File:Hubble-ExtendedGrothStrip.jpg

English: Several hundred images taken with NASA's Hubble Space Telescope have been woven together into a rich tapestry of at least 50,000 galaxies, called the Extended Groth Strip. The Hubble view is yielding new clues about the universe's youth, from its "pre-teen" years to young adulthood.

The snowstorm of galaxies in the Hubble panorama does not appear evenly spread out. Some galaxies seem to be grouped together. Others are scattered through space. This uneven distribution of galaxies traces the concentration of dark matter, an invisible web-like structure stretching throughout space. Galaxies form in areas rich in dark matter.

Among the discoveries so far in this galactic tapestry are a giant red galaxy with two black holes at its core; several new gravitational lenses - galaxies whose gravity bends the light from background galaxies into multiple images; and a rogues' gallery of weird galaxies that should keep astronomers busy for a long time trying to explain them.

Hubble's wide view - achieved by weaving together many separate exposures into a mosaic - still only covers a comparatively small slice of sky. The entire width of the image, in angular size, is no bigger on the sky than the apparent width of your finger held at arm's length. To astronomers, however, this seemingly small area is a big piece of celestial real estate.

To cover even this much of the sky, Hubble's Advanced Camera for Surveys snapped more than 500 separate exposures, at 63 different pointings, spread out over the course of one year. The final mosaic is 21 images long by 3 images tall. (The dimensions in degrees are about 1.1 by 0.15 degrees. For comparison, the Moon is about 0.5 degrees in angular size).

The Extended Groth Strip is named for Princeton University physicist Edward Groth. The project is jointly led by Sandra Faber, professor of physics and astronomy at the University of California at Santa Cruz, and Marc Davis, professor of astronomy at the University of California at Berkeley.