For three years, the Hubble Space Telescope spent hundreds of hours peering at distant galaxy clusters and their surrounding areas, looking for the hazy light of the earliest stars in the universe. The mission, known as Frontier Fields, produced dozens of photos of dark backgrounds riddled with galaxies of all shapes, bright jewels so numerous you’d think they were all Photoshopped in.
After 630 hours of observation time, Frontier Fields has come to an end. The mission released its final image Thursday, and it’s no exception. The photo shows Abell 370, one of the six galaxy clusters the program targeted in its observations, and the last to be imaged in such detail. Abell 370 is located 6 billion light-years away in the constellation Cetus, and is home to hundreds of galaxies. Here’s the complete image in all its glory, a combination of optical and infrared measurements:
Not all of the galaxies pictured in this image are actually inside Abell 370. Some of the arcs and streaks of blue and gold light are actually the distorted images of galaxies behind Abell 370. The long, glowing arc in the lower left of the photo, for example, is actually two images of a single spiral galaxy that sits behind the cluster. These objects appear to us this way because of a phenomenon known as gravitational lensing. When light traveling from these distant galaxies reaches Abell 370, the giant cluster’s gravitational pull bends it. The light gets magnified and swings around the cluster, sometimes splitting and going in different directions. When it reaches Hubble, it can look warped and even appear more than once in the same picture.