Scientists at the Indian Institute of Astrophysics (IIA), using data obtained from the Visible Emission Line Coronagraph (VELC) payload onboard Aditya-L1, found unambiguous observational evidence that interactions between the magnetic field lines are primarily responsible for maintaining the energy budget in the sun’s atmosphere.

It found that the higher temperature in the corona as compared to the solar surface is also due to similar interactions.

According to R. Ramesh, senior professor at IIA and principal investigator for VELC, the shine of the sun that we see every day is due to the continuous generation of energy in the interior of the sun, which is transported outwards.

“So, it’s quite natural to expect that the sun’s temperature should decrease from the surface to the outer layers in its atmosphere. But in reality, it does not happen. The surface of the sun, called the solar photosphere, which is seen every day with the naked eye, is at a temperature of approximately 5500 degrees. Compared to this, the temperature of the outer atmosphere of the sun, called the solar corona, is approximately two million degrees,” Dr. Ramesh said.

He added that the temperature of the corona can increase upto forty million degrees during energetic eruptions.  

The solar corona can be seen with the naked eye only during a total solar eclipse.

“One of the long-standing mysteries in solar astrophysics is how the energy budget is maintained in the sun’s atmosphere despite the occurrence of eruptions like the coronal mass ejections (CME) during which large amounts of energy are released by the sun,” he said.

According to the scientists there can be several CMEs even on a single day.  

“So, if the energy loss from the sun is not replenished intrinsically, it can completely lose all its energy, and the earth would plunge into an irreversible deep freeze,” they said.

Dr. Ramesh said the results from this observation can provide an important benchmark for future studies and added that one of the key inputs for the study came from data obtained with the network of identical low-cost solar radio spectrographs, installed in several countries across the globe. One such radio spectrograph is operated by IIA in the Gauribidanur observatory.

V. Muthupriyal, project scientist for VELC, said that since energetic eruptions in the sun’s atmosphere can happen at any time, continuous and uninterrupted observations with VELC is a boon for not only solar physicists in our country, but the entire world.