Take a look around the photo. You’re seeing the giant galaxy cluster Abell 2744 better known by its nickname the Pandora Cluster located in the constellation Sculptor. Not only have four separate smaller galaxy clusters piled together over time to merge into one giant one, but the vast amount of mass in Pandora’s Cluster acts like a magnifying glass to coax into view dozens of remote galaxies otherwise hidden in the depths of space.
In the foreground – a relative term, the cluster is 3.5 billion light years away – we see a colorful mix of galaxies with familiar spiral and elliptical forms. All those peculiar blue streaks and arcs are distorted images of galaxies so far away they’re not visible by normal means. The cluster’s powerful gravity acts like a lens, focusing, warping and brightening what would otherwise be lost to view.
According to Einstein, massive objects bend and warp the fabric of space. The more massive the object, the more severe the bending. You can imagine this by picturing a child standing on a trampoline. Her weight depresses the surface to form a little dip or bowl, while a 200-lb. adult creates a much deeper depression in the fabric.
Curved space created by massive objects also bends light rays. Einstein predicted that light from a star passing near the sun would follow this invisible curved landscape and be deflected from an otherwise straight path. Scientists succeeded in measuring the tiny deflection during a total eclipse of the sun in 1919. The bending of light by the power of gravity is called gravitational lensing.
Massive galaxy clusters, which contain regular matter as well as vast quantities of the still-mysterious dark matter that makes up 80% of the material in the universe, act as gravitational lenses. Their powerful gravity magnifies and intensifies the light of galaxies billions of light years in the distance behind them.
That’s exactly what we see happening with the Pandora Cluster. It’s the first of six galaxy clusters in the three-year-long Frontier Fields program that will be employed as deep space probes to yield our deepest views of the Universe to date using gravity as a lens.
The new Hubble images are expected to reveal galaxies some 10-100 times fainter than any previously observed. Measuring the degree and direction of the tortured shapes of the background lensed galaxies will also help astronomers nail down how much dark matter lurks in the six clusters. Go Hubble go!
For more on gravitational lensing, check out this Hubblecast on the topic.