Dark matter, although invisible, makes up most of the universe’s mass and creates its underlying structure. Dark matter’s gravity drives normal matter (gas and dust) to collect and build up into stars and galaxies. Although astronomers cannot see dark matter, they can detect its influence by observing how the gravity of massive galaxy clusters, which contain dark matter, bends and distorts the light of more-distant galaxies located behind the cluster.
As seen in this image, large galaxy clusters contain both dark and normal matter. The immense gravity of all this material warps the space around the cluster, causing the light from objects located behind the cluster to be distorted and magnified. This phenomenon is called gravitational lensing. This sketch shows paths of light from a distant galaxy that is being gravitationally lensed by a foreground cluster.
In 1609, visionary scientist Galileo Galilei turned the newly invented optical device of his day — the telescope — to view the heavens. Almost four centuries later, the launch of NASA’s Hubble Space Telescope aboard the space shuttle Discovery in 1990 started another revolution in astronomy. Developed as a partnership between the United States space program and the European Space Agency, Hubble orbits 340 miles above Earth’s surface.
Image Credit: NASA/ESA
Additional images and information can be found at https://hubblesite.org.