The ring may have been formed when two galactic clusters collided. (discovermagazine.com)
At a NASA press conference today, the astronomers said the ring may have formed one billion to two billion years ago, after a collision between two galactic clusters caused the surrounding dark matter to ripple outward like a stone dropped in water. (scientificamerican.com)
Researchers do not know what dark matter is, but they invoke it to explain why galactic clusters have enough gravity to hold themselves together. (scientificamerican.com)