China News Service, Beijing, October 29 (Reporter Chen Su) The sun's outermost atmosphere, the corona, has long hidden a problem that has troubled the scientific community: The temperature of the corona is much higher than that of the sun's surface. How is it heated to millions of degrees Celsius? Recently, the China Institute of Atomic Energy, in collaboration with Beijing Normal University and other universities and research institutes, demonstrated for the first time the complete physical process of nanoflares heating the corona through magnetic reconnection, providing the first laboratory quantitative benchmark for the long-unsolved major scientific issue of "corona heating" and having important scientific significance for understanding the energy release mechanism in the stellar atmosphere and its impact on the planetary space environment.
The results were titled "Laboratory demonstration of coronal heating via magnetic reconnection during nanoflares" and were published in the top international physics journal "Physical Review Letters".
The inner core of the sun is about more than 10 million degrees Celsius, and the surface has dropped to about 5,500 degrees Celsius, but the temperature of the corona has risen again, returning to millions of degrees Celsius. In 1988, the "nanoflare" theory proposed by Parker proposed a possibility for the coronal heating mechanism. He believes that countless tiny magnetic reconnection events in the corona continue to convert magnetic energy into thermal energy, thereby continuously heating the corona. However, the generation mechanism of the tiny current sheets required to trigger these magnetic reconnection events still lacks direct verification. Recent observations have shown that Rayleigh-Taylor instability (RTI) is prevalent in coronal rain, prominence and other environments, providing a candidate mechanism for the self-organization formation of micro-current sheets, but there is still a lack of direct quantitative evidence at the nanoflare scale.
During this research, the team used the SG-II laser device to conduct a series of experiments. By modulating the target with strong laser irradiation, the magnetic reconnection phenomenon was generated in the laboratory. Through spectral measurements, it was determined that the temperature near the magnetic reconnection phenomenon actually increased. Through data simulation, it was confirmed that the temperature increase disappeared immediately after the magnetic field generation mechanism was artificially turned off, further confirming that magnetic reconnection is the dominant mechanism of abnormal temperature increase. Experiments and analysis show that the experimental conditions are comparable to the dimensionless parameters of the corona, proving that the cumulative heating of such processes can support the million-degree high temperature of the corona. In addition, the magnetic reconnection energy conversion mechanism and diagnostic technology revealed by this research can also provide a reference for understanding the magnetic field energy release in fusion experiments, and have important application prospects in nuclear industry-related fields such as inertial confinement fusion.
This research was jointly carried out by the China Institute of Atomic Energy and Beijing Normal University, Peking University, National University of Defense Technology, Beijing Institute of Applied Physics and Computational Mathematics, Harbin Institute of Technology, Inner Mongolia University and Shanghai Laser Plasma Institute of the China Academy of Engineering Physics. It received funding from the National Natural Science Foundation, the National Key R&D Program, the Innovation Fund of the Institute of Atomic Energy, the Strategic Priority Science and Technology Project of the Chinese Academy of Sciences and the Stable Support Project of the Ministry of Finance, as well as the computing support of the Beijing Supercomputing Center and the technical support of the Shenguang II device operation team.
What does the mystery of solar corona heating refer to?
As a common sense rule, the further away from the heat source, the cooler the temperature should be. But there is a counter-intuitive phenomenon on the sun: As the outermost layer of the solar atmosphere, the corona is the farthest away from the core area that generates heat, but its temperature is as high as millions of degrees Celsius, which is much higher than the photosphere (the surface of the sun seen by human eyes) with a temperature of more than 5,000 degrees Celsius. This abnormal phenomenon is the problem of corona heating, which was also listed as one of the eight unsolved mysteries of contemporary astronomy by the journal Science. As early as the 1940s, scientists identified highly ionized iron and calcium ions from the coronal spectral lines, confirming that the corona is a million-degree high-temperature gas.
The corona is not only a mass of hot gas, it is also the origin of the solar wind, where violent activities such as flares and coronal mass ejections occur. These activities jointly shape space weather and directly affect the safe and stable operation of satellites, communications, navigation and other system equipment. Therefore, the mystery of corona heating has also become a hot topic at the forefront of international research.
The results of this research provide the first laboratory quantitative benchmark for unraveling the mystery of "coronal heating", and also provide new experimental methods for basic research on space weather. Understanding the heating mechanism of the corona in the laboratory will help to determine the "temper" of the sun, further improve the accuracy of space weather forecast models, and reserve protection time for related equipment.
