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arXiv · 2609.07793

Two-Phase Structure of Synchrotron-Cooling-Unstable Relativistic Plasma

Agnieszka Wierzchucka·Pablo J. Bilbao·Robert J. Ewart·Dmitri A. Uzdensky·Alexander A. Schekochihin
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Abstract

Using analytic theory, radiative particle-in-cell (PIC) simulations, and fluid simulations, we show that relativistic, synchrotron-cooling, collisionless, high-$\beta$ pair plasmas filament into a two-phase medium. This process occurs through the interplay of the synchrotron cooling instability (SCI) with the synchrotron firehose instability (SFHI). One phase has high plasma~$\beta$ and is infested with small-scale firehose fluctuations, which scatter particles and pin the pressure anisotropy to the firehose-marginal level. The other phase has much lower~$\beta$, causing the suppression of firehose modes and thus allowing large pressure anisotropies. We propose a fluid model for this two-phase plasma, which we use to study the linear and nonlinear evolution of the SCI and SFHI, and to predict the emergence time of the two-phase structure.

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Agnieszka Wierzchucka, Pablo J. Bilbao, Robert J. Ewart, Dmitri A. Uzdensky, Alexander A. Schekochihin. 2026-09-07. Two-Phase Structure of Synchrotron-Cooling-Unstable Relativistic Plasma. https://arxiv.org/abs/2609.07793

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