Several hundred images taken with NASA’s Hubble Space Telescope have
been woven together into a rich tapestry of at least 50,000 galaxies.
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).

“These images reveal a wealth of galaxies at many stages of their
evolution through cosmic time,” said astronomer Anton Koekemoer of the
Space Telescope Science Institute in Baltimore, Md., who combined all
the Hubble observations to create the final panoramic image, which
contains over 3 billion pixels.

The Hubble observation is part of a larger project to study galaxies in
a moderately small area of sky, which provides a representative sample
of the universe. The study, called the All-wavelength Extended Groth
Strip International Survey (AEGIS), utilized four orbiting telescopes
and four ground-based telescopes. The five-year project involved the
cooperation of more than 50 researchers from around the world observing
the same small region of sky in the radio, infrared, visible,
ultraviolet, and X-ray regions of the electromagnetic spectrum.

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. “The goal was to study the universe as it was when it was
about half as old as it is at present, or about 8 billion years ago, a
time when youthful galaxies undergoing active formation were becoming
quieter mature adults,” said Davis.

The Hubble telescope images reveal a time when galaxies were starting to
reach their mature shapes, looking like the nearby galaxies we see
today. A wide diversity of galaxies can be seen throughout the images.
Some are beautiful spirals or massive elliptical galaxies like those
seen in the nearby universe, but others look like random assemblages of
material, the leftovers from violent mergers of young galaxies. These
resemble some of the most distant, youngest galaxies observed, AEGIS
team members said.

Hubble may have spied tens of thousands of galaxies — many of them odd
and chaotic — but other telescopes observing at wavelengths other than
the visible over wider areas have pinpointed more extreme and exotic
objects, including supermassive black holes and energetic starburst

In a summary paper now posted online in the Astrophysical Journal
Letters, Davis and his colleagues note that AEGIS is providing a unique
combination of deep, intensive observations over a comparatively wide
area, yielding large samples even of rare types of galaxies. They
contrast their work with the Sloan Digital Sky Survey, which has
observed the local universe in great detail, but focuses on only the
last 2 billion years of cosmic evolution. “As of this time, there is no
other region this large on the sky that has been looked at so deeply in
so many different wavelengths,” Faber said.

A total of 19 papers based on the Groth Strip survey will appear in a
special issue of ApJ Letters. All currently are posted online at

AEGIS provides many windows on this time of transition. Ultraviolet and
long-wavelength infrared light from newly born stars, observed by the
GALaxy Evolution eXplorer (GALEX) and the Spitzer Space Telescope,
respectively, shows that stars were being formed at a much higher rate
than today. Shorter-wavelength infrared light measures the total mass of
the stars in each galaxy, allowing astronomers to see how galaxies grow
larger over time, while X-ray and radio observations by the Chandra
X-ray Observatory and the Very Large Array in New Mexico, respectively,
can reveal the presence of powerful black holes at galaxies’ centers.

For images and additional information about the Extended Groth Strip on
the Web, visit

The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. The Space Telescope Science
Institute conducts Hubble science operations. The institute is operated
for NASA by the Association of Universities for Research in Astronomy,
Inc., Washington.