Astrophysicists never tire of discussing when and how supermassive black holes emerged. One thing is certain: They emerged in and through galaxies. But what if galaxies themselves were the product of black hole activity? This is how the “impossible” galaxies that have scientists on the brink of extinction could have emerged.

Peering into the past of the universe, the James Webb telescope is seeing unexpectedly mature galaxies with many stars. How did they form hundreds of millions of years after the Big Bang? The authors of a new study published in the prestigious Astrophysical Journal Letters believe they have found the answer.

Researchers have identified supermassive black holes (MBLs) as the architects of galaxies and large-scale star producers. But the question immediately arises as to how black holes manage to form. To answer this, it is possible that something in the fundamental tenets of cosmology (the science of the origin and evolution of the universe) will need to be “tweaked.”

Before dawn

It is believed that immediately after the Big Bang, mass was distributed almost evenly throughout space. At least, much more evenly than it is now, where relatively dense galaxies are separated by vast, deserted chasms. But the key word here is “almost.” The formation of galaxies began with primary seed heterogeneities. Where the density was slightly higher, gravity was also higher. These centers of gravity pulled on matter, which made the attraction stronger, and so on. This is a great example of positive feedback; we’re going to need this concept!

This is how giant protogalactic clouds of dark matter and primordial gas (hydrogen mixed with helium) came into being. At each point in the cloud, the gravitational forces of all the surrounding masses of matter were added. This total attraction was strongest at the center of the protogalaxy. This was where the large masses of gas were drifting. This motion was similar to the pulling of water currents towards the bottom of the ship. Here, instead of just the gravity of the Earth, the collective gravity of the entire protogalaxy worked.

In the interiors of these giant clouds, gravity also pulled matter into clumps, increasing small random inhomogeneities. This is how stars formed from the primordial gas.

The researchers made a small but very important addition to this standard scenario. They hypothesized that supermassive black holes formed very early in the centers of protogalaxies. Perhaps tens of millions of years after the Big Bang, the authors suggest, or even before the first stars appeared. Supermassive black holes nest in almost all large galaxies, but they are not generally thought to be that old.

Warm hearts

The behavior of the SMCHD is well known to astronomers. Any matter that gets too close to the black hole is captured by its gravity and enters orbit around the “hunter”. Thus, a black hole acquires a disk-shaped cloud of matter rotating around it – an accretion disk. Each layer of the disk rotates at its own speed: the closer to the black hole, the faster. Near the event horizon – the “surface of no return” of a black hole, where there is no return – this speed is comparable to the speed of light.

Since the speeds of adjacent layers are different, friction occurs at the points of contact. And since this speed is very high, friction is terrible. It heats the substance to hundreds of millions of degrees. It is ten times hotter than the center of the Sun. At such a temperature, even atoms cannot exist: they are disintegrated into nuclei and electrons, and the substance turns into plasma. Every kilogram that enters this infernal furnace releases tremendous energy. About 10 percent of Mc ² the theoretical limit of what can be extracted from matter. It is a “generator” ten times more efficient than the thermonuclear reactions inside stars.

Also, frictional gas flows lose their torque. Closed orbits turn into spirals. The lower part of the disk gradually sinks into the black hole. However, most of the red-hot disk-like cloud is above the event horizon, thus emitting a radiation stream into the surrounding space. Paradoxically, even some of the matter is thrown out of the accretion disk. The fact is that huge electromagnetic fields arise in the plasma cloud, turning the disk into a giant particle accelerator. They throw out jets of particles at orbital speed, and even the gravity of the central black hole cannot contain them.

This is a classic picture of the functioning of quasars, the most powerful sources of radiation in the universe. On a smaller scale, the same processes occur in the nuclei of many galaxies. Even the black hole at the center of the Milky Way, which weighs “only” four million suns, has its own accretion disk. Fortunately for us, it is small and relatively weakly radiating. If the nucleus of the galaxy were more active, life on Earth would be impossible due to the powerful radiation flows.

Changeable blur

The answer is simple. According to the authors, all this enlightenment began in very young protogalaxies. The mass of stars in a typical galaxy today is comparable to the mass of interstellar gas, and at that time there were no stars or very few. Almost all the material that would later become stars was present in gaseous form. So there was much more gas around the black hole than in the modern mature galaxy or even in the oldest known quasars.

Such a neighborhood could not be called a gas cloud for nothing. Powerful radiation and streams of charged particles emitted by the accretion disk hit the surrounding gas. They tore and sheared the clouds, forcing the matter to literally explode (in scientific terms, creating turbulent flows).

What was the future fate of this murky gas? This is where the fun begins. Despite its abundance, stars were born from it. And they were born in the middle of a hurricane, and at an accelerating rate.

Star factory

Stars form where there is inhomogeneity, where there is compression. They are the seeds from which gravity draws matter. Compressions (also rarefactions) have occurred in commercial quantities in fragmented, fragmented gas clouds.

Not all the gas from the torn clouds became stars. Some of it fell onto the accretion disk and fed it. This made the black hole even more active, and the surrounding clouds collapsed even faster; the circle was closing.

Such a closed loop, in which the process accelerates itself, is called positive feedback. Anyone who has ever made a snowman knows: a pile of snow that fits in the palm of your hand grows almost to the waist in a few steps. After all, the larger its surface, the more snow will stick to it in one turn, which will increase its surface even more. Another example is the spread of a new infection. The more people get sick, the more people will be infected through contact with them, who will infect more people. In the spring of 2020, Russians could watch dozens of confirmed COVID-19 cases turn into thousands in a matter of weeks.

In general, if something (snow, disease cases, or stars in the galaxy) becomes abundant very quickly, it is time to suspect positive feedback. What did astronomers do?

But common sense reminds us that positive feedback eventually ends. In a world of finite resources, nothing can grow forever. The snowball will grow in size and stop moving. The majority of the population will become immune, and the spread of the virus will slow. The reserves of primordial gas are depleted, and there is nothing to form new stars with.

Gone like the wind

In fact, the situation is even more interesting. As the gas clouds are depleted, the turbulent flows have changed their behavior. These jets no longer break up into protostellar clusters. They now flow from the center of the galaxy to the periphery and possibly beyond.

It’s natural to ask: Why has the behavior of gas flows changed so much? There’s some pretty subtle physics here, but let’s try to explain it in two words. In a “star factory,” gas not only has to flow through local seals, but it also has to be effectively cooled. First, you can’t build a star from very hot matter: the increased pressure would stop the protostellar cloud from compressing. Second, the energy from the black hole has to be channeled somewhere so that the gas stays in place and doesn’t fly away.

When the gas in the protogalaxy became too thin, the previous cooling mechanisms stopped working. The “star factory” shut down and a “capital flight” began. According to the authors’ calculations, this dramatic transition occurred when the universe was about a billion years old.

Seeds of the future

So galaxies matured early because the black holes at their centers matured even earlier. So how did black holes do it? Aren’t we just moving the problem to the other side of the table instead of solving it?

Astronomers still don’t know how supermassive black holes are formed. One theory suggests that it is a series of merging black holes of stellar mass. The second is formed by heated stars. It is clear that such a scenario does not suit us. After all, the authors already have supermassive black holes, while there are still very few stars in the galaxy.

Another version is that supermassive black holes grow from “heavy seeds”. This is how astronomers poetically call black holes with masses of up to 100,000 suns, which form from dense clouds of gas. Such a “seed” can grow to millions and billions of suns by drawing in surrounding gas. This theory somehow copes with supermassive black holes that appeared 500 million years after the Big Bang (quasars from this era are known to observers). But there is no question of the first 100 million years of the universe’s existence.

What is the secret of SMCHD’s early maturation? The authors offer several solutions. One of them is the increasing number of primordial black holes in the universe.

In the beginning there were holes

Primordial black holes are literally the first astronomical objects in the universe. They formed in the first seconds after the Big Bang. Before atoms existed, let alone galaxies and stars.

Where did they come from? We’ve talked about the primordial inhomogeneities that gravity causes to galaxies. Some of these inhomogeneities just happened to be so dense that they instantly turned into black holes without any additional bits of matter. These black holes are called primordial.

Unfortunately, observers are not given birth certificates for black holes. It is almost impossible to tell whether a black hole has existed since the first second of the universe’s existence, or whether it was born much later. Therefore, no black hole is known to date that can be reliably recognized as primary. On the other hand, theorists believe that primordial black holes are real. Their existence is an inevitable consequence of any reasonable cosmological theory.

According to cosmologists, primordial black holes had a wide range of masses, from dust particles to supermassive giants. It is clear that powerful objects are less common than lungs. This law is always at work when gravity shapes lumpy matter. It is easy to trace even in the solar system: there are few planets, there are much larger asteroids, even smaller ones, and every little thing, like meteoroids, cannot be counted. A short formula will help you remember this principle: There are more cockroaches than elephants.

But how exactly more? How many black holes – “cockroaches” were there for one “elephant”? And how many “elephants” were formed in the visible universe?

There is no definitive answer to this question. Theory allows for several options that do not contradict observations. In the simplest models, very few massive black holes are formed. But in fact, it is possible that there are no fewer than galaxies. And then it can be assumed that the primary black holes, or even ready-made SMCs in the nuclei of galaxies, become “heavy seeds”.

But this is the only option. The authors mention the possibility of “bending” the distribution of initial inhomogeneities. Then the black holes in the centers of galaxies will have time to grow without any primary “seeds”. There are other scenarios, even more exotic.