Are Milky-Way dwarf-spheroidal galaxies dark-matter free?

TL;DR

This paper argues that the high velocity dispersions observed in Milky Way dwarf spheroidal galaxies can be explained by tidal shocks rather than dark matter, challenging the conventional dark matter paradigm for these galaxies.

Contribution

It demonstrates that dark-matter free dwarf spheroidal galaxies in non-equilibrium can reproduce observed scaling relations, questioning the necessity of dark matter in these systems.

Findings

Tidal shocks explain high velocity dispersions without dark matter.

Dark-matter free models fit observed scaling relations.

Dwarf spheroidals likely originate from tiny dwarf irregular galaxies.

Abstract

We have found that the high velocity dispersions of dwarf spheroidal galaxies (dSphs) can be well explained by Milky Way (MW) tidal shocks, which reproduce precisely the gravitational acceleration previously attributed to dark matter (DM). Here we summarize the main results of Hammer et al. (2019) who studied the main scaling relations of dSphs and show how dark-matter free galaxies in departure from equilibrium reproduce them well, while they appear to be challenging for the DM model. These results are consistent with our most recent knowledge about dSph past histories, including their orbits, their past star formation history and their progenitors, which are likely tiny dwarf irregular galaxies.