October 26, 1998: Astronomers who are using the Hubble telescope to observe the gravitational lensing of light from distant quasars have discovered new evidence about the rate at which the universe is expanding.
The lensing study shows that the universe is expanding at rates slightly slower than, but similar to, rates calculated from the Hubble Key Project to measure the size and age of the universe. The distance scale was one of the primary science problems that Hubble was built to address. In the infrared picture on the left, the light from the quasar PG 1115+080 is split and distorted. In the infrared picture on the right, the four quasar images and the lens galaxy have been subtracted, revealing a nearly complete ring of infrared light. A gravitational lens is created when the gravity of a massive foreground object, such as a galaxy or a black hole, bends the light coming from a far more distant galaxy directly behind it. This "gravitational muscle" focuses the light to give multiple or distorted images of the background object as seen by the observer.See the rest:
Credit: Christopher D. Impey (University of Arizona)