Mosaic of Gravitationally Lensed Quasars

Each of these Hubble Space Telescope snapshots reveals four distorted images of a background quasar surrounding the central core of a foreground massive galaxy.

The multiple quasar images were produced by the gravity of the foreground galaxy, which is acting 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.

The light rays from each lensed quasar image take a slightly different path through space to reach Earth. The pathway’s length depends on the amount of matter that is distorting space along the line of sight to the quasar. To trace each pathway, the astronomers monitor the flickering of the quasar’s light as its black hole gobbles up material. When the light flickers, each lensed image brightens at a different time. This flickering sequence allows researchers to measure the time delays between each image as the lensed light travels along its path to Earth.

These time-delay measurements helped astronomers calculate how fast the universe is growing, a value called the Hubble constant.

The Hubble images were taken between 2003 and 2004 with the Advanced Camera for Surveys.