Fast magnetic explosions. A solar flare can release enough energy in a few minutes to power the entire world for 20,000 years. These solar flares are triggered by an explosive process called magnetic reconnection, and scientists have spent the last half century trying to understand how this process works.
It’s not just a scientific curiosity: a better understanding of magnetic reconnection could provide a better understanding of nuclear fusion and more accurate predictions of particle storms from the Sun that could affect Earth-orbiting technology.
Fast Magnetic Explosions
Now scientists from NASA’s Magnetospheric Multiscale Mission (MMS) think they’ve figured it out. They have developed a theory that explains how the most explosive type of magnetic reconnection, called fast reconnection, occurs and why it occurs at a constant rate. The new theory takes advantage of a common magnetic effect used in everyday devices, such as sensors that synchronize a car’s anti-lock braking system or detect when a cell phone flap is closed.
“We finally understand what makes this type of magnetic reconnection so fast,” said the new study’s lead author, Yi-Hsin Liu, a professor of physics at Dartmouth College in New Hampshire and associate director of the MMS Theory and Modeling Group. “We now have a theory that fully explains this.”
Magnetic reconnection is a process that occurs in plasma, also known as the fourth state of matter. Plasma is formed when a gas receives enough energy to split its atoms, leaving a motley mess of negatively charged electrons and positively charged ions that coexist. This high-energy, liquid-like material is extremely sensitive to magnetic fields.
From solar flares to near-Earth space to black holes, magnetic reconnection occurs everywhere in the universe, rapidly converting magnetic energy into heat and acceleration. Although there are several types of magnetic reconnection, one particularly puzzling variety is known as fast reconnection, which occurs at a predictable rate.
“We’ve known for some time that fast reconnection occurs at a certain rate that seems to be fairly constant,” says Barbara Giles, MMS scientist and researcher at NASA’s Goddard Space Flight Center. “But what really drives that rate has remained a mystery until now.”
The new study, published in an article in Nature’s Communications Physics journal, explains how the rapid reconnection occurs precisely in collisionless plasma, a type of plasma whose particles are so dispersed that individual particles do not collide with each other. When reconnection occurs in space, much of the plasma is in a collision-free state, including plasma from solar flares and space around the Earth.
This theory shows how and why rapid reconnection is likely accelerated by the Hall effect, which describes the interaction between magnetic fields and electric currents. The Hall effect is a common magnetic phenomenon used in everyday technology, such as vehicle wheel speed sensors and 3D printers, where sensors measure speed, proximity, position, or electric currents.
During fast magnetic reconnection, the charged particles in the plasma, namely ions and electrons, stop moving as a group. When the ions and electrons begin to move individually, a Hall effect occurs, creating an unstable energy vacuum in which reconnection occurs. The pressure of the magnetic fields around the energy vacuum causes the vacuum to explode, releasing huge amounts of energy at predictable rates in a very short time.
The new theory will be tested over the next few years. A pyramid-shaped constellation of four space probes will orbit the Earth to study magnetic reconnection in a vacuum-free plasma. In this unique space laboratory, magnetic reconnection can be studied at a higher resolution than is possible on Earth.
“If we understand how magnetic reconnection works, we can better predict events that could affect us on Earth, such as geomagnetic storms and solar flares,” Giles said. “And if we understand how reconnection is triggered, it will also help energy research.