Gravitational Lensing Graphic
This graphic illustrates how a faraway quasar (an extremely bright region in the center of some distant galaxies) is altered by a massive foreground galaxy. The galaxy's powerful gravity warps and magnifies the quasar's light, producing four distorted images of the quasar.
Dark matter is an invisible substance that makes up the bulk of the universe's mass and creates the scaffolding upon which galaxies are built.
Quadruple images of a quasar rare because the background quasar and foreground galaxy require an almost perfect alignment.