Jan. 13 () –
Scientists have taken another step toward understanding how collisionless shock waves, that are found throughout the universe, They are capable of accelerating particles to extreme speeds.
These shock waves are one of nature’s most powerful particle accelerators and have long intrigued scientists for the role they play in the production of cosmic rays, high-energy particles that travel over great distances in the air. space.
The investigation, published in Nature Communicationscombines satellite observations from NASA’s MMS (Magnetospheric Multiscale) and THEMIS/ARTEMIS missions with recent theoretical advances, offering a comprehensive new model to explain electron acceleration in collisionless shock environments.
This research addresses a long-standing enigma in astrophysics: how electrons reach extremely high, or relativistic, energy levels.
For decades, scientists have tried to answer a crucial question in space physics: What processes allow electrons to be accelerated to reach relativistic speeds?
The main mechanism to explain the acceleration of electrons until they reach relativistic energies It is called Fermi acceleration or diffusive shock acceleration (DSA). However, this mechanism requires electrons to be initially energized to a specific threshold energy before they are efficiently accelerated by DSA. Trying to address how electrons achieve this initial energy is known as “the injection problem.”
This new study provides key insights into the electron injection problem, showing that electrons can be accelerated to high energies through the interaction of several processes at multiple scales.
Using real-time data from the MMS mission, which measures the interaction of Earth’s magnetosphere with the solar wind, and the THEMIS/ARTEMIS mission, which studies the upstream plasma environment near the Moon, the research team observed a large-scale, time-dependent (i.e., transient) phenomenon above Earth’s arc shock on December 17, 2017.
During this event, electrons in Earth’s preshock region (an area where the solar wind is preperturbed by its interaction with the arc shock) reached unprecedented energy levels, exceeding 500 keV.
This is a surprising result given that the electrons observed in the preshock region are typically found at energies of about 1 keV, the authors emphasize.
This research suggests that These high-energy electrons were generated by the complex interaction of multiple acceleration mechanismsincluding the interaction of electrons with various plasma waves, transient structures in the preshock, and the Earth’s arc shock.
All of these mechanisms act together to accelerate electrons from low energies of about 1 keV to relativistic energies reaching the observed 500 keV, resulting in a particularly efficient electron acceleration process.
By refining the shock acceleration model, this study provides new insight into the functioning of space plasmas and the fundamental processes that govern energy transfer in the universe.
As a result, the research opens new avenues for understanding the generation of cosmic rays and offers insight into how phenomena within our solar system can guide us. to understand astrophysical processes throughout the universe.
Dr. Sawas Raptis of JHUAPL (Johns Hopkins University Applied Physics Laboratory), lead author of the study, believes that studying phenomena at different scales is crucial to understanding nature. “Most of our research focuses on small-scale effects, such as wave-particle interactions, or large-scale properties, such as the influence of the solar wind,” he said. in a statement.
“However, as we show in this work, by combining phenomena at different scales, we were able to observe their interaction that ultimately energizes particles in space.”
Dr Ahmad Lalti, from Northumbria University and co-author of the research, added: “One of the most effective ways to deepen our understanding of the universe we live in is by using our near-Earth plasma environment as a natural laboratory.
“In this work, we use in situ observation from MMS and THEMIS/ARTEMIS to show how different fundamental plasma processes at different scales work together to energize electrons from low energies to high relativistic energies.
“Such fundamental processes are not limited to our solar system and are expected to occur throughout the universe. This makes our proposed framework relevant to better understand the acceleration of electrons to cosmic ray energies in astrophysical structures light years away from our system.” solar system, as in other star systems, supernova remnants and active galactic nuclei.
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