File:Galaxy Cluster MACS J0717.5+3745 - 2.jpg

English: At first glance, the scatter of pale dots on this Hubble Space Telescope image looks like a snowstorm in the night sky. But almost every one of these delicate snowflakes is a distant galaxy in the cluster MACS J0717.5+3745, and each is home to billions of stars.

This apparently placid scene also hides a storm of epic scale. This picture shows a region where three galaxy clusters are merging and releasing enormous amounts of energy in the form of X-rays. These distant objects are around 5.4 billion light-years from Earth and were imaged during the Massive Cluster Survey, a project to study distant clusters of galaxies using Hubble.

The amount of mass in this sea of galaxies is huge and is great enough to visibly bend the fabric of spacetime. The strange distortion in the shapes of many of the galaxies, which appear stretched and bent as if they were looked at through a glass bottle, is a result of gravitational lensing, which occurs when the gravitational fields around massive objects bend light around them.

For more information, visit: www.spacetelescope.org/images/potw1017a/

Credit: ESA/Hubble, NASA, and H. Ebeling