# Ghostly Galaxies as Solitons of Bose-Einstein Dark Matter

## TL;DR

This paper proposes that dwarf galaxies with large dark cores, like Antlia II, can be explained by dark matter as ultra-light boson condensates forming stable solitons, aligning with observations and quantum principles.

## Contribution

It introduces a model where dwarf galaxy cores are stable solitons of Bose-Einstein condensate dark matter, explaining their size and density with an ultra-light boson mass.

## Key findings

- Antlia II's large, low-density core fits the soliton model of Bose-Einstein condensate dark matter.
- An ultra-light boson of ~1.1×10⁻²² eV explains the galaxy's properties.
- The model predicts a lower limit on galaxy size set by quantum uncertainty.

## Abstract

The large dark cores of common dwarf galaxies are unexplained by the standard heavy particle interpretation of dark matter. This puzzle is exacerbated by the discovery of a very large but barely visible, dark matter dominated galaxy Antlia II orbiting the Milky Way, uncovered by tracking star motions with the {\t Gaia} satellite. Although Antlia II has a low mass, its visible radius is more than double any known dwarf galaxy, with an unprecedentedly low density core. We show that Antlia II favors dark matter as a Bose-Einstein condensate, for which the ground state is a stable soliton with a core radius given by the de Broglie wavelength. The lower the galaxy mass, the larger the de Broglie wavelength, so the least massive galaxies should have the widest soliton cores of lowest density. An ultra-light boson of $m_\psi \sim 1.1 \times10^{-22}$ eV, accounts well for the large size and slowly moving stars within Antlia II, and agrees with boson mass estimates derived from the denser cores of more massive dwarf galaxies. For this very light boson, Antlia II is close to the lower limiting Jeans scale for galaxy formation permitted by the Uncertainty Principle, so other examples are expected but none significantly larger in size. This simple explanation for the puzzling dark cores of dwarf galaxies implies dark matter as an ultra-light boson, such as an axion generic in String Theory.