B'luru scientists shed light on 142 y/o solar puzzle

An international team of scientists including two Bengaluru astrophysicists on Friday shed new light on a 142-year-old solar mystery and in the process opened up a fresh window to look at one of the biggest enigmas associated with the Sun.

The team comprising researchers from the Indian Institute of Astrophysics found out how, solar spicules – small-scale plasma jets about a million of which are present on the Sun at any moment – are born and die on the star.

The discovery may help unravel one of the biggest yet-to-be-solved mysteries in astrophysics - how the temperature in solar corona increases.

Corona is the outer atmosphere of the Sun, which extends outward for several million kilometers beyond the solar surface. Though the temperature at the core of the Sun is close to 15 million degrees Celsius, it drops to mere 5,700 degrees at the solar surface (photosphere).

However, above the photosphere, the temperature starts to increase again with height, reaching one million degrees or more in the corona. What causes such a temperature rise in corona despite moving away from the core remains a mystery.

Tanmoy Samanta who did his PhD at IIA, his supervisor and senior IIA scientist Dipankar Banerjee and their colleagues from China, USA and Europe believe that solar spicules provide them with an opportunity to crack the riddle.

Discovered by Father Secchi in 1877, solar spicules are small-scale (3000-5000 km long and 200-500 km wide) magnetized geyser-like plasma jets found ubiquitously in the chromosphere, the interface between the photosphere and corona.

“Studying them are difficult as each spicule – from formation to collapse – lasts only a few minutes though at any moment there are about a million of them on the Sun,” Samanta told DH.

Old generation solar telescopes were not sophisticated enough to study such features. The breakthrough came when the team carried out observations with the 1.6-m Goode Solar Telescope at the Big Bear Solar Observatory, California, the world’s largest solar telescope that is currently operational.

The telescope not only observed copious spicules at great detail but also measured the magnetic fields in the photosphere at high-spatial resolution.

“The spicules were generated from two magnetic fields of opposite polarity, which annihilate each other generating kinetic and heat energy. This leads to the creation of the plasma jets, which in turn possibly contribute to enhanced corona temperature. But we need to study more to be certain,” Samanta explained. The findings have been published in the journal Science on Friday.

The scientists would have to now carry out advanced computer simulations and theoretical investigations based on these new observational results to resolve the long-standing coronal heating problem.