According to comprehensive media reports, in a new study analyzing data from the Fermi Gamma-ray Space Telescope, the researchers compared the cosmic ray density between this sea of particles and the center of the galaxy, and unexpectedly found that although the center of the galaxy continues to blow high-energy radiation storms into space, However, there is a region that blocks most of the cosmic rays, making its density significantly lower than that of the rest of the Milky Way. The force and mechanism of this barrier are still a mystery.
The center of the Milky Way is 26,000 light-years away from the earth. From the perspective of the earth, it is located in the constellation Sagittarius. There is a black hole with a mass of 4 million times the sun in the center of the galaxy, surrounded by stars. The density of stars around the galactic black hole is 1 million times the density of stars within 1 light-year around the solar system. There is also a huge natural particle accelerator hidden in such an extreme place (probably the black hole), which can accelerate protons and electrons to near the speed of light. Such high-speed particle streams are cosmic rays. Cosmic rays also travel across galaxies, since the centers of nearly every large galaxy generate streams of such rays. When cosmic rays interact with the galaxy’s magnetic field, they form a sea of roughly uniform rays that “soaks” the entire galaxy.
We can’t see cosmic rays directly, but they produce gamma rays when they hit particles of matter. So the researchers used an indirect method, by observing gamma rays, to understand the difference in the density of cosmic rays in various parts of the Milky Way. The researchers found that the density of cosmic rays drops off sharply just inside the boundary of the Milky Way’s central region. It seems that there is an invisible barrier there, which only allows cosmic rays generated in the center of the galaxy to leave, but does not allow external rays to enter. This is a very strange phenomenon, and the researchers speculate that there are several possibilities. One is that the dense dust and gas cloud near the galactic core collapsed by itself, compressing the magnetic field around the galactic core, and then forming a barrier that external rays cannot enter.
The other is that the stellar wind generated by a large number of stars near the galactic center forms a “wall” that blocks the external rays, just like the solar wind, pushing back the forward cosmic rays. Scientists say that if we better understand the behavior of cosmic rays, we can further clarify how the Milky Way works and speculate on other interesting behaviors of distant objects such as blazars.