A Soliton Solution for the Central Dark Masses in 47- Tuc Globular Cluster and Implications for the Axiverse

TL;DR

This paper proposes that a solitonic core of light bosonic dark matter explains the rising stellar proper motions at the center of 47-Tuc, challenging the black hole hypothesis and supporting the existence of multiple light axion-like particles.

Contribution

It introduces a solitonic dark matter core as an alternative to black holes for the central mass in 47-Tuc, linking it to axion physics and string theory predictions.

Findings

A solitonic dark matter core can account for the observed stellar motions.

The core size is consistent with light bosons of mass ≥ 10^{-18} eV.

Supports the existence of multiple light axion-like particles.

Abstract

We offer a standing wave explanation for the rising proper motions of stars at the center of the globular cluster 47-Tucanae, amounting to $\simeq 0.44\%$ of the total mass. We show this can be explained as a solitonic core of dark matter composed of light bosons, $ m \geq 10^{-18} eV $, corresponding to $ \leq 0.27 pc$, as an alternative to a single black hole (BH) or a concentration of stellar BH remnants proposed recently. This is particularly important as having a concentrated stellar BH remnant with the above radii is very challenging without the heavy core since the three body encounters would prevent the BHs to be that concentrated. We propose this core develops from dark matter captured in the deep gravitational potential of this globular cluster as it orbits the dark halo of our galaxy. This boson may be evidence for a second light axion, additional to a lighter boson of $10^{-22} eV$, favored for the dominant dark matter implied by the large dark cores of dwarf spheroidal galaxies. The identification of two such light bosonic mass scales favors the generic string theory prediction of a wide, discrete mass spectrum of axionic scalar fields.