ocr: GALAXY CLUSTERS Extending backward billlions of light-years from the Milky Way, massive galaxy clusters act as lenses allowing astronomers tosee even further back to - the time when galaxies first formed. Below is an image of Abell 2218, a massive galaxy cluster exhibiting gravitational lensing. A more distant galaxy is seen as arcs of light surrounding the cluster. CREDIT: NASA, A. Fruchter (STSCI) and the ERO Team (STScI/ST-ECF).
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