Tiny Solar Whirlpools May Hold the Secret to the Sun’s Blistering Corona

For the second time in a few weeks, we’re writing about research into the temperature gap between the Sun’s surface and its corona. More and more data from various missions continue to feed this wave of discovery. A new paper by Katariina Nykyri of Embry-Riddle, recently published in The Astrophysical Journal Letters, adds to this growing body of work. She argues that millions of tiny whirlpools scattered across the Sun’s surface could be the energetic engine driving that temperature difference. Earlier this year, the Daniel K. Inouye Solar Telescope (DKIST), located atop Haleakalā on Maui, took extremely high resolution images of the Sun’s surface. For the first time, scientists could make out whirlpools of plasma, a few dozen kilometers across, dotted around the Sun’s surface. When this research was published in August, Dr. Nykyri had a bit of a “Eureka!” moment, according to a press release from the University. Her research had focused on Kelvin-Helmholtz waves. On Earth, these are most commonly seen in broken ocean swells or ripple-pattern clouds. However, they are also present elsewhere in the solar system, driving gas patterns on Jupiter. On the Sun, they occur when fast-moving plasma passes slower, magnetized plasma. They contain an absurd amount of mechanical energy. The vortices created by these waves are the very structures DKIST resolved on our star’s surface. As these vortices churn across the solar surface, their vast kinetic energy transfers into the Sun's magnetic fields, converting mechanical motion into magnetic stress. Fraser talks about the features of the Sun that we are only now getting a glimpse of thanks to new technologies. Dr. Nykyri set out to answer how much energy these vortices carry and whether it equals the total energy needed to heat the corona. After accounting for the velocity shear, density difference, and vertical heights of the tornadoes, she reached a conclusion. On average, each vortex contains around two septillion ergs—a unit of energy commonly used in solar physics. Across the Sun’s 1.4-million-kilometer surface, millions of these vortices spin up and dissipate every few minutes. When these vortices dissipate, their energy must go somewhere. According to Dr. Nykyri, it appears to enter the corona through magnetic reconnection. Solar physicists have long thought this process plays a key role in coronal heating. As each KH vortex spins, it squeezes nearby magnetic field lines together. This forms ultra-thin current lines ranging from a few centimeters to meters across. Once they’re squeezed past a certain point, they start to violently snap and rearrange. That is the process of magnetic reconnection, and it converts the stored magnetic energy into heat and high-speed plasma jets that are fundamental components of the solar corona. In other words, the KH vortices are the driving force behind the process of reconnection of the Sun’s magnetic field lines. Frase talks about how hot the Sun actually is. When the energy they store is released, it has to have somewhere to go, though. And these vortices don’t always cause reconnections only in the corona - they also do so on the surface. So why does the corona seem so much hotter? Particle density. When a magnetic line snaps on the surface, the energy is immediately distributed between trillions of neutral atoms. Each atom’s temperature is commensurately raised, but only by a tiny amount. In the corona, though, atoms are much less plentiful, but the same amount of energy is released. So each magnetic snap increases the temperature of an individual atom by much more in the corona than down on the surface. According to the paper, only five to eight percent of the mechanical energy stored in the vortices needs to make the journey upward to the corona to replenish the heat that is otherwise radiated away. Even in darker “coronal holes”, a max of 21% of the energy from the vortices would be capable of maintaining the temperature of the corona. This work is a major step toward understanding the heating process, but more research is needed. Scientists still must track wave transmission and polarization through the chromosphere. This will confirm whether as much energy reaches the Sun’s chromosphere as Dr. Nykyri suggests is necessary to maintain coronal temperatures. If her theory holds, some of the high temperatures on our star will be proven to stem from relatively small plasma tornadoes floating across its surface. Learn More: Embry-Riddle - Embry‑Riddle Researcher Helps Solve Mystery Around Heating of Sun’s Corona K. Nykyri - Photospheric Kelvin–Helmholtz Vortices as Possible Drivers of Coronal Heating: Implications of the DKIST Observations UT - Solar Orbiter Traces Giant Magnetic Switchbacks Directly Back to the Sun UT - Cluster Spacecraft Catch a Magnetic Reconnection