Understanding the 'feeble giant' Crater II with tidally stretched wave dark matter

The unusually large 'dwarf' galaxy Crater II, with its small velocity dispersion, similar or equal to 3 km s(-1), defies expectations that low-mass galaxies should be small and dense. We combine the latest stellar and velocity dispersion profiles finding Crater II has a prominent dark core of radius similar to 0.71(-0.08)(+0.09) kpc, surrounded by a low density halo, with a transition visible between the core and the halo. We show that this profile matches the distinctive core-halo profile predicted by 'Wave Dark Matter' as a Bose-Einstein condensate, psi DM, where the ground state soliton core is surrounded by a tenuous halo of interfering waves, with a marked density transition predicted between the core and halo. Similar core-halo structure is seen in most dwarf spheroidal galaxies (dSphs), but with smaller cores, similar or equal to 0.25 kpc and higher velocity dispersions, similar or equal to 9 km s(-1), and we argue here that Crater II may have been a typical dSph that has lost most of its halo mass to tidal stripping, so its velocity dispersion is lower by a factor of 3 and the soliton is wider by a factor of 3, following the inverse scaling required by the Uncertainty Principle. This tidal solution for Crater II in the context of psi DM is supported by its small pericenter of similar or equal to 20 kpc established by Gaia, implying significant tidal stripping of Crater II by the Milky Way is expected.

Automated summary

The study finds that Crater II is an unusually large 'dwarf' galaxy with a small velocity dispersion. Its dark matter core is several times the mass of the halo, and there is a visible transition region between the core and the halo. These findings support the prediction of the "Wave Dark Matter" theory that dark matter in galaxies exists in a Bose-Einstein condensed state.