In just minutes, a flare on the Sun can release enough energy to power the whole world for 20,000 years. An explosive process called magnetic reconnection triggers these solar flares and scientists have spent the last half-century trying to understand how the process happens.
It’s not just a scientific curiosity: A
fuller understanding of magnetic reconnection could enable insights into
nuclear fusion and provide better predictions of particle storms from the Sun
that can affect Earth-orbiting technology.
Now, scientists with NASA’s Magnetospheric
Multiscale Mission, or MMS, think they’ve figured it out. The scientists have
developed a theory that explains how the most explosive type of magnetic
reconnection – called fast reconnection – occurs and why it happens at a
consistent speed. The new theory uses a common magnetic effect that’s used in
household devices, such as sensors that time vehicle anti-lock braking systems
and know when a cell phone flip cover is closed.
“We finally understand what makes this
type of magnetic reconnection so fast,” said lead author on the new study
Yi-Hsin Liu, a physics professor at Dartmouth College in New Hampshire and the
deputy-lead of MMS’ theory and modeling team. “We now have a theory to explain
it fully.”
Magnetic reconnection is a process that
occurs in plasma, sometimes called the fourth state of matter. Plasma forms
when a gas has been energized enough to break apart its atoms, leaving a motley
of negatively charged electrons and positively charged ions existing
side-by-side. This energetic, fluid-like material 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 and funded in part by the National Science Foundation, explains 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 new theory shows how and why fast
reconnection is likely sped up by the Hall effect, which describes the
interaction between magnetic fields and electric currents. The Hall effect is 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.
This visualization shows the Hall effect, which occurs when the motion of the heavier ions (blue) decouple from the lighter electrons (red) as they enter the region with strong electric currents (golden region). Credits: Tom Bridgman/NASA's Scientific Visualization Studio
The new theory will be tested in the coming years with MMS, which uses four
spacecraft flown around Earth in a pyramid formation to study magnetic
reconnection in collisionless plasmas. In this unique space laboratory, MMS can
study magnetic reconnection at a higher resolution than would be possible on
Earth.
“Ultimately, if we can understand how magnetic reconnection operates, then
we can better predict events that can impact us at 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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By Mara
Johnson-Groh
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Source: NASA’s MMS Mission Cracks 60-Year-Old ‘Explosive’ Magnetic
Mystery | NASA
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