On the interpretation of dark matter self-interactions in Abell 3827

Self-interactions of dark matter (DM) particles can potentially lead to an observable separation between the DM halo and the stars of a galaxy moving through a region of large DM density. Such a separation has recently been observed in a galaxy falling into the core of the galaxy cluster Abell 3827. We estimated the DM self-interaction cross-section needed to reproduce the observed effects and find that the sensitivity of Abell 3827 has been significantly overestimated in a previous study. Our corrected estimate is σ ̃/mDM ~ 3\, cm²\, g⁻¹ when self-interactions result in an effective drag force and σ/mDM ∼ 1.5 cm2 g−1 for the case of contact interactions, in some tension with previous upper bounds.