infrared deep field

Once again, the Earth-orbiting Hubble Space Telescope (HST) has gone where no telescope has gone before, looking farther into space and further back in time. Indeed, astronomers guess that the galaxies the orbiting observatory recently glimpsed in this infrared image may have formed some 12 billion years ago, when the universe was still in its infancy.

comparison

COMPARISON. The distant galaxy in the visible-light picture (top) looks uncharacteristically lumpy because the WFPC2 can detect only the bright blue knots of star birth. Infrared images of the same galaxy taken with NICMOS (bottom), however, reveal the underlying disk structure, containing older stars.

"These are the deepest images of distant galaxies that have ever been obtained," said Rodger I. Thompson of the University of Arizona, in early October. Thompson led this latest HST study, the results of which are due to appear in the Astronomical Journal.

The pictures help resolve a mystery that surfaced three years ago, when HST last focused on this patch of sky, dubbed the Hubble Deep Field. The telescope's optical Wide Field/Planetary Camera 2 (WFPC2) trained its lens on the deep field for 10-hour exposures in 1995, photographing many new galaxies. In doing so, it also caught on film a few peculiar objects that resembled lumpy knots of blue light.

Thompson's team finally got a good look at these odd clumps thanks to an infrared camera--the Near Infrared Camera and Multi-Object Spectrometer (NICMOS)--mounted on HST last year. Because the universe is continuously expanding, light emanating from the farthest galaxies--those at the very fringes of the universe--is "redshifted." In other words, its wavelength is stretched beyond the visible range and into the infrared.

In January 1998, NICMOS opened its shutter onto a section of the deep field for 36 hours. Its greater resolving power showed that the lumpy objects in the optical deep field exposures were in fact areas of intense star formation within ordinary--albeit ancient--star systems. The underlying structures of these distant galaxies, made clear by NICMOS, were simply not hot enough for the WFPC2 to record. NICMOS also revealed a slew of previously unknown celestial outlayers.

Studying these galaxies in detail will help astronomers better characterize the birth of the universe and judge its age. To determine the exact nature and distance of these galaxies, though, they will need an instrument more powerful than NICMOS. The good news is that just such a device--one that can measure all the necessary infrared spectrums--is planned for HST's progeny, the Next Generation Space Telescope, scheduled for launch in 2007.

Eight years isn't such a long wait to see back to the beginning of time.