Explicarea misterului din spatele reconectarii magnetice rapide

Erupțiile solare și ejecțiile de masă coronară asupra soarelui sunt cauzate de „reconectarea magnetică” – atunci când liniile de câmp magnetic din direcții opuse se îmbină, se unesc și se separă, creând explozii care eliberează cantități uriașe de energie. Credit: NASA Concept Image Lab

Cercetătorii identifică fizica care permite exploziile magnetice rapide în spațiu.

Când liniile de câmp magnetic din direcții opuse se îmbină, ele creează explozii care pot elibera cantități uriașe de energie. Fuziunea liniilor opuse de câmp pe soare creează erupții solare și ejecții de masă coronală, care sunt explozii masive de energie care pot călători pe Pământ în mai puțin de o zi.

În timp ce mecanica generală a reconectarii magnetice este bine înțeleasă, cercetătorii s-au străduit timp de mai bine de jumătate de secol să explice fizica precisă din spatele eliberării rapide de energie care are loc.

Un nou studiu de cercetare de la Dartmouth publicat ieri (28 aprilie 2022) în jurnal Fizica comunicațiilor oferă prima descriere teoretică a modului în care un fenomen cunoscut sub numele de „efectul Hall” determină eficacitatea reconectării magnetice.

Diagrama reconectarii magnetice

Reconectarea magnetică are loc atunci când liniile de câmp magnetic din direcții opuse se îmbină, se unesc și se separă, eliberând cantități masive de energie pentru a încălzi plasmele și a conduce fluxuri de mare viteză. Credit: Yi-Hsin Liu/Dartmouth College

„Viteza cu care liniile câmpului magnetic se reconnectează este de o importanță extremă pentru procesele din spațiu care pot avea impact asupra Pământului”, a declarat Yi-Hsin Liu, profesor asistent de fizică și astronomie în Dartmouth. „După zeci de ani de efort, acum avem o teorie completă pentru a rezolva această problemă de lungă durată”.

Reconectarea magnetică există în natură în plasme, a patra stare a materiei care umple cea mai mare parte a universului vizibil. Reconectarea are loc atunci când liniile de câmp magnetic din direcții opuse sunt atrase unele de altele, se separă, se reunesc și apoi se despart violent.

În cazul unei reconectari magnetice, ruperea liniilor magnetice alungă pe cele magnetizate.[{” attribute=””>plasma at high velocities. The energy is created and displaced to plasmas through a tension force like that which ejects objects from slingshots.

Hall Effect and Magnetic Reconnection

Around the region where reconnection occurs, the departure of the ion motion (blue streamlines in (a)) from the electron motion (red streamlines in (a)) gives rise to the “Hall effect,” which results in the electromagnetic energy transport pattern illustrated by yellow streamlines in (b). This transport pattern limits the energy conversion at the center, enabling fast reconnection. Credit: Yi-Hsin Liu/Dartmouth College

The Dartmouth research focused on the reconnection rate problem, the key component of magnetic reconnection that describes the speed of the action in which magnetic lines converge and pull apart.

Previous research found that the Hall Effect— the interaction between electric currents and the magnetic fields that surround them—creates the conditions for fast magnetic reconnection. But until now researchers were unable to explain the details of how exactly the Hall effect enhances the reconnection rate.

The Dartmouth theoretical study demonstrates that the Hall effect suppresses the conversion of energy from the magnetic field to plasma particles. This limits the amount of pressure at the point where they merge, forcing the magnetic field lines to curve and pinch, resulting in open outflow geometry needed to speed up the reconnection process.

Xiaocan Li, Yi-Hsin Liu, and Shan-Chang Lin

Dartmouth’s Xiaocan Li, postdoctoral researcher (left); Yi-Hsin Liu, Assistant Professor of Physics and Astronomy (center); Shan-Chang Lin, PhD candidate (right). Credit: Robert Gill/Dartmouth College

“This theory addresses the important puzzle of why and how the Hall effect makes reconnection so fast,” said Liu, who serves as deputy lead of the theory and modeling team for NASA’s Magnetospheric Multiscale Mission (MMS). “With this research, we also have explained the explosive magnetic energy release process that is fundamental and ubiquitous in natural plasmas.”

The new theory could further the technical understanding of solar flares and coronal mass ejection events that cause space weather and electrical disturbances on Earth. In addition to using the reconnection rate to estimate the time scales of solar flares, it can also be used to determine the intensity of geomagnetic substorms, and the interaction between the solar wind and Earth’s magnetosphere.

Yi-Hsin Liu

Yi-Hsin Liu, Assistant Professor of Physics and Astronomy, Dartmouth College. Credit: Robert Gill/Dartmouth College

The research team, funded by the National Science Foundation (NSF) and NASA, is working alongside NASA’s Magnetospheric Multiscale Mission to analyze magnetic reconnection in nature. Data from four satellites flying in tight formation around Earth’s magnetosphere as part of the NASA mission will be used to validate the Dartmouth theoretical finding.

“This work demonstrates that fundamental theory insights reinforced by modeling capabilities can advance scientific discovery,” said Vyacheslav Lukin, a program director for plasma physics at NSF. “The technological and societal implications of these results are intriguing as they can help predict impacts of space weather on the electrical grid, develop new energy sources, and explore novel space propulsion technologies.”

The new study can also inform reconnection studies in magnetically confined fusion devices and astrophysical plasmas near neutron stars and black holes. Although there is no current applied use, some researchers have considered the possibility of using magnetic reconnection in spacecraft thrusters.

Reference: “First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas” by Yi-Hsin Liu, Paul Cassak, Xiaocan Li, Michael Hesse, Shan-Chang Lin and Kevin Genestreti, 28 April 2022, Communications Physics.
DOI: 10.1038/s42005-022-00854-x

This work is funded by the NSF’s PHY and AGS Divisions, NASA’s Magnetospheric Multiscale (MMS) mission, and the U.S. Department of Energy.

Co-authors of the study are Paul Cassak, West Virginia University; Xiaocan Li, Dartmouth; Michael Hesse, NASA’s Ames Research Center; Shan-Chang Lin, Dartmouth; and Kevin Genestreti, Southwest Research Institute.

Add Comment