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=10

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=<p>Thermal instability (TI) potentially explains the origin of cold gas in the intracluster medium (ICM), which is heated sufficiently by AGN feedback. The H<italic>α</italic> filaments seen in cluster cores provide strong motivation for TI. The hot (<inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mn>7</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula> K) ICM coronae allow the growth of isobaric TI. The multiphase medium (cold-dense—hot-diffuse) forms once TI saturates. However, gravitational stratification can spatially constrain TI, and thermal conduction is known to stabilize all scales below the field length (<italic>λ</italic><sub>F</sub>). In addition, the transport of energy is anisotropic along magnetic fields. Thermal conduction may further trigger gyroscale instabilities and effective reduction of <italic>λ</italic><sub>F</sub>. However, cold gas at small scales <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:mo>&lt;</mml:mo><mml:msub><mml:mrow><mml:mi>λ</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math></inline-formula> needs to be verified in observations. The virial temperature in galactic haloes is lower (<inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula> K) and opens the regime of isochoric TI. In this regime, the cooling time is typically shorter than the 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 mix phases and 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 lower luminosity (similar temperatures). We will discuss the recent progress in TI, its connection to observations, and the analogy to solar prominences.</p>