Galaxy Clusters (image) University of Copenhagen Caption Researchers have analyzed measurements of the light from galaxies in approximately 8,000 galaxy clusters. Galaxy clusters are accumulations of thousands of galaxies (every light in the image is a galaxy), which are held together by their own gravity. This gravity affects the light that is sent out into space from the galaxies. Credit Hubble Space Telescope Usage Restrictions Hubble Space Telescope Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.