MONDian dynamical modeling of NGC 288 with $\beta \neq 0$

TL;DR

This study tests Modified Newtonian Dynamics (MOND) using the low-density globular cluster NGC 288, employing analytical models to fit observed velocity dispersion and brightness profiles, and finds an isotropic solution with specific mass.

Contribution

It provides the first detailed MONDian dynamical modeling of NGC 288 considering anisotropy, using analytical solutions for isothermal spheres with variable anisotropy parameter.

Findings

Optimal fit with isotropic model ($eta=0$)

Estimated total mass of the cluster: $3.5 imes 10^{4} M_{ ext{sun}}$

Supports MOND predictions in low-acceleration regimes

Abstract

NGC 288 is a diffuse Galactic globular cluster, it is remarkable in that its low density results in internal accelerations being below the critical MOND $a_{0}$ acceleration throughout. This makes it an ideal testing ground for MONDian gravity, as the details of the largely unknown transition function between the Newtonian and modified regimes become unimportant. Further, exact analytical solutions exist for isothermal spherical equilibrium structures in MOND, allowing for arbitrary values of the anisotropy parameter, $\beta$. In this paper we use observations of the velocity dispersion profile of NGC 288, which is in fact isothermal, as dynamical constraints on MONDian models for this cluster, where the remaining free parameters are adjusted to fit the observed surface brightness profile. We find the optimal fit requires $\beta =0$, an isotropic solution with a total mass of $3.5 \pm 1.1 \times 10^{4} M_{\odot}$.