English: Each of these Hubble Space Telescope snapshots reveals four distorted images of a background quasar (an extremely bright region in the center of some distant galaxies) and its host galaxy surrounding the core of a foreground massive galaxy.

The gravity of the massive foreground galaxy acts like a magnifying glass by warping the quasar's light in an effect called gravitational lensing. Quasars are extremely distant cosmic "streetlights" produced by active black holes. Such quadruple images of quasars are rare because of the nearly exact alignment needed between the foreground galaxy and background quasar.

These images come from a study in which astronomers used the gravitational lensing effect to detect the smallest clumps of dark matter ever found. The clumps are located along the telescope's line of sight to the quasars as well as in and around the foreground lensing galaxies.

The presence of the dark matter concentrations alters the apparent brightness and position of each distorted quasar image. Astronomers compared these measurements with predictions of how the quasar images would look without the influence of the dark matter clumps. The researchers used these measurements to calculate the masses of the tiny dark matter concentrations.

Hubble's Wide Field Camera 3 captured the near-infrared light from each quasar and dispersed it into its component colors for study with spectroscopy. The images were taken between 2015 and 2018.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.