In terms of star density, the region where the solar system is located can only be regarded as the "outskirts" of the Milky Way at best, because the distribution of stars in the Milky Way is not uniform, and the closer to the central region, the higher the density of stars, so that in the central region of the Milky Way, the density of stars can reach millions of times, or even more, in the region where the solar system is located.
In the past few days, scientists have been exploring what secrets are hidden in the center of the Milky Way, and there have been a lot of discoveries, including of course, there are some mysterious phenomena, such as in a study related to cosmic rays, scientists found that there is a mysterious barrier, let's take a look at what is going on.
In short, cosmic rays are a kind of charged high-energy subatomic particles in space, most of which are protons, and a small number of α particles (helium nuclei), electrons and other heavier elements. They are very common in the Milky Way due to the high-energy activities of various celestial bodies in the universe or the high-energy processes of the evolution of celestial bodies, which have the potential to produce a large number of cosmic rays.
According to the theoretical model, since cosmic rays are charged particles, when they propagate in the Milky Way, they will be repeatedly accelerated or decelerated by various magnetic fields in the galaxy, and their direction will change randomly, so theoretically speaking, the distribution of cosmic rays in the Milky Way should be smooth and relatively stable, but is this really the case? In this regard, a research team led by Huang Xiaoyuan, an astrophysicist at the Chinese Academy of Sciences, gave a negative answer.
Although we cannot directly observe cosmic rays, because cosmic rays interact with some interstellar media (such as gas and dust) from time to time during their propagation, there is a certain probability that gamma-ray photons will be released in the process, so through this phenomenon, we can indirectly observe cosmic rays in the Milky Way.
In this study, scientists analyzed observations from the Gamma-ray Large Area Space Telescope and revealed a surprising phenomenon: the density of cosmic rays in the Milky Way's "Central Molecular Zone" is significantly lower than the Milky Way's average, and there seems to be a mysterious barrier there that prevents cosmic rays from their outer side from propagating to their interior.
(↑ The "central molecular cloud" is a material-dense region in the central region of the Milky Way, containing a large amount of gas and dust, spanning about 1600 to 1900 light-years)
It is important to know that there is a supermassive black hole at the center of the Milky Way, and there is also a large amount of cosmic ray acceleration and release process in the nearby high-energy environment, so a reasonable guess is that this barrier should be "one-way open", simply put, it only allows the cosmic rays on its inner side to "go out", and does not allow the cosmic rays on its outer side to "come in", because if this is not the case, the density of cosmic rays in the "central molecular cloud" should not be as low as we observe.
It has to be said that such a phenomenon is really imaginative, and a fascinating speculation is that there may be a highly technologically advanced alien civilization there, and this barrier is their masterpiece, after all, this barrier is strong enough to block cosmic rays, and of course it can also be used to ward off other threats.
However, in the absence of conclusive evidence, scientists will not easily adopt the option of "extraterrestrial civilization", so how did this mysterious barrier in the central region of the Milky Way form from the perspective of natural formation? In this regard, scientists have given a variety of explanations, and as far as the current situation is concerned, there are two main types of high recognition.
One view is that the gas in the "central molecular cloud" may collapse locally under the influence of gravity, which may lead to an increase in the density of the gas in the local area, and these high-density gases can compress the magnetic field lines, which in turn will increase the strength of the local magnetic field, after which the enhanced magnetic field will exert a strong force on the cosmic rays, causing them to change their path, thus forming a natural barrier that prevents most of the cosmic rays from entering the central region of the Milky Way.
Another view is that in the solar system, the "solar wind" (i.e., the high-speed stream of charged particles released by the sun) has a significant blocking effect on cosmic rays from deep space, and in the central region of the Milky Way, a large number of stars may also produce a "galactic wind" similar to the "solar wind", but on a much larger scale, thus blocking most of the cosmic rays.
(↑ "Solar wind" blocking cosmic ray image)
It should be noted that as far as the current situation is concerned, this can only be said to be reasonable speculation, whether this is really the case, still needs further research, all in all, there are still too many secrets in the galaxy waiting for us to explore.