Two-component model of the interaction of an interstellar cloud with surrounding hot plasma

TL;DR

This paper develops a two-component gasdynamic model to study the interaction between interstellar clouds and hot plasma, estimating cloud lifetimes and X-ray emission due to charge exchange, relevant for understanding local interstellar environments.

Contribution

It introduces a novel two-component model considering charge exchange and heat conduction effects, providing new estimates for cloud lifetimes and X-ray emission in the local interstellar medium.

Findings

Charge exchange X-ray emission can be a significant part of observed X-ray signals.

The model estimates the lifetime of local interstellar clouds, including the one the Sun inhabits.

Charge exchange contributes notably to the X-ray emission at cloud-plasma interfaces.

Abstract

We present a two-component gasdynamic model of an interstellar cloud embedded in a hot plasma. It is assumed that the cloud consists of atomic hydrogen gas, interstellar plasma is quasineutral. Hydrogen atoms and plasma protons interact through a charge exchange process. Magnetic felds and radiative processes are ignored in the model. The influence of heat conduction within plasma on the interaction between a cloud and plasma is studied. We consider the extreme case and assume that hot plasma electrons instantly heat the plasma in the interaction region and that plasma flow can be described as isothermal. Using the two-component model of the interaction of cold neutral cloud and hot plasma, we estimate the lifetime of interstellar clouds. We focus on the clouds typical for the cluster of local interstellar clouds embedded in the hot Local Bubble and give an estimate of the lifetime of the Local interstellar cloud where the Sun currently travels. The charge transfer between highly charged plasma ions and neutral atoms generates X-ray emission. We assume typical abundance of heavy ions for the Local Bubble plasma and estimate the X-ray emissivity due to charge exchange from the interface between cold neutral cloud and hot plasma. Our results show that charge exchange X-ray emission from the neutral-plasma interfaces can be a non-negligible fraction of the observed X-ray emission.