The image of this quasar is split into four by a massive galaxy acting as a gravitational lens. Image credit: Sherry Suyu, European Space Agency/Hubble Space Telescope/NASA
The image of this quasar is split into four by a massive galaxy acting as a gravitational lens. By analyzing slight delays in the light from these lensed quasars, astronomers arrived a new estimate of the Hubble constant — the rate of expansion of the universe. Image credit: Sherry Suyu, European Space Agency/Hubble Space Telescope/NASA