| Texto completo | |
| Autor(es): |
Adduci Faria, S.
;
Santos-Lima, R.
;
de Gouveia Dal Pino, E. M.
Número total de Autores: 3
|
| Tipo de documento: | Artigo Científico |
| Fonte: | ASTROPHYSICAL JOURNAL; v. 988, n. 1, p. 20-pg., 2025-07-20. |
| Resumo | |
Galaxy clusters, the largest gravitationally bound structures, host a hot, diffuse plasma with poorly understood viscosity and magnetic field amplification. Astrophysical plasmas are often modeled with magnetohydrodynamics (MHD), but low collision rates in environments such as the intracluster medium (ICM) hinder thermodynamic equilibrium, causing pressure anisotropies and high viscosity. High-beta plasmas, dominated by thermal pressure, are prone to instabilities (e.g., firehose or mirror) that limit anisotropy, reduce viscosity, and enable small-scale dynamo-driven magnetic amplification. This study examines viscosity evolution in the ICM during turbulent magnetic field amplification. We performed 3D MHD simulations of forced turbulence with an initially weak, uniform magnetic field. Using the Chew-Goldberger-Low (CGL)-MHD framework, we incorporate anisotropic pressure dynamics and instability-driven anisotropy limitation. We analyze effective viscosity and dynamo evolution, comparing results with Braginskii-MHD and uniform-viscosity MHD. Our results show that viscosity decreases over time, allowing magnetic field amplification to saturation levels similar to nonviscous MHD. Viscosity distribution becomes bimodal, reflecting (i) collisional values and (ii) turbulence-dominated values proportional to 1 x 10-4LturbUturb in unstable regions. At saturation, 60% of plasma retains collisional viscosity. Braginskii-MHD reproduces similar magnetic amplification and viscosity structures. However, uniform-viscosity MHD, where viscosity equals the mean saturated CGL-MHD value, fails to capture the turbulence inertial range. These findings highlight the need for anisotropic viscosity models in studying ICM processes such as magnetic topology, cosmic ray transport, and active galactic nucleus-driven shocks. Moreover, our CGL-MHD and Braginskii-MHD models match the Coma cluster density fluctuation spectrum, reinforcing its weakly collisional nature. (AU) | |
| Processo FAPESP: | 13/10559-5 - Investigação de fenômenos de altas energias e plasmas astrofísicos: teoria, simulações numéricas, observações e desenvolvimento de instrumentação para o Cherenkov Telescope Array (CTA) |
| Beneficiário: | Elisabete Maria de Gouveia Dal Pino |
| Modalidade de apoio: | Auxílio à Pesquisa - Projetos Especiais |
| Processo FAPESP: | 21/02120-0 - Investigação de fenômenos de astrofísica de plasmas e altas energias, instalação do ASTRI-Mini Array & construção dos telescópios de tamanho pequeno do Cherenkov Telescope Array (CTA-SSTs) |
| Beneficiário: | Elisabete Maria de Gouveia Dal Pino |
| Modalidade de apoio: | Auxílio à Pesquisa - Projetos Especiais |
| Processo FAPESP: | 23/02753-8 - Magnetismo cósmico e propagação do raio cósmico no universo de grande escala |
| Beneficiário: | Stela Adduci Faria |
| Modalidade de apoio: | Bolsas no Brasil - Doutorado Direto |
| Processo FAPESP: | 19/05757-9 - Processos não térmicos em fontes galácticas: modelagens e previsões na iminência do CTA e ASTRI Mini-Array |
| Beneficiário: | Maria Victoria Del Valle |
| Modalidade de apoio: | Auxílio à Pesquisa - Jovens Pesquisadores |
| Processo FAPESP: | 19/04992-4 - Magnetismo cósmico e propagação do raio cósmico no universo de grande escala |
| Beneficiário: | Stela Adduci Faria |
| Modalidade de apoio: | Bolsas no Brasil - Doutorado Direto |