We might finally have an explanation for mysterious shadows of falling material in the atmosphere of the Sun, observed during solar flares.
, these mysterious streaks of shadow – referred to as"downward-traveling dark voids" – were thought to be related to the magnetic field interactions that trigger solar eruptions. Now, solar physicists have found that's not actually the case; rather, these"supra-arcade downflows" are the result of fluid interactions in the solar plasma.
Our star is a roiling, turbulent ball of incredibly hot plasma, a fluid made up of charged particles that interacts strongly with electromagnetic forces. Because the Sun is a sphere, the equatorial surface rotates faster than the poles. This results in the solar magnetic field, which in turn can produce strong localized magnetic fields all over the Sun, opening up the sunspots from which flares emerge.
Supra-arcade downflows, embedded in fan-like structures, closely resemble predicted reconnection outflows seen in simulations of magnetohydrodynamics – the movement of electrically conducting fluids. But with one huge problem: they're about 15 percent slower than the simulated outflows, which scientists found difficult to resolve.
Then, they ran simulations of solar flares, and compared these to the observation data. They found that magnetic reconnection is not responsible for the majority of the shadows.Rather, when magnetic reconnection downflows meet the flare's closed loops of magnetic field, they create a termination shock.