AUTHOR=Choudhury Prakriti Pal 

TITLE=Formation of multiphase plasma in galactic haloes and an analogy to solar plasma

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2023.1155865

DOI=10.3389/fspas.2023.1155865

ISSN=2296-987X

ABSTRACT=Thermal instability (TI) potentially explains the origin of cold gas in the intracluster medium (ICM), which is heated sufficiently by AGN feedback. The H$\alpha$ filaments seen in cluster cores provide strong motivation for TI. The hot ($\sim 10^7$ K) ICM coronae allows the growth of isobaric TI. Multiphase medium (cold-dense — hot-diffuse) forms once TI saturates. However, gravitational stratification can spatially constrain TI, and {\color{red} thermal conduction is known to stabilize all scales below the Field length ($\lambda_{\rm F}$). In addition, the transport of energy is anisotropic along magnetic fields. Thermal conduction may further trigger gyro-scale instabilities and effective reduction of $\lambda_{\rm F}$. But cold gas at small scales ($< \lambda_{\rm F}$) needs to be verified in observations. The virial temperature in galactic haloes is lower ($\sim 10^6$ K) and opens the regime of isochoric TI}. In this regime, cooling time is typically shorter than sound-crossing time, and large-scale isochoric clouds are rendered unstable. The linear and non-linear isochoric clouds have interesting differences which potentially lead to either fragmentation of the cloud or not. On saturation, TI produces a turbulent medium that helps to mix phases, thermalize kinetic energy, and thus completes a cycle of condensation and heating. Various aspects of condensation, stratified turbulence, and magnetized transport are physically identical in solar coronae but scaled down to {\color{red} lower luminosity (similar temperatures)}. We will discuss the recent progress in TI, its connection to observations, and the analogy to solar prominences.