(by Luis Padron)
Our Sun is a main sequence star which actively fuses hydrogen into helium in its core. In certain regions of the Sun, the energy created by the hydrogen “burning” is carried to its surface by convection. However, intense magnetic fields in sunspots strangle the normal up-flow of energy from the interior, so energy is unable to reach the surface in these areas leaving the sunspot cooler and therefore darker than its surroundings. The strong magnetic fields in these convection zones promote cooling, thus the hot gas near the Sun’s surface contracts and sinks at speeds of up to 4,000 kilometers per hour. This drives an inward flow, like a planet-sized whirlpool. Of course, seeing behind the scenes in sunspots is not easy; the Sun below the photosphere is opaque and hidden. The only way to investigate the morphology and the structure of sunspots is through helioseismology. Using the Helioseismic and Magnetic Imager (HMI) on SDO, we can explore the solar interior by detecting natural sound waves on the Sun’s surface.
For more information:
- Detection of Emerging Sunspot Regions
- Local Helioseismology of Sunspots
- The Exploratorium’s Guide to Sunspots
- Sunspots and Solar Storms
Image Credit: NASA/SOHO/MDI/Alexander Kosovichev/Tom Bridgman