Experimental Simulation of Photoionization Processes in the Neighborhood of the Black Hole Done by Team of Academician Zhang Jie Has Made Significant Headway

Exploring the mysteries of the black hole, neutron stars, jet flow and other celestial phenomena is an important issue in astronomical research. The black hole has a huge gravitational field, which even light cannot escape. Therefore, people fail to observe its internal motion state directly. In order to study the black hole, astronomers focus their attention to the accretion disc in the neighborhood of the black hole. Near the inner loop of the accretion disc, the gravity of the material flow can heat the material to the extremely high temperature, and the generated X-ray radiation will ionize the surrounding material and emit light. It is through the photoionization spectra that the astronomers indirectly study the black hole with certain theoretical model. Therefore, the identification of the spectra and the validity of the theoretical model are crucial for understanding the black hole.

In the past two years, the research team led by Academician Zhang Jie carried out the experimental research on the photoionization processes and the emitted X-ray radiation with Japanese and South Korean scientists by applying “ShenguangⅡ” of National Laboratory on High Power Laser and Physics, Shanghai and “Gekko XII” laser facility of Osaka University, Japan. It is discovered that 1.84keV Spectrum of Si may not be the forbidden transition lines recognized by astronomers, but stems from another type of transition which emits the spectra coinciding with the “forbidden transition” spectra astronomically observed. The spectra resemble those observed from the binary stars Cygnus X-3 and Vela X-1. But the analysis on the characteristics of the spectra components in this experiment by using Non-LTE model gives the explanation quite different from that of astrophysicists. The results attracted the attention of scientists who think that the experiment will correct some of people’s understanding of the material structure around the compact objects. In addition to the simulation of the photoionization process in the neighborhood of the black hole, the team also carried out the laboratory simulation of processes of the celestial jet flow and collision-free shock wave. The latter has the significant role in understanding the generation mechanism of high-energy cosmic rays.

Part of the previous work has been published in Nature Physics lately, and its internet edition has been published on October 19, 2009 ((DOI:10.1038/nphys1402)). The project has been aided financially by National Basic Research Program of China (973 Program).