Survey looks back at early universe
Combined study traces galaxies, their evolution
Published 5:30 am, Tuesday, June 24, 2003
Welcome to the early universe, less than a billion years after the big bang: It's a violent place where the rate of star birth has surged with amazing speed to baby boom proportions, but the young stars are clustered in galaxies so small and weak that they may be unable to save their inner monsters -- black holes -- from starvation.
Five billion years later, the galaxies have grown into hulks by accreting or colliding with one another, and they now harbor an impressive population of super-massive, gluttonous black holes.
But the galactic growth rate is trailing off. In another billion years, the star birthrate will drop even more abruptly to about one-tenth the rate of the earlier boom.
The era of major cosmic construction has subsided, and the universe is only about half its present age of 13.7 billion years. (The sun and Earth will not be born for another few billion years.)
These rare snapshots of the growing universe are some of the initial findings, released Thursday, from the broadest in-depth survey ever conducted of the evolution of the largest cosmic building blocks -- galaxies.
Among the survey's intriguing discoveries are seven mystery objects that could be the most distant black holes ever detected.
"This is the first time that the cosmic tale of how galaxies build themselves has been traced reliably to such early time," said Mauro Giavalisco, leader of the Hubble Space Telescope's part of the survey.
He compared it to seeing a human at the age of 5 or 6. "We really are inching back to see the toddler and the infant at delivery -- though we can't see that quite yet."
The international effort, known as GOODS, for Great Observatories Origins Deep Survey, combines NASA's major observing platforms in space with the world's largest ground telescopes.
The effort, Giavalisco said, so far has taken several years, more than 100 scientists and "pretty much the largest mirrors on the planet." It has generated at least 15 papers, which are undergoing peer review for a special issue of the Astrophysical Journal Letters.
The survey's two images -- of the Northern and Southern skies -- show a total of about 50,000 galaxies across a wide range of distances, ages and growth stages.
The findings to date come primarily from the Hubble telescope and the Chandra X-ray Observatory. NASA's Space Infrared Telescope Facility (SIRTF) is to join the effort after its launch, scheduled for August.
This combination of instruments enables astronomers to examine the same patch of sky at different wavelengths and to reveal a variety of properties in sharper detail and with higher sensitivity over greater distances than ever before, the astronomers said.