Using sound waves, scientists develop findings that challenge standard theories of solar convection

A team of solar physicists at NYU Abu Dhabi's Center for Astrophysics and Space Science (CASS) has made significant strides in unraveling the mysteries of solar convection, challenging established theories. Led by Research Scientist Chris S. Hanson, Ph.D., the researchers have focused on understanding the internal structure of the sun's supergranules, intricate flow patterns responsible for transporting heat from the sun's hidden interior to its surface.

In their groundbreaking study titled "Supergranular-scale solar convection not explained by mixing-length theory," published in the prestigious journal Nature Astronomy, the team delved into the observations obtained from NASA's Solar Dynamics Observatory (SDO) satellite's helioseismic and magnetic imager (HMI). By employing Doppler, intensity, and magnetic images, they successfully identified and studied around 23,000 supergranules.

Given the sun's surface opaqueness to light, the NYUAD scientists harnessed the power of sound waves to investigate the internal composition of these enigmatic supergranules - relying on a technique known as helioseismology. Sound waves, generated by smaller granules and omnipresent throughout the sun, have played a crucial role in previous studies using this methodology.

Analyzing an extensive dataset provided by the HMI, the researchers gained unprecedented insights into the up- and downflows within the supergranules responsible for heat transport. Determining that these structures extend approximately 20,000 km into the sun's interior (around 3% of its radius), they made a fascinating discovery. The downflows exhibited a notable weakness of about 40% compared to the upflows, indicating the presence of an unaccounted factor within the downflows.

The team, through rigorous testing and theoretical deliberations, has postulated that this "missing" or invisible component might involve small-scale plumes of cooler plasma, measuring roughly 100 km each, that transport material into the sun's interior. These plumes, however, escape detection by the size of the sound waves in the sun, consequently leading to the misinterpretation of weaker downflows. Consequently, the highly prevalent mixing-length theory, commonly employed to describe solar convection, fails to explain these newfound observations.

Dr. Shravan Hanasoge, research professor and co-author of the study, noted the significant impact of supergranules on the sun's heat transport mechanisms while acknowledging the resulting challenges faced in fully comprehending their intricacies. He expressed the hope that these findings would inspire further investigations into this fascinating phenomenon, catalyzing a revisit of existing assumptions about solar convection.

Carried out as part of CASS at NYUAD, the research collaboration included contributions from Tata Institute of Fundamental Research, Princeton University, and New York University. The utilization of NYUAD's high-performance computing resources greatly facilitated the achievement of these remarkable results. As scientists continue to explore the richness of our sun, advancements like these pave the way for deeper insights into the workings of our universe's very own stellar powerhouse.