Have you ever looked through a wine glass and noticed objects farther away appear distorted? This effect, caused by the bending of light as it passes through the curved surface, is somewhat similar to strong gravitational lensing; like the wine glass warping light from distant objects, a foreground galaxy warps the appearance of a galaxy behind it by magnifying it, distorting it into arcs, and/or creating multiple images of it [Figure 2]. In my research, I use machine learning and data from the Dark Energy Spectroscopic Instrument (DESI) to look for a specific type of gravitational lens: a quasar lensing a background galaxy. But I want to learn about the lens itself, not the galaxy behind it.

Two powerful probes of dark matter on small scales—strong gravitational lensing and ultra-faint dwarf galaxies—join together to set world-leading constraints on the nature of the dark matter particle in a recent study led by KIPAC researchers, including the authors. In the process, we have shown that combining these probes provides a framework to detect “dark halos,” clumps of dark matter that have no associated visible light, using the vast amounts of deeper data promised by upcoming surveys.