The arcs of light that ring the center of this Hubble image could easily be mistaken for star trails, glass lens effects, or telescope imperfections. In fact, what we see is not the result of motion of the galaxies, rotation of the telescope, or distortions of light within the telescope. It is actually the mass of an enormous cluster of galaxies—with each individual galaxy made of billions of stars—that behaves like a giant magnifying glass, distorting and amplifying the light of much more distant galaxies behind it.
This effect, known as gravitational lensing, was predicted by Albert Einstein as part of his general theory of relativity. Einstein calculated that starlight should curve as it passes close by massive objects like the Sun. As a result, the positions of the stars appear to shift slightly as the Sun crosses the sky. It was during a total solar eclipse on May 29, 1919 that scientists first successfully tested the theory.
With masses upward of millions of billions times that of the Sun, galaxy clusters like Abell 370 warp space in a much more dramatic way than a single star, magnifying entire galaxies and allowing us to see much deeper into the universe than would otherwise be possible. The power of Hubble combined with nature’s lenses provides the farthest glimpses of our universe, a view that will be extended even farther with the James Webb Space Telescope, scheduled for launch in 2020.