How do stars form? How large magnetic fields form in the universe? How to predict eruptive space weather events that disrupt cell phone networks and trip power grids?
Results of new research on the solar corona surrounding the sun could help answer these questions, according to a report published by Science Daily.
The US Department of Energy's Princeton Plasma Physics Laboratory experts now have a better understanding on the heating of the atmosphere around the edge of the sun.
This discovery could help experts unravel mysteries such as star formation. It could explain the origin of large-scale magnetic fields in the universe. It may help scientists predict eruptive space weather events that disrupt cell phone networks and blackout power grids on Earth.
Experts at Princeton gathered information on the flow of energy in astrophysical plasmas by simulating the world's largest turbulence.
Princeton University physicist Chuanfei Dong says, “Our direct numerical simulation is the first to provide clear identification of this heating in 3D space.”
The physicist got a better understanding of the heating after conducting 200 million hours of computer time for the world's largest simulation.
Princeton Professor of Astrophysical Sciences Amitava Bhattacharjee, who supervised this research, says, “Chuanfei has carried out the world's largest turbulence simulation. It took over 200 million computer CPUs (central processing units) at the NASA Advanced Supercomputing (NAS) facility.”
Current telescope and spacecraft instruments may not have high enough resolution to identify the process occurring at small scales,” says Dong. The journal Science Advances published his paper on this discovery.
He noted an event called magnetic reconnection that separates and violently reconnects magnetic fields in plasma, the cluster of electrons and atomic nuclei that form the solar atmosphere.
Dong's simulation revealed how rapid reconnection of the magnetic field lines turns the large-scale turbulent energy into small-sale internal energy. So, the turbulent energy efficiently converts to thermal energy at small scales. This superheats the corona.
“Think of putting cream in coffee,” says Dong. “The drops of cream soon become whorls and slender curls. Similarly, magnetic fields form thin sheets of electric current that break up because of magnetic reconnection. This helps the energy cascade from large-scale to small-scale, making the event more efficient in the turbulent solar corona than previously thought.”
When the reconnection is slow while the turbulent cascade is fast, reconnection cannot affect the transfer of energy across scales, he says. When the reconnection rate becomes fast enough to exceed the traditional cascade rate, reconnection can move the cascade toward small scales more efficiently.
It does this by breaking and re-joining the magnetic field lines to create chains of small twisted lines called plasmoids. This changes the understanding of turbulent energy cascade, accepted widely for over half a century.
The new finding ties the energy transfer rate to how fast the plasmoids grow, improving the transfer of energy from large to small scales and strongly heating the corona at these scales.
The discovery shows a regime with an unprecedentedly large magnetic Reynolds number as in the solar corona. The large number characterises the new high-energy transfer rate of the turbulent cascade.
“The higher the magnetic Reynolds number is, the more efficient the reconnection-driven energy transfer is," says Dong.
Current and future spacecraft telescopes could explore the impact of this finding in astrophysical bodies. Unpacking transfer of energy across scales will be important to solving key cosmic mysteries, the research paper says.
(Sudeep Sonawane, an India-based journalist, has worked in five countries in the Middle East and Asia. Email: sudeep.sonawane@gmail.com)
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