Related papers were published in the internationally renowned academic journal Nature-Communication at local time 1 1.9. The author is a researcher at Nanjing Purple Mountain Observatory of China Academy of Sciences, Fan.
Huang Xiaoyuan pointed out that cosmic rays are also the most well-known messenger particles besides electromagnetic waves, which bring us a lot of information outside the solar system. The study of cosmic rays is also extremely important for the indirect detection of dark matter, which may lead to new physics.
Cosmic rays are high-energy particles that originate outside the solar system and will eventually reach the earth. Previously, people thought that the cosmic rays of the Milky Way were distributed in the Milky Way in a relatively smooth "sea" shape.
Specifically, cosmic rays in the Milky Way can be accelerated by the shock wave of supernova remnants or the stellar wind of massive stars. These charged relativistic particles will then diffuse in the galactic magnetic field, and may undergo the processes of re-acceleration, convection, collision and fragmentation and energy loss, which will eventually lead to the cosmic ray "sea" in an approximately stable state on a large scale, with relatively smooth spatial distribution and no mutation.
However, there are still some uncertainties about the accelerating source of cosmic rays.
"Within the Milky Way, it is generally believed that supernova remnants are good candidates for accelerating sources, but theoretical research believes that supernova remnants are more difficult to accelerate cosmic rays to PeV. Because cosmic rays collide with interstellar media to produce gamma rays, gamma rays can be used to study the properties of cosmic ray sources. " Huang Xiaoyuan said.
However, in order to understand the very high energy cosmic ray (TeV-PeV), it is necessary to further explore the different emission components in the central molecular region (CMZ).
Huang Xiaoyuan and his colleagues reanalyzed the galactic CMZ data of Fermi Wide Field Telescope and determined a GeV-TeV cosmic ray component (low energy component from the early TeV-PeV source). The author believes that this supports the view that there is a high-energy particle accelerator in the center of the galaxy. It is also found that the estimated energy density of CMZ cosmic rays is lower than that of the "sea" component of cosmic rays. They think this shows that there is a barrier to prevent particles from penetrating from the cosmic ray sea to CMZ.
"In 20 16, Hess experimental group analyzed the diffuse gamma-ray radiation near Yin Xin, and thought that the past activities of the Yin Xin black hole could accelerate cosmic rays and accelerate them to PeV. This is the first possible PeV cosmic ray source discovered by humans. " Huang Xiaoyuan said. The acceleration source is probably related to the activity of supermassive black holes with silver nuclei.
γ -ray spectrum of cosmic ray radiation accelerated by silver nucleus
In this published study, the research team used the gamma-ray data of Fermi satellite to confirm the existence of the silver nucleus cosmic ray accelerator at low energy in terms of energy spectrum distribution and spatial distribution. The research team proved the low-energy counterpart of PeV accelerator found by Hess et al. in the lower energy band.
"In addition, we were surprised to find that the diffuse cosmic ray background in the Milky Way was blocked and could not spread to the area near the Silver Heart. Therefore, the cosmic rays near the silver heart are mainly composed of cosmic rays newly accelerated by the past activities of the silver heart. " Huang Xiaoyuan said.
The research team found that the cosmic ray energy density in the central molecular cloud near the center of the Milky Way is lower than that in the cosmic ray "sea" outside the quantum cloud. This means that the central molecular cloud prevents the high-energy particles in the cosmic ray "sea" from penetrating into the region. The physical reason may be that the magnetic field intensity in the molecular cloud is higher, shielding cosmic ray particles in the molecular cloud.
Similar magnetic shielding effect has been observed in our solar system, which is the solar modulation effect of cosmic rays. Our galaxy as a whole is also similar to such a barrier, keeping low-energy cosmic rays out of the river.
The research team concluded that 3D modeling of the galactic center in the future may help us to understand the origin of cosmic rays and their propagation in the galactic center.
Proofreading: Zhang Yan