The Extended Groth Strip is the skinny box at upper right off the handle of the Big Dipper. The middle panel shows the full strip, a small portion of which is enlarged at right. Credit: NASA/ESA/ M. Davis
Another snowstorm will soon bear down on my town, the third in two weeks. While blizzards and gales are wonderful phenomena, many of us are ready for sunshine and flowers. A snowstorm of a different sort sends photons of light our way every clear spring night. From high over head in the constellation of the Great Bear 50,000 galaxies hidden in a tiny box of sky tell us about the universe’s pre-teen to early adult years.
The Extended Groth Strip is only about 1 degree long or the wide of two side-by-side full moons yet it contains over 50,000 galaxies. Click to see a full-sized version. Credit: NASA/ESA
Astronomers used the Hubble Space telescope between June 2004 and March 2005 to make over 500 separate exposures during 63 separate pointings of a narrow sliver of sky 1.1 degrees long by 0.15 degrees wide or about the width of the very tip of your little finger held at arm’s length against the sky. They chose the Big Dipper area because there’s little cosmic dust and few intervening Milky Way stars in that region to block the view of deepest space.
The box, called the Extended Groth Strip, after Princeton University physicist Edward Groth, contains far more galaxies than even the famed Hubble Ultra-Deep Field (approx. 10,000 galaxies) and Extreme Deep Field (15,000 galaxies) images. Click HERE to see a monster version of Groth and sample some of these galaxies for yourself.
A small, cropped portion of the full strip shows several stars (at left). Just about every other tiny blip you see is a galaxy. Credit: NASA/ESA
Whenever we cast our gaze at the starry sky, we look back in time. Since most naked eye stars are within a few hundred light years of Earth, the light we see left them decades to centuries ago giving us a picture of them as they were. Since stars have lifetimes measured in the hundreds of millions to billions of years, all the stars we see tonight are undoubtedly still there and look much the same if we could see them in “real time.”
A selection of normal galaxies from the Groth Strip similar to those we see in the current era dominated by a concentration of stars in center called the “bulge” and surrounded by a flattened disk of stars. Click to enlarge and learn more. Credit: NASA/ESA
This doesn’t hold true when we use a telescope like Hubble, which can see far more deeply into space and sample the billions-year-old light of the most remote galaxies. Recording the light of a galaxy 8 billion light years away we see it as it was 8 billion light years ago.
Many galaxies from that earlier era are small, blue and hot with new star formation. If we could see them “now”, they would appear redder. Much of the gas available during that great burst of star-making would be processed and enriched with new elements created by earlier generations of stars.
Some of the more distant (hence younger) oddball galaxies photographed in the Strip by the Hubble scope. Top row: Elliptical galaxies bending the light objects in the more distant background into blue arcs; center row: small galaxies in the process of merging; bottom row: galaxies with irregular, clumpy shapes with blue knots of new star formation. Credit: NASA/ESA
Even their shapes could have changed. It takes time for the graceful arms of a spiral galaxy like our own Milky Way to evolve. Many young galaxies have a tattered appearance due to random mergers with other small, nearby galaxies in their youth.
In the Groth strip, foreground galaxies are larger and younger; those most remote appear like stellar dots.
“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 Marc Davis, professor of astronomy at the University of California at Berkeley.
Hubble sees the galaxies from pre-teen chaos evolving into the more common types of spiral and elliptical galaxies seen in the current era. Funny how the galactic life cycle shares something in common with the human.
Other discoveries made from the photo include the general galactic texture – clumps of galaxies separated by more scattered regions – indicating dark matter at play, a giant red galaxy with dual black holes in its core and a whole lotta oddball galaxies to keep astronomers busy writing papers for a long time.
Ultraviolet view of the Extended Groth Strip taken with the Galaxy Evolution Explorer (Galex) and available on Google Sky. Credit: NASA
The Hubble picture was part of a much larger campaign called the All-wavelength Extended Groth Strip International Survey (AEGIS) involving four orbiting and four ground-based telescopes utilizing everything from visible light to radio waves to X-rays to map this strip of sky in every color of light possible. If you’re game to explore some of these, I invite you to explore the Interactive Groth Strip on the AEGIS site. The various sky views are also found at Google Sky as options at the bottom of the atlas page.