Cosmological dark matter simulations predict that the central regions of halos have 1/r density cusps. Baryonic processes and dark matter microphysics may resculpt these dark matter cusps, but these process are poorly understood and only weakly constrained by observations of a few low redshift halos.

We have discovered a strong lensing cluster at redshift 1 that includes a bright central image like no other: the central image is resolved! This makes for a uniquely powerful probe of the central regions of a dark matter halo without the need for additional dynamical constraints. An NFW halo cannot reconstruct the data: modelling of our DES imaging with a double powerlaw density profile shows that the central slope must be much shallower than 1/r over at least the central 35 kpc.