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What are those creepy dark fingers reaching out from solar flares?
It's like Dementors invaded the Sun.
Stars flare all the time. Ours is no exception, but what could previously not be explained were the fingers of darkness reaching out into space from the plasma of a flare. Now they have finally been brought to light as the ghostly spaces between hot plasma, a result of that plasma flowing downward in the turbulence of the Sun. Mismatched substances in that plasma have different densities that force them apart. What you end up seeing are Dementor fingers.
NASA’s floating Solar Dynamics Observatory (SDO) stares at the Sun to find out how solar activity — such as flares, coronal mass ejections, magnetic reconnection — occurs, and how it can possibly mess with Earth. SDO’s Atmospheric Imaging Assembly (AIA) imaged downflows analyzed by a team of researchers, led by Chengcai Shen of the Center for Astrophysics at Harvard & Smithsonian, who recently published their findings in Nature Astronomy.
“These dark downflows are self-organized structures formed in a turbulent interface region below the flare termination shock where the outflows meet the flare arcade, a phenomenon analogous to the formation of similar structures in supernova remnants,” the researchers said.
What they were first suspected to come from was magnetic reconnection. This phenomenon occurs where magnetic field lines break and then come back together in plasma that is extremely electrically conductive (the conductivity of the plasma means it can even form magnetic fields). Magnetic reconnection can cause another weird type of space weather, solar rain, which falls after material condenses in the dips of magnetic fields that are caused by reconnection. Magnetic fields go in every which direction and also cause solar flares.
With magnetic fields being shoved into each other’s faces until they change shape and spew out massive amounts of energy, setting off a solar flare, it was possible that the down flows could have been a product of that. Broken magnetic fields always reconfigure and return to the Sun, so maybe these were just a byproduct. The thought of the dark fingers arising from magnetic reconnection almost made sense, except when it didn’t. Turned out the downflows were too sluggish compared to downflows that are directly caused by magnetic reconnection.
This is where AIA came in. This instrument can image the atmosphere of the Sun in many different wavelengths, and ridiculously fast, so it is able to observe the constant changes going on, from the surface of our star to its scorching insides. The researchers compared those observations to 3D solar flare simulations they created, and found that the fingers were not creeping out from the phenomenon they thought. What are now known as supra-arcade downflows (SADs) were what happened when two fluids with a huge density difference collided.
SADs emerge from a process that is kind of like mixing oil and water, if two types of blistering hot plasma in the Sun’s atmosphere reacted to each other like that. Substances with densities that different just cannot stay together. The density of one fluid (gases and plasmas count as fluids) is much too heavy to remain mixed with the other one for long, so they separate and leave behind gaps where the density is peculiarly low compared to the plasma around them. The dark fingers only look dangerous but may help predict space weather that threatens Earth.
“This interface region hosts a myriad of turbulent flows, electron currents and shocks, crucial for flare energy release and particle acceleration,” the researchers said.
We definitely don’t want that stuff screwing with our satellites, internet, and electrical infrastructures, never mind the intense radiation putting astronauts in harm’s way. These ghosts from the Sun might now be able to tell us what is going on and how we can prevent most of the damage. In a way, they are the opposite of Dementors.