Gravitational Lensing as a Probe of Cold Dark Matter Subhalos

Figure 7

A galaxy with a dark matter halo produces distinct macroimages of a background light source. If this source displays intrinsic variability, observable time delays between the different macroimages may occur. If one of the macroimages experiences further small-scale image splitting due to a subhalo along the line of sight, a light echo may be observable in the affected macroimage. This may serve as a signature of millilensing in cases where the small-scale images blend into one due to insufficient angular resolution of the observations.