Because light travels at a finite speed, the farther away a detected object is, the longer it has taken the light to get here.
The ultra deep survey surpasses two earlier surveys, known as the Hubble Deep Fields, which revealed thousands of new galaxies dating back as far as when the universe was only a billion years old. Last week, astronomers using the Very Large Telescope at the European Southern Observatory said they had discovered a galaxy from when the galaxy was just 470 million years old. Its incredibly faint light had been amplified by the curvature of space around a giant cluster of galaxies. If confirmed, that would be the record.
But the ultra deep field has the sensitivity to reach back to galaxies when the universe was only 300 million years old, without the aid of any gravitational amplification. The Hubble thus opens to exploration the period of time from 300 million to 700 million years of age, when, theorists suggest, the first galaxies were burning themselves out of the murk that descended when the fires of the initial Big Bang cooled. Dr. Massimo Stiavelli, of the telescope institute, called those years a crucial period in the early life, "a teething for the universe." He added, "Hubble takes us to within a stone's throw of the Big Bang itself."
The new survey actually has two parts: the million-second exposure with Hubble's jazzy new Advanced Camera for Surveys, installed in 2002, led by Stiavelli, and a shorter exposure of the same patch of sky with another camera sensitive to infrared light, the Near Infrared Camera and Multiobject Spectrometer, Nicmos, led by Dr. Roger Thompson of the University of Arizona.
Another team, led by Dr. Sangeeta Malhotra of the telescope institute, is still reducing data from a spectrograph on the Advanced Camera for Surveys, which will help astronomers eventually identify the distances and types of objects in the picture.
Like the earlier deep fields, the ultra deep field shows that the early universe was littered with galaxies of oddball shapes and colors, but astronomers homed in on a few dozen soft reddish dots, which appear on the Nicmos image but not on the visible-light image.
While these might turn out to be dim nearby stars known as brown dwarfs, some astronomers were excited about the possibility that they might be the most distant objects ever seen, galaxies just emerging from the dark ages. Because the universe is expanding, galaxies at great distances are being carried away at high speeds and their visible light is lengthened and stretched -- "redshifted" in the jargon -- to longer wavelengths. The farther away they are, the more of their light becomes infrared radiation. Galaxies when the universe was only 300 million years old would be moving so fast that all their light would be invisible infrared radiation.
If the red dots are distant galaxies, then the Hubble might finally have hit the wall. Hubble's successor, the Webb telescope, is being built to observe infrared radiation in order to pursue such galaxies. "The dark ages are James Webb territory," Thompson said.
RSS