2000ApJ...542L...1S

Observations of a flat-density profile in the cores of dark matter-dominated halos on the two extremes of mass for virialized objects in the universe, dwarf galaxies and galaxy clusters, present a serious challenge to the current standard theory of structure formation involving cold dark matter (CDM). By contrast, N-body simulations of halo formation in the latter indicate density profiles that are singular and steeply rising toward the center. A flat-density core on the cluster scale is indicated by gravitational lensing observations, most significantly by the strong-lensing measurements of Cl 0024+1654 by the Hubble Space Telescope. A recent reanalysis of this cluster has suggested that a uniform-density core is not demanded by the data, thereby eliminating a significant piece of the conflict between the observations and the CDM theoretical predictions. We show here, however, that the singular mass profile that that analysis reports as consistent with the lensing measurements of Cl 0024+1654 implies a velocity dispersion that is much higher than the measured value for this cluster.