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The Hubble Ultra Deep Field (HUDF) is one of the deepest visible-light images of the cosmos. In this view, released in March 2004, Hubble looked back in time, through a "core sample" of the universe, revealing galaxies at many stages of evolution. Since the light from these distant galaxies must travel for billions of years before arriving at Earth, we are seeing the galaxies as they appeared when the light left them, billions of years ago.
The snapshot includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies may be among the most distant known, existing when the universe was just 800 million years old. The nearest galaxies — the larger, brighter, well-defined spirals and ellipticals — thrived about 1 billion years ago, when the cosmos was about 13 billion years old.
In contrast to the spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. These oddball galaxies are portraits from a period when the universe was younger and more chaotic.
In this image, blue and green correspond to colors that can be seen by the human eye, such as hot, young, blue stars and the glow of Sun-like stars in the disks of galaxies. Red represents near-infrared light, which is invisible to the human eye, such as the red glow of dust-enshrouded galaxies.