Hubble Deep Field Image
Research Using Data from the Hubble Space
Telescope Examines the Most Distant Galaxies
The first stars apparently started brightening
the dark, infant universe just a few hundred million years after
the big bang in an explosion of light unrivaled since the dawn
of space and time.
After a detailed analysis of the most sensitive images ever
taken by the Hubble Space Telescope, a team of researchers
concluded that the early universe was a much brighter place
than had been assumed. "Previous measurements have missed a
dominant fraction of the light from the most distant
galaxies," Kenneth Lanzetta of the State University of New
York at Stony Brook said at a NASA news conference. "Our
results indicate the distant universe contained far more
light, and hence far more stars, than was previously
believed," he added. "In fact, we find as we look toward
greater and greater distances, that is toward earlier and
earlier times, the star formation activity of the universe
increases to the earliest times we can see."
Lanzetta's team analyzed three so-called Hubble Deep Field
images, the equivalent of ultra-long time exposure
photographs of visually empty patches of the northern and
southern skies. All but about 150 of the galaxies were too faint for
the follow-on spectroscopic measurements needed to pin down
precisely how far away -- and thus how old -- each star
swarm might be. Even so, astronomers were able to use other
techniques to determine that the dimmer, more reddish
galaxies dated back to roughly a billion years or so after
the big bang. Lanzetta's team developed a subtle new
technique for analyzing the deep-field galaxies, carefully
characterizing the color variations that provided clues to
their actual distances.
The correction factor, in effect, added back the light "missing" from more distant galaxies. Finally, the
researchers included a measure of the gas density of the
early universe based on the spectroscopic analysis of
remote quasars. In the nearby, "local," universe, high gas
density implies high rates of star birth. Putting it all
together, the researchers were able to turn the
two-dimensional Hubble Deep Field images into a
three-dimensional look back toward the big bang. "What we
have realized is that even the deepest, most sensitive
images of the universe ever obtained by the Hubble Space
Telescope . . . are not sensitive enough to detect most of
the light of the very most distant galaxies recorded,"
Lanzetta said. "That light is just too faint, and it's been
missed by all previous measurements." In other words, he
said, the raw Hubble images reveal the tip of the iceberg
"and the bulk of the iceberg is missing." "What we've done
is develop a technique to account for this missing light,
and we have found that the distant early universe contains
far more light, and hence far more stars, than was
previously believed," Lanzetta said.