This illustration separates the XDF into three planes showing foreground, background, and very far background galaxies. These divisions reflect different epochs in the evolving universe. Fully mature galaxies are in the foreground plane that shows galaxies as they looked less than 5 billion years ago. The universe is rich in evolving, nearly mature galaxies from 5 to 9 billion years ago. Beyond 9 billion years the universe is awash in compact galaxies and proto-galaxies, blazing with young stars.