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), led by research scientist Chris S. Hanson, Ph.D., has discovered the internal structure of the sun’s supergranules, a fluid structure that transports heat from the sun’s hidden interior to its surface. The researchers’ analysis of the supergranules presents a challenge to the current understanding of solar convection.

The Sun generates energy at its core through nuclear fusion; that energy is then transported to the surface, where it emerges as sunlight. In a study titled “Supergranular-scale solar convection not explained by mixing length theory,” published in the journal Astronomy of Natureresearchers explain how they used Doppler, intensity, and magnetic images from the Helioseismic and Magnetic Imager (HMI) aboard NASA’s Solar Dynamics Observatory (SDO) satellite to identify and characterize approximately 23,000 supergranules.

Since the sun’s surface is opaque to light, the NYUAD scientists used sound waves to probe the internal structure of the supergranules. These sound waves, which are generated by smaller granules and are ubiquitous in the sun, have been used successfully in the past in a field known as helioseismology.

By analyzing such a large data set of supergranules, which were estimated to extend 20,000 km (~3% inland) below the sun’s surface, the scientists were able to determine the up and down fluxes associated with supergranular heat transport with unprecedented precision. . In addition to establishing how deep the supergranules extend, the scientists also found that the downflows appeared roughly 40% weaker than the upflows, suggesting that some components were missing from the downflows.

Through extensive tests and theoretical arguments, the authors theorize that the “missing” or invisible component may consist of small-scale (approximately 100 km) plumes that transport cooler plasma down into the solar interior. Sound waves on the Sun would be too large to sense these plumes, making the outflows appear fainter. These findings cannot be explained by the widely used description of the mixing length of solar convection.

“Supergranules are an important component of the sun’s heat transport mechanisms, but they pose a serious challenge for scientists to understand,” said Shravan Hanasoge, Ph.D., research professor, co-author of the paper and co-principal investigator. of CASS. “Our findings challenge assumptions that are fundamental to the current understanding of solar convection and should inspire further investigations of solar supergranules.”

The research was conducted within CASS at NYUAD in collaboration with the Tata Institute of Fundamental Research, Princeton University and New York University, using NYUAD’s high-performance computing resources.