Tails of the Unexpected: The Interaction of an Isothermal Shell with a Cloud

TL;DR

This paper introduces a novel hydrodynamical mechanism where a dense shell overruns a cloud, focusing material behind it to form cometary tails, distinct from previous models involving cloud removal or shadowing effects.

Contribution

It presents a new tail formation mechanism through numerical models, applicable to planetary nebulae and superbubble interactions, expanding understanding of astrophysical tail phenomena.

Findings

Shell overrunning causes tail formation behind clouds.

Mechanism differs from cloud removal or shadowing models.

Applicable to planetary nebulae and superbubble interactions.

Abstract

A new mechanism for the formation of cometary tails behind dense clouds or globules is discussed. Numerical hydrodynamical models show that when a dense shell of swept-up matter overruns a cloud, material in the shell is focussed behind the cloud to form a tail. This mode of tail formation is completely distinct from other methods, which involve either the removal of material from the cloud, or shadowing from a strong, nearby source of ionization. This mechanism is relevant to the cometary tails seen in planetary nebulae and to the interaction of superbubble shells with dense clouds.