Scientists at NASA have developed a theory that explains how explosions occur on the Sun and help better predict geomagnetic storms and solar flares that can impact Earth.
An explosive process called magnetic reconnection triggers solar flares, which can, in just minutes, release enough energy to power the whole world for 20,000 years. Scientists have spent the last half-century trying to understand how this process happens.
The team at NASA's Magnetospheric Multiscale Mission (MMS) has a new theory that explains how the most explosive type of magnetic reconnection - called fast reconnection - occurs and why it happens at a consistent speed. Magnetic reconnection is a process that occurs in plasma - energetic, fluid-like material that is exquisitely sensitive to magnetic fields.
From flares on the Sun to near-Earth space, to black holes, plasmas throughout the universe undergo magnetic reconnection, which rapidly converts magnetic energy into heat and acceleration. While there are several types of magnetic reconnection, one particularly puzzling variant is known as fast reconnection, which occurs at a predictable rate.
"We have known for a while that fast reconnection happens at a certain rate that seems to be pretty constant," said Barbara Giles, project scientist for MMS and research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "But what really drives that rate has been a mystery, until now."
The new research, published in a paper in Nature's Communications Physics journal, explained how fast reconnection occurs specifically in collisionless plasmas - a type of plasma whose particles are spread out enough that the individual particles don't collide with one another. Where reconnection happens in space, most plasma is in this collisionless state, including the plasma in solar flares and the space around Earth.
The team showed the theory using a common magnetic effect called the Hall effect - a common magnetic phenomenon that's used in everyday technology, like vehicle wheel speed sensors and 3D printers, where sensors measure speed, proximity, positioning, or electrical currents.
During fast magnetic reconnection, charged particles in a plasma - namely ions and electrons - stop moving as a group. As the ions and electrons begin moving separately, they give rise to the Hall effect, creating an unstable energy vacuum where reconnection happens.
Pressure from the magnetic fields around the energy vacuum causes the vacuum to implode, which quickly releases immense amounts of energy at a predictable rate.
"Ultimately, if we can understand how magnetic reconnection operates, then we can better predict events that can impact us on Earth, like geomagnetic storms and solar flares, Giles said. "And if we can understand how reconnection is initiated, it will also help energy research because researchers could better control magnetic fields in fusion devices."
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