Work

Directly observing the magnetic rope contraction and expansion in space

Year: 2025

Type: article

Abstract: One of the most fundamental hypotheses proposed to explain the electron acceleration in astrophysical and space plasmas is that the magnetic rope can contract and expand during a short period. However, such contraction and expansion of magnetic rope have never been directly evidenced hitherto. Targeting this longstanding problem, here we provide direct evidence for the magnetic rope contraction and expansion by utilizing the first-order Taylor expansion method and the magnetospheric multiscale measurements. The contraction and expansion of magnetic ropes happen during a few seconds in high-speed plasma flows, with the contraction related to an increase of pressure inside the rope and the expansion related to a decrease of pressure. Excitingly, during the magnetic rope contraction we observe electron acceleration, whereas during the magnetic rope expansion we observe electron deceleration. These findings have robustly validated the fundamental hypothesis in astrophysics, i.e., electrons can be accelerated by contracting magnetic ropes. The magnetic flux rope is a crucial structure in astrophysical and space plasmas. Here, the authors show how this structure rapidly contracts/expands and consequently how it accelerates/decelerates electrons, by using an advanced analysis technique.

Source: Nature Communications

DOI: 10.1038/s41467-025-66885-4