In a new study published in the journal Nature Astronomy, scientists from the New Jersey Institute of Technology's Center for Solar-Terrestrial Research (NJIT-CSTR) have reported the discovery of a novel type of aurora-like radio emission emanating from a sunspot.
Sunspots are dark, cooler regions on the sun's surface that are caused by intense magnetic activity. The newly discovered radio emissions occur at frequencies ranging from hundreds of thousands of kHz to roughly 1 million kHz, which is much higher than the frequencies of typical auroral radio emissions on Earth.
The scientists believe that the radio emissions are produced by a process called electron-cyclotron maser (ECM) emission. ECM emission is a type of maser, or microwave amplification by stimulated emission of radiation. It occurs when energetic electrons are trapped in a strong magnetic field and forced to spiral around the magnetic field lines. As the electrons spiral, they release energy in the form of radio waves.
The scientists believe that the sunspot's intense magnetic field provides the ideal environment for ECM emission to occur. They also believe that the radio emissions may be powered by energetic electrons that are injected into the sunspot region from nearby active regions.
The discovery of this new type of solar radio emission has several important implications. First, it provides new insights into the origin of intense solar radio bursts. Second, it suggests that starspots on cooler stars could also be the sources of certain radio bursts observed in various stellar environments. Third, it raises the possibility that ECM emission could be a common feature of magnetically active systems throughout the universe.
The scientists say that their next step is to conduct a retrospective analysis of solar radio burst data to determine if any of the previously recorded bursts were instances of this newly identified emission. They also plan to conduct further observations of sunspots and other magnetically active regions on the sun to learn more about the conditions that are necessary for ECM emission to occur.
Journal Information: Sijie Yu et al, Detection of long-lasting aurora-like radio emission above a sunspot, Nature Astronomy (2023). DOI: 10.1038/s41550-023-02122-6