Alexander explained. \u201cIt\u2019s called the \u2018memory burden\u2019 because that memory now has to be transferred to something else, and it just slows down the overall evaporation process. So it\u2019s a kind of stabilization.\u201d<\/span><\/p>\n

This “escape mechanism” means that primordial black holes once again become potential candidates for dark matter.<\/span><\/p>\n

However, the fact that primordial black holes may exist in the universe today does not mean that they should be considered the source of dark matter. However, there are other reasons to link these tiny hypothetical black holes to the mysterious matter that makes up the universe.<\/span><\/p>\n

Perhaps the most obvious connection is the lack of interaction between dark matter and light. Dark matter neither emits nor reflects light, and the event horizon that encloses all black holes is the point at which the escape velocity required to cross it exceeds the speed of light. This means that primordial black holes would \u201ccapture\u201d all incoming light, leading to the apparent lack of interaction.<\/span><\/p>\n

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\nIllustration showing a cluster of tiny primordial black holes that may be the source of dark matter. Robert Lee<\/span><\/em><\/p>\n

\u201cIf primordial black holes are light enough, somewhere around planetary mass, they behave like dark matter particles in all the ways we care about,\u201d Toss said. \u201cIn standard models, dark matter is \u2018collisionless,\u2019 so dark matter particles don\u2019t interact with each other enough to affect the universe.\u201d<\/span><\/p>\n

He added that if primordial black holes were lighter than planetary masses, then even on cosmic time scales they would be so small that collisions would be extremely rare. These primordial black holes would likely cluster together, creating the gravitational effects we now attribute to dark matter, such as exerting a gravitational pull on rapidly rotating galaxies to keep them from flying apart.<\/span><\/p>\n

But if primordial black holes must cluster together to explain the effects of dark matter, what’s to stop them from getting closer and merging to form larger black holes? Wouldn’t a cluster of tiny black holes eventually turn into one huge black hole? Thoss said this question has been explored, and the answer is simple: “No.”<\/span><\/p>\n

“Even if you take clustering into account, the time scales of the mergers are so large that over the entire history of the Universe they could only have merged into truly massive black holes,” he continued.<\/span><\/p>\n

Toss added that the beauty of using primordial black holes as an explanation for dark matter is that, unlike invoking a hypothetical particle like the axion to explain the mystery, primordial black holes do not require an extension of the Standard Model of particle physics – the best explanation we have for the universe at subatomic scales.<\/span><\/p>\n

However, it will be incredibly difficult to confirm that primordial black holes are dark matter, if they do explain the phenomenon. Again, their ability to trap light means they are effectively invisible. Also, at such small sizes, they do not exert the same powerful gravitational pull as their stellar and supermassive cousins.<\/span><\/p>\n

Even so, if a cluster of primordial black holes is discovered, there will be no real way to distinguish between many small black holes and one large black hole.<\/span><\/p>\n

Despite this difficulty, Toss and Alexander intend to continue to study primordial black holes\u2014at least in theory. If dark matter candidate particles continue to elude detection, perhaps the solution lies in getting more physicists to analyze the metaphorical boundary between particle physics and cosmology.<\/span><\/p>\n

“I wouldn’t say that primordial black holes have ever been dismissed as dark matter candidates; although they were ignored for a while,” Alexander said. “Now, given that we don’t have any data on dark matter particles, I think it’s becoming more and more relevant to consider this option.”<\/span><\/p>\n

The next theory: dark matter, the most mysterious “stuff” in the universe, could be a kind of cosmic middleman, allowing supermassive black holes to get past the final hurdle before colliding and merging into one.<\/span><\/strong><\/span><\/p>\n

Astronomers have long understood that when galaxies collide to form larger, misshapen galaxies, the supermassive black holes at their centers are also pulled toward each other. Eventually, these black holes merge, too, producing an even more monstrous supermassive black hole and a shrill scream through the fabric of space and time called gravitational waves. Alonso-Alvarez and his team\u2019s findings are discussed in a paper published July 9, 2025, in the journal Physical Review Letters.<\/span><\/p>\n

While the detection of gravitational waves has provided us with evidence of this collision process and has been truly fundamental to our understanding of how supermassive black holes acquire masses equivalent to millions or even billions of suns, there is an unsolved problem.<\/span><\/p>\n

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\nThe diagram shows the three main stages of black hole mergers, with stage 2 being the theoretical phase that explains the final parsec problem. Robert Lee. Space.com<\/span><\/em><\/p>\n

Astrophysicists have good models of the late stages of supermassive black hole mergers, but scientists still don’t fully understand how these cosmic giants manage to travel the last 3.3 light years (also known as a “parsec”) between them to initiate the merger process. This problem has been dubbed the “last parsec problem.”<\/span><\/p>\n

Dark matter could help supermassive black holes begin the merger process, but this theory only works if the dark matter particles interact with each other.<\/span><\/p>\n

The process of supermassive black hole mergers is complicated because it relies on the black holes finding each other, forming a binary system, and then the orbital distance between them slowly shrinking. When the distance between the two black holes was about a parsec, scientists were worried because, according to existing calculations, the merger seemed to stall.<\/span><\/p>\n

This is a discovery based on mathematical modeling and on the interaction of dark matter with itself. More specifically, in order to mediate between black holes, dark matter particles must disperse upon collision.<\/span><\/p>\n

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\nA pie chart showing how much dark matter outnumbers the “normal” matter in the universe that makes up everything we see. Robert Lee. Space.com<\/span><\/em><\/p>\n

For this reason, following this theory could not only solve the final parsec problem, but also perhaps finally figure out what dark matter is made of, thereby solving one of the most fundamental mysteries in science.<\/span><\/p>\n

Dark matter may not only consist of particles that don’t fit our best models of the subatomic world, but may also be vastly more massive than particles of “everyday” matter.<\/span><\/p>\n\n

Dark matter particles “outnumber” normal particles by between 5 to 1 and 6 to 1. This means that all the “stuff” you see around you makes up only 15% of the mass of the cosmos.<\/span><\/p>\n

We know dark matter exists because, despite not interacting with light or normal matter, dark matter interacts with gravity. When it does, the effects it causes can affect the behavior of normal matter and light. For example, researchers have found that without the gravitational influence of dark matter, the gravity exerted by the mass of stars, gas, planets, and moons in galaxies would not be enough to prevent them from flying apart as they move rapidly.<\/span><\/p>\n

Alonso-Alvarez explained that when galaxies first merge, their supermassive black holes are far apart. Eventually, they begin their journey toward the center of the merging galaxies, which will become the site of their own merger and the heart of the newly formed galaxy conglomerate.<\/span><\/p>\n

This journey is facilitated by the loss of energy from black holes and occurs in three distinct stages.<\/span><\/p>\n

In the first stage, the black holes rush past many stars and interact with them gravitationally. Due to this interaction, the black holes change speed and slow down. This loss of speed allows the concentration of mass at the center of the merger to exert a gravitational effect on the black holes, causing them to move towards each other quite slowly.<\/span><\/p>\n

This energy loss continues to play a major role after the supermassive black holes travel the last 3.3 light years and form a binary system, the third stage of this process. At this point, the voids orbit each other, generating gravitational waves. As these waves spread out from the binary system, they carry away angular momentum, thus losing rotational kinetic energy.<\/span><\/p>\n

This very efficient loss of energy causes the two black holes to move closer together, and their merger becomes irreversible. The tighter their orbits become, the faster they emit gravitational waves. Eventually, as the supermassive black holes get closer and closer, their gravitational influence takes over, and they collide.<\/span><\/p>\n

The second stage is the stage between the transfer of energy to the stars and the loss of energy through gravitational waves.<\/span><\/p>\n

Interaction with stars is only really effective when black holes are very far apart, that is, at distances greater than a parsec, and gravitational radiation only appears when they are closer than fractions of a parsec.<\/span><\/p>\n

Alonso-Alvarez and his colleagues suggest that when supermassive black holes reach distances of 3.3 light years and can no longer transfer energy to stars, dark matter takes over and begins to extract energy through a process called “dynamical friction.”<\/span><\/p>\n

If black holes move through this dense \u201cdark matter,\u201d they create friction similar to the friction of an object moving through a viscous fluid. If you model dark matter as a fluid, the interactions between dark matter particles give it a high viscosity. The high viscosity of a normal fluid indicates how difficult it is for an object to pass through it. In this case, this friction is created only by gravity. It never interacts with the black hole through any force other than gravity.<\/span><\/p>\n

Without the scattering of dark matter, this mechanism simply wouldn’t work. The reason for this is that the energy that black holes lose through friction, and dark matter goes into increasing the speed of dark matter particles. If there were no viscosity, dark matter particles would be scattered far away from this finite parsec region.<\/span><\/p>\n

This would mean that after a short time there would be no more dark matter left in this central region to create the necessary friction. However, if there is self-interaction of dark matter, there would be a redistribution of this energy between the particles in the central region of the galaxy, so that the dark matter does not dissipate.<\/span><\/p>\n

Dark matter interactions with supermassive black holes could also explain calculations of dark matter halos around galaxies, whose shapes cannot be fully explained by \u201ccold dark matter\u201d models. These models assume that this mysterious matter moves slowly (hence its name \u201ccold\u201d) and does not interact with itself. If Alonso-Alvarez and his colleagues\u2019 theory of dark matter mediators is correct, it may require a departure from the cold dark matter theory.<\/span><\/p>\n

Additionally, an unknown force-carrying particle is needed to mediate interactions between dark matter particles, and this study gave the team some clues about the nature of this particle. A force-carrying particle, or boson, acts as a mediator, helping other particles interact. For example, the electromagnetic force uses photons, or particles of light, as force carriers, while gravity is thought to use a boson called a gluon.<\/span><\/p>\n

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\nTwo supermassive black holes against the backdrop of the dark matter web that attracts them. Robert Lee. Space.com<\/span><\/em><\/p>\n

\u201cWe started with the very naive idea that dark matter self-interactions would just help solve this last parsec problem, but we didn\u2019t think we could predict which self-interactions would be favored,\u201d Alonso-Alvarez said. \u201cAs we worked and refined our calculations, we found that a very specific model was actually favored, in which the force carrier had a mass on the order of 1% of the dark matter particle\u2019s mass, and none of the other options we tried worked.\u201d<\/span><\/p>\n

“The calculations we did for this paper were purely analytical. We are now working on creating simulations to better understand this mechanism,” Alonso-Alvarez said.<\/span><\/p>\n

The physicist added that observational evidence for this theory could come from collections of high-precision rotating neutron stars called pulsar arrays, which scientists use as precision cosmic clocks. Crucial to this will be studying the background hum of space called the gravitational wave background, which is produced by mergers of supermassive black holes throughout the history of the universe.<\/span><\/p>\n

“You can look at the influence of dark matter and friction on this signal and make predictions about how the presence of dark matter changes the signal,” Alonso-Alvarez added. “I think the most interesting thing is that you can simultaneously compare this with evidence for dark matter self-interactions on galactic scales of many thousands of parsecs.”<\/span><\/p>\n\n","protected":false},"excerpt":{"rendered":"

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