The Tiny Physics Behind Immense Cosmic Eruptions
in fleeting seizures, The sun occasionally throws huge amounts of energy into space. These so-called solar flares last only a few minutes and can trigger catastrophic power outages and blinding auroras on Earth. But our leading mathematical theories of how these flares work cannot predict the strength and speed of what we are observing.
At the heart of these outbursts is a mechanism that converts magnetic energy into powerful bursts of light and particles. This transformation is catalyzed by a process called magnetic reconnection, in which colliding magnetic fields break up and instantly realign, propelling material into the cosmos. In addition to generating energy from solar flares, reconnection could also enable the rapid, high energy particles Ejected by exploding stars, the glow of Jets from feasting black holesand the constant wind Gone by the sun.
Despite the phenomenon’s ubiquity, scientists have struggled to understand how it works so efficiently. A newer theory suggests that minute physics play a big part in solving the mysteries of magnetic reconnection. In particular, it explains why some reconnection events happen so amazingly fast—and why the strongest seem to happen with a characteristic speed. Understanding the microphysical details of reconnection could help researchers create better models of these energetic flares and understand cosmic tantrums.
“So far that’s the best theory I can see,” he said Hantao Ji, a plasma physicist at Princeton University who was not involved in the study. “That’s a great achievement.”
Fumbling with liquids
Almost all known matter in the universe exists in the form of plasma, a fiery gas soup where hellish temperatures have broken down atoms into charged particles. As they fly around, these particles create magnetic fields, which then control the particles’ movements. This chaotic interaction results in a jumble of magnetic field lines that, like rubber bands, store increasing amounts of energy as they are stretched and twisted.
In the 1950s, scientists proposed an explanation for how plasmas release their pent-up energy, a process later called magnetic reconnection. When magnetic field lines directed in opposite directions collide, they can break and cross, launching particles like a double-ended slingshot.
But this idea was more like an abstract painting than a complete mathematical model. Scientists wanted to understand the details of how the process works – the events that affect the snapping, the reason why so much energy is released. But the chaotic interplay of hot gas, charged particles and magnetic fields is difficult to tame mathematically.
The first quantitative theory, described in 1957 by astrophysicists Peter Sweet and Eugene Parker, treats plasmas as magnetized liquids. This suggests that collisions of oppositely charged particles attract magnetic field lines, triggering a runaway chain of reconnection events. Their theory also predicts that this process occurs at a certain rate. Reconnection rates observed in relatively faint laboratory-forged plasmas are consistent with their prediction, as are rates for smaller jets in the lower layers of the Sun’s atmosphere.
But solar flares release energy much faster than Sweet and Parker’s theory can explain. According to their calculations, these eruptions should unfold over months, not minutes.
More recently, NASA observations magnetospheric satellites have found that this faster reconnection occurs even closer to home, in the Earth’s magnetic field. These observations, along with evidence from decades of computer simulations, confirm this “rapid” reconnection rate: In higher-energy plasmas, reconnection occurs at about 10 percent the rate at which magnetic fields propagate — orders of magnitude faster than Sweet and Parker’s theory predicts.
