According to foreign media reports, our human world is bathed in light. First of all, the illuminated side of the earth receives about 10 trillion photons per second per square centimeter from the outer layers of the remote natural giant thermonuclear reactor, which we call the sun. Then there are photons that travel around in any cubic centimeter of open space. Some are microwaves left over from the thermal explosion of the universe 13 billion years ago. Others are photons produced by distant stars and various astrophysical phenomena in the universe. < / P > < p > we are also surrounded by artificial electromagnetic radiation from the earth. We warm and soft human beings are walking strong infrared beacons. Our amazing chemical metabolism turns energy into heat and radiates photons into the environment. If you put on a pair of glasses that can sense the mid infrared wavelengths of the electromagnetic spectrum, you will see a world full of light: there is your own light, there is the light produced by your cat and dog, your pet parrot, even the tiny muscle of flapping wing insects. < / P > < p > however, as we look at the vast universe, it is increasingly obvious that our world of light seems a little unusual in the universe. One of the most glaring hints is that when the sun goes down, our world falls into darkness. If we live in a truly infinite and unchanging universe, we may look up and see stars everywhere, and all the stars are stacked so that light should be visible everywhere. < / P > < p > is a little contradictory, isn’t it? In cosmology, we call it the “orbs paradox”, which was proposed by the German astronomer obers in 1823. Although orbs himself tried to solve this long-standing problem mathematically, he failed to provide a good answer to the question why most of the universe is dark. Finally, it was Edgar Allan Poe who, for the first time, gave a plausible explanation for the obers paradox in 1848. Poe’s qualitative analysis is that perhaps the universe is too young to fill the sky with light. There are some subtleties in the modern interpretation of the orbs paradox, but it can be attributed to the fact that we do not live in an infinite and immutable universe. Not only is the universe limited in age, but the history of making stars (with finite lifetimes) is complex, and the universe is expanding, diluting the intensity of light that reaches us from afar. As a result, the sky above us looks uneven, and most universes especially like to “swallow” photons compared to the everyday environment in which we live. < / P > < p > but the story doesn’t end there because there are some oddities in the history of stars. First of all, it has to do with the actual formation of stars. Even though we don’t know the whole process of stellar collapse or galactic condensation, we don’t know the whole process of stellar collapse. < p > < p > research over the past 30 years has shown that the “star making” activity in the whole universe reached a peak about 10-11 billion years ago. Since then, although there are still new stars forming in the universe from time to time, the frequency of star formation has not been as high as before. Basically, almost all the stars that the universe can make – about 95% of them – have been built. In the future, there will be fewer and fewer new stars, and there will be occasional galaxy mergers or other emergencies. However, there is still a big question. What limits the number of stars the universe can make? This is also an enduring topic of astronomical discussion, especially the topic related to the stellar composition of individual galaxies. For example, our current cosmological paradigm (or a paradigm recognized by most scientists) is that we live in a dark matter dominated universe, and in this dark matter dominated universe, the largest galaxies should be recently formed, consisting of low-level, gravitationally driven merging small galaxies. But if you look at those massive galaxies, you’ll find that most of them are made up of older stars, which means they’ve been around for at least a long time. < / P > < p > to explain this, astronomers have introduced the concept of “queuing”. In the process, some activities inhibit or prevent the formation of new stars in the galaxy. As expected, you need a very powerful mechanism to suppress or stop star making on such a large scale, and then the most suspect factor behind this is the supermassive black hole at the center of most galaxies. These black holes will devour everything around them. As matter approaches the surface of a black hole, it releases energy in the form of photons and particles. This outward radiation of energy just blows away the interstellar gas that could have cooled down and condensed into new stars, thus inhibiting the formation of new stars. Of course, we don’t know the specific process very well. But a new and intriguing clue is that the mass of supermassive black holes seems to be related to the total mass of the stars in their galaxy. This clue is very surprising, because even a supermassive black hole with a mass more than a billion times the mass of the sun is about the same size as a sun. So it’s possible that a galaxy tens of thousands of light-years in diameter is actually closely related to the very small dot in its center. One explanation for this is that there is a pulse feedback mechanism. If a black hole grows by swallowing the same interstellar gas as the formation of a new star, this process will also cause the energy radiated out to be engulfed by the black hole itself, and then the energy radiated and absorbed will blow away the interstellar gas that makes the black hole grow up, and at the same time, it will stop the star making activities of the whole galaxy. Under this mechanism, the mass of the black hole and the total number of stars in the galaxy grow synchronously throughout their life cycle. This also contributes to one of the strangest features of black holes. Although the universe is “unidirectional” – space and time bend toward the surface of a black hole, and nothing can escape, black holes can also explain some of the brightest and far-reaching phenomena observed in the universe. These phenomena, in turn, may greatly limit the number of stars in the universe; they also play a role in inhibiting the accumulation of light in the universe. There is an old saying that there is no light without darkness. For the universe, we can say the same thing: without light, there is no darkness. (Henglin) < A= target=_ blank>Skip to content