A team of solar physicists at NYU Abu Dhabi's Center for Astrophysics and Space Science (CASS) has made significant discoveries about the Sun’s supergranules using data from the Solar Dynamics Observatory.
This research, led by Research Scientist Chris S. Hanson, Ph.D., presents findings that challenge standard theories of solar convection and provide new insights into how heat is transported from the Sun’s interior to its surface.
Breakthrough in Understanding Solar Convection
The Sun generates energy in its core through nuclear fusion, and this energy is transported to the surface, where it escapes as sunlight. The team’s study, titled "Supergranular-scale solar convection not explained by mixing-length theory," was published in the journal Nature Astronomy.
The researchers utilized Doppler, intensity, and magnetic images from the helioseismic and magnetic imager (HMI) onboard 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, a method known as helioseismology, to probe the interior structure of the supergranules. These sound waves, generated by smaller granules, travel through the Sun and can be observed as ripples on the Sun's surface.
By analyzing a large dataset of supergranules, which extend about 20,000 kilometers below the Sun’s surface, the scientists were able to determine the up and down flows associated with supergranular heat transport with unprecedented accuracy.
Discoveries About Supergranules
The team found that the downflows in supergranules appeared approximately 40 percent weaker than the upflows, suggesting the presence of an unseen component in the downflows. Through extensive testing and theoretical arguments, the authors theorize that this "missing" component could consist of small-scale plumes, approximately 100 kilometers in size, that transport cooler plasma down into the Sun’s interior. The sound waves used in helioseismology are too large to detect these small plumes, making the downflows appear weaker than they actually are.
Shravan Hanasoge, Ph.D., research professor and co-author of the paper, explained the significance of these findings: "Supergranules are a significant component of the heat transport mechanisms of the Sun, but they present a serious challenge for scientists to understand. Our findings counter assumptions that are central to the current understanding of solar convection, and should inspire further investigation of the Sun’s supergranules."
Implications for Solar Physics
The discovery that supergranular-scale solarconvection cannot be explained by the widely used mixing-length theory has significant implications for solar physics. The research provides a new perspective on how heat is transported within the Sun and challenges existing models of solar convection. These findings highlight the complexity of the Sun’s internal processes and underscore the need for continued research to fully understand the mechanisms at play.
The study was conducted in collaboration with the Tata Institute of Fundamental Research, Princeton University, and New York University, using NYUAD’s high-performance computing resources. The detailed analysis of supergranules and the use of advanced imaging techniques have provided a deeper understanding of the Sun’s internal structure and the processes that drive solar convection.
Future Research Directions in Solar Physics
This groundbreaking research opens new avenues for studying the Sun’s internal dynamics and improving our understanding of solar convection. The findings suggest that more sophisticated models are needed to accurately represent the heat transport mechanisms within the Sun.
Further investigations into the small-scale plumes and other unseen components could lead to a more comprehensive understanding of the Sun’s behavior and its impact on the solar system.
As solar physicists continue to explore these hidden depths, the knowledge gained from such studies will enhance our ability to predict solar activity and its effects on space weather, which can have significant implications for satellite communications, power grids, and other technologies on Earth.