Preliminary Study on Dark Matter-Dominated Systems: Further Analysis for galactic dark matter halos with Pressure

TL;DR

This study explores the properties of dark matter halos modeled as perfect fluids with pressure, analyzing their stability and implications for galactic rotation curves, and finds that such static, spherically symmetric configurations are unstable.

Contribution

It introduces a detailed analysis of dark matter halos with pressure based on the universal rotation velocity profile, revealing their instability and challenging static, spherical models.

Findings

Dark matter halos modeled as perfect fluids are unstable under the studied conditions.

The universal rotation velocity profile cannot be explained by static, spherically symmetric dark matter halos with pressure.

Halos are likely non-spherical, dynamic, or not in hydrostatic equilibrium.

Abstract

Low surface brightness galaxies are an excellent laboratory where stars and baryonic matter act as tracers of the gravitational potential of the dark matter halo. If dark matter is modeled as a perfect fluid, then spherically symmetric and static dark matter halos in hydrostatic equilibrium demand that dark matter should have an intrinsic pressure that counteracts the gravitational attraction that the dark matter halo exerts on itself. This static fluid (dark matter-dominated system, where the presence of baryons is negligible) has a specific equation of state for each rotational velocity profile of the stars in galaxies. In this work, we study the dark matter equation of state needed for the self-gravitating object to produce a gravitational potential such that the tracers follow the Universal Rotational Velocity Profile for stars of spiral galaxies proposed by Persic et al. (1996) and analyze the properties of the self-gravitating structures that emerge from this equation of state.The resulting configurations explaining the observed rotational speeds are found to be unstable. We conclude that the halo is not in hydrostatic equilibrium, it is nonspherically symmetric, or it is not static if the universal velocity profile should be valid for fitting the rotational velocity curve of the galaxies.