This composite image from the Hubble Space Telescope’s Advanced Camera for Surveys and its Wide Field Camera 3 shows a huge cluster of galaxies some six billion light years away known as PSZ23 G138.61-10.84. The image is from an observing programme called the Reionization Lensing Cluster Survey, or RELICS. The RELICS project has studied 41 galaxy clusters to help locate the brightest distant galaxies for follow-on observations by the James Webb Space Telescope, scheduled for launch in 2020.
Astronomers using data from the NASA/ESA Hubble Space Telescope and other observatories have performed an accurate census of the number of galaxies in the universe. The researchers came to the surprising conclusion that the observable universe contains at least two trillion galaxies. The results also help solve an ancient astronomical paradox — why is the sky dark at night?