Stretching the vision of NASA's Hubble Space Telescope farther across space and further back into time than ever before, astronomers have peered into a previously unseen realm of the universe.
A "long exposure" infrared image taken with Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) has uncovered the faintest galaxies ever seen.
Astronomers believe some of these galaxies could be over 12 billion light-years away (depending on cosmological models) – making them the farthest objects ever seen. A powerful new generation of telescopes will be needed to confirm the suspected distances.
"NICMOS has parted the dark curtain that previously blocked our view of very distant objects and revealed a whole new cast of characters. We now have to study them to find out who, what and where they are. We are still finding new frontiers," says Rodger I. Thompson of the University of Arizona in Tucson.
"This is just our first tentative glimpse into the very remote universe," says Alan Dressler of the Carnegie Observatories in Pasadena, CA. "What we see may be the first stages of galaxy formation. But the objects are so faint that their true nature can only be explored with the advanced telescopes of the future."
"This observation is a major step toward fulfilling one of Hubble's key objectives: to search for the faintest and farthest objects in the universe," adds Ed Weiler, NASA's acting Associate Administrator for Space Science.
In a separate discovery, Thompson also found that faint red galaxies matched up with compact blue knots of light seen in the earlier visible light image. "This means that some objects that appeared to be separate galaxies in the optical image are really hot star-forming regions in much larger older galaxies," he says.
Prior to the NICMOS observation, a ten-day long exposure called the Hubble Deep Field was Space Telescope's benchmark for the "deepest" view into the universe (with the exception of the cosmic microwave background that is farther away than any structures seen in the universe).
Astronomers had to wait for the infrared camera to be installed on Hubble to look for unseen galaxies beyond the limits of the visible deep field photograph. Infrared sensitivity was needed because the expansion of the universe is expected to stretch the light of distant galaxies down to infrared wavelengths.
Thompson selected a portion of the original Hubble deep field and took long exposures with the Hubble's near infrared camera. When the infrared and visible-light pictures were compared, Thompson found many new objects that were not seen in visible light.
In results to be published in the Astronomical Journal, Thompson precisely measured the infrared "colors" of the objects. He found some objects that had the expected color of a galaxy too distant to be detected in the optical HDF.
Scheduled for launch in the year 2007, the Next Generation Space Telescope (NGST) will be used to take infrared spectra of candidate galaxies to confirm their distances, and its higher resolution will help reveal the shapes of these early objects.
NASA Headquarters, Washington, DC
Goddard Space Flight Center, Greenbelt, MD
Space Telescope Science Institute, Baltimore, MD