Are the heliosphere, very local interstellar medium, and local cavity in pressure balance with Galactic gravity

TL;DR

This study assesses whether the pressures in the heliosphere, local interstellar medium, and Local Cavity are balanced with each other and with Galactic gravity, using in situ spacecraft data and physical models.

Contribution

It provides the first comprehensive pressure survey across the heliosphere and surrounding regions, highlighting the importance of dynamic pressure in maintaining pressure balance.

Findings

Total pressure balance at the heliopause requires significant internal dynamic pressure.

Large dynamic pressure contributions are necessary for pressure balance in the local interstellar medium.

Pressures in the Local Cavity are also influenced by dynamic components.

Abstract

The Voyager spacecraft are providing the first in situ measurements of physical properties in the outer heliosphere beyond the heliopause. These data, together with data from the IBEX and HST spacecraft and physical models consistent with these data, now provide critical measurements of pressures in the heliosphere and surrounding interstellar medium. Using these data, we assemble the first comprehensive survey of total pressures inside and outside of the heliopause, in the interstellar gas surrounding the heliosphere, and in the surrounding Local Cavity to determine whether the total pressures in each region are in balance with each other and with the gravitational pressure exerted by the Galaxy. We inter-compare total pressures in each region that include thermal, non-thermal, plasma, ram, and magnetic pressure components. An important result is the role of dynamic (ram) pressure. Total pressure balance at the heliopause can only be maintained with a substantial contribution of dynamic pressure from inside. Also, total pressure balance between the outer heliosphere and pristine very local ISM (VLISM) and between the pristine VLISM and the Local Cavity requires large dynamic pressure contributions.