The temperature variations in different regions of the Sun defy the laws of physics, according to Prof R Ramesh, a leading Indian solar astrophysicist. The Sun's core has a temperature of 15 million Celsius, while its surface, or photosphere, is about 5,500C. However, the corona, the outermost layer, can reach temperatures of 2 million C, sometimes even 40 million C. This phenomenon has puzzled scientists, as the corona continues to remain hot despite frequent eruptions, known as coronal mass ejections (CMEs), which release huge amounts of energy into space.
Prof Ramesh, who led a study on the latest findings from Aditya-L1, India's first solar observation mission in space, says the corona is where extreme weather events, such as solar flares and CMEs, originate. These events can cause geomagnetic storms, affecting life on Earth by knocking down power grids and disrupting weather and communication satellites. During normal times, the Sun launches two to three CMEs a day, but during the maximum solar activity cycle, which occurs every 11 years, there can be 10 or more in a single day.
Scientists have long been trying to understand how the corona maintains its high temperature, despite losing huge amounts of energy during CMEs. Prof Ramesh says that if the Sun's energy is not replenished, the star would lose all its energy, and Earth would plunge into an irreversible deep freeze. However, since this is not happening, it means there must be a mechanism by which the corona is able to maintain its temperature. According to Prof Ramesh, this mechanism is due to two factors: the bubbling, boiling motions on the Sun's surface, which generate waves that carry energy to the corona, and the tangled magnetic field lines in the Sun's atmosphere, which constantly snap and reconnect.
The study, published in the Astrophysical Journal Letters, found that the second system, the tangled magnetic field lines, supplies most of the energy to the corona. Prof Ramesh says that while the waves generated by the bubbling motions on the Sun's surface do contribute to the energy, their contribution is very little, supplying only 7% of the energy requirement. The remaining 93% comes from the Sun reconfiguring itself and replenishing the lost energy. The study analyzed a very energetic CME that took place on 5 August 2024, and found that in 10 hours after the event, the tangled field lines were able to reconnect, and the corona's energy was reconfigured.
These findings provide an important benchmark for future studies into the potential energy generation mechanisms in the Sun's atmosphere. Prof Ramesh says that the data will help answer fundamental questions of physics that defy logic. The study's results are a significant step forward in understanding the Sun's mysteries, and will likely have implications for the field of astrophysics. As India's solar mission continues to explore the Sun, scientists are eager to uncover more secrets about the star at the center of our solar system.
