Evidence for Dark Matter Self-Interactions in A3827?

I will discuss the idea of self-interacting dark matter and possible ways to probe such self-interactions in astrophysical systems. In particular, I will focus on the idea that self-interactions can lead to an observable separation between the dark matter halo and the stars of a galaxy moving through a region of large dark matter density. Such a separation has recently been observed in a galaxy falling into the core of the galaxy cluster Abell 3827. I will present an estimate of the DM self-interaction cross section needed to reproduce the observed effects and find some tension with previous upper bounds