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“Astronomers using NASA’s Hubble Space Telescope have found a puzzling arc of light behind an extremely massive cluster of galaxies residing 10 billion light-years away. The galactic grouping, discovered by NASA’s Spitzer Space Telescope, was observed as it existed when the universe was roughly a quarter of its current age of 13.7 billion years.

The giant arc is the stretched shape of a more distant star-forming galaxy whose light is distorted by the monster cluster’s powerful gravity, an effect called gravitational lensing. The “lensed” galaxy existed 10 billion to 13 billion years ago.

The cluster is the most massive found at that epoch, weighing as much as 500 trillion suns. The assemblage is 5 to 10 times larger than other clusters found at such an early time in the universe’s history. This unique system constitutes the most distant cluster known to “host” a giant gravitationally lensed arc.

The giant arc is the stretched shape of a more distant galaxy whose light is distorted by the monster cluster’s powerful gravity, an effect called gravitational lensing. The trouble is, the arc shouldn’t exist.