An international team of scientists has detected a source of a radio signal similar to a heartbeat in the Sun’s atmosphere and determined the mechanisms of its occurrence. The discovery is reported in an article published in the journal Nature Communications.
The researchers analyzed the results of microwave observations of a solar flare that occurred on July 13, 2017, which were carried out using the Expanded Owens Valley Solar Array (EOVSA) radio telescope in California. EOVSA is used for routine observations of the Sun over a wide range of microwave frequencies from 1 to 18 gigahertz (GHz) and is sensitive to radio emissions emitted by high-energy electrons in the Sun’s atmosphere that are excited by solar flares.
Solar radio bursts are intense bursts of radio waves often associated with solar flares and characterized by repetitive signals. However, the origin of these repeating patterns, also called quasi-periodic pulsations (QPPs), has long been a mystery.
The team identified a strong quasi-periodic ripple signal at the base of a layer of electric current that stretches more than 25,000 kilometers through the flare region, where opposing magnetic field lines converge, break, and reconnect. This phenomenon is known as magnetic reconnection, which releases the energy that powers the flare.
The researchers also found a secondary source of “heartbeat” that is located along the stretched current sheet, which pulsates in the same way as the main source of QPP, and is closely associated with it. The simulation showed that magnetic islands or bubble-like structures are formed in the current sheet, whose movement to the flare region occurs with a quasi-periodic character.
According to the authors, the study made it possible to accurately determine the origin of QPP in solar flares and prompts a revision of the interpretation of similar events recorded earlier and their influence on solar flares.