International Award for Dr. Yajie Chen

In his PhD thesis, the MPS scientist modeled which magnetic field structures in the solar corona trigger miniature solar flares, so-called campfires.

July 25, 2023

The International Astronomical Union has awarded Dr. Yajie Chen of the Max Planck Institute for Solar System Research (MPS) in Germany with the PhD Prize for 2022 in the category "Sun and Heliosphere". The worldwide association of astronomers thus recognizes the contributions of the young researcher to the understanding of magnetic fields in the corona, the Sun’s hot atmosphere. As part of his PhD at Peking University, Dr. Yajie Chen was able to study, among other things, which magnetic structures underlie miniature solar flares in the corona, known as campfires. ESA's Solar Orbiter first discovered this phenomenon a few years ago. It is apparently triggered by adjoining, aligned magnetic field lines that break up, reconnect, and release energy in the process. During his doctoral studies, Yajie Chen was a guest at the MPS for one year. It was here that he produced his seminal results on the campfires.

The Sun's corona is a tumultuous and extreme place. Trapped by strong magnetic fields, more than a million degrees of hot plasma with temperatures of more than a million degrees flows there; time and again, small and large flares and coronal mass ejections hurl radiation and particles into space. While many processes that occur in the corona are still not understood, it is clear that the magnetic fields there are a driving force. Tracing these and better understanding their influence on the turbulent, outermost layer of the Sun was the goal of Dr. Yajie Chen's doctoral research.

But the magnetic fields of the corona are extremely elusive: Unlike the magnetic fields at the visible surface, which space probes and ground-based telescopes have been routinely recording for decades, they have proven difficult to measure directly. A promising new method relies on the ultraviolet light emitted by tenfold ionized iron atoms in the corona. The wavelength of the emitted light is slightly altered by magnetic fields. In his doctoral thesis, Dr. Yajie Chen was able to show that this method can be used to reliably determine the magnetic field strength in active regions, areas with particularly strong and complex magnetic fields.

Another way to study the magnetic fields in the hot solar atmosphere is through elaborate computer simulations. Based on the magnetic fields measured at the Sun’s visible surface, the interaction of hot plasma and magnetic fields in the overlying layers can be simulated. In this way, a team of researchers including Dr. Yajie Chen has succeeded for the first time in modeling the processes that lead to solar campfires.

Already in the first months of ESA's Solar Orbiter mission, researchers discovered surprisingly many and small bright spots in images of the corona. They turned out to be particularly small flares and were henceforth referred to as "campfires." Observations that Solar Orbiter has since made from closer to the Sun confirm the finding. Researchers believe the campfires help to heat the corona to its unimaginably hot temperatures. Elaborate calculations and Dr. Yajie Chen’s data analyses now reveal the magnetic cause of the phenomenon. It occurs where magnetic field lines pointing largely in the same direction restructure, releasing energy in the process.

Using the same method, the young scientist turned his attention to another previously unexplained phenomenon: The wavelength of the characteristic radiation emitted by atoms in the corona is slightly shifted from that of atoms residing in a less extreme environment. Dr. Yajie Chen's computer simulations are the first to describe the interaction of all the responsible processes in one model, painting a much clearer picture of the phenomenon than before.

Dr. Yajie Chen studied at Peking University and received his PhD in solar physics. As part of his doctoral studies, he spent a year as a visiting doctoral student at the Max Planck Institute for Solar System Research. It was during this time, that he pursued his work on the solar campfires. Last year, Peking University honored Yajie Chen's dissertation with the Outstanding Doctoral Dissertation Award. Recently, Yajie Chen was also awarded one of the coveted Humboldt Postdoctoral Research Fellowships, which will allow him to continue his research at the MPS.

Each of the IAU's nine divisions annually awards the IAU PhD Prize to a young scientist for the worldwide most outstanding dissertation in their respective field. Since the members of the IAU only meet every three years for the General Assembly, the awards ceremony will not take place until next year in Cape Town, South Africa.


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