Most distant galaxy cluster found

By PHIL BERARDELLI, UPI Deputy Science and Technology Editor  |  April 10, 2002 at 11:05 PM
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WASHINGTON, April 10 (UPI) -- An international team of astronomers said Tuesday it has discovered the most distant and oldest group of galaxies ever seen.

Using the European Southern Observatory's Very Large Telescope or VLT Array, the astronomers viewed a cluster of galaxies estimated to be 13.5 billion light-years away. The cluster is so distant it has taken nearly the entire age of the universe for its light to reach Earth.

The discovery of the galactic cluster is important, the astronomers said, because it offers a glimpse of the universe at a relatively young age. The VLT image portrays the cluster when the universe was only about 1.5 billion years old or 10 percent of its current estimated age of 15 billion years.

"It is another important step in the process of understanding the transition from a smooth universe to a lumpy universe," team leader George Miley, of Leiden University Observatory in The Netherlands, told United Press International.

Miley explained that astronomers still do not understand completely how the nearly uniform energy that was released in all directions by the Big Bang -- the enormous expansion of space and time that gave rise to the universe about 15 billion years ago -- evolved into the seemingly random and irregular structures that comprise the visible universe.

In general, astronomers believe that the universe evolved along a hierarchy of structures of ever-increasing size, from stars, to galaxies, to clusters of galaxies, to superclusters -- the largest structures known, which can contain hundreds of galaxies and stretch for hundreds of millions of light-years.

So far, most of what astronomers understand about this process has been theoretical. The evidence has been pieced together from some observational data combined with mathematical models, Einstein's Theory of Relativity and other indirect sources.

Little by little, however, the world's most powerful telescopes, such as the VLT's quartet of 8.2-meter mirrors, located at Atacama, Chile, are beginning to provide astronomers with direct evidence. The latest galactic cluster image has furnished another piece of the puzzle, Miley said. "It gives us a glimpse of the universe at its baby time. We know that galaxies began to form around this time, but we didn't know when they began to form in groups."

Astronomers search for the most distant celestial objects by first aiming powerful radio telescopes -- which can detect radio signals from outer space -- toward peculiar galaxies called radio galaxies. These objects emit extremely powerful radio signals that are believed to be caused by super-massive black holes at their centers. The signals are generated by the violent processes that occur when black holes suck in all the nearby galactic matter.

The black holes within radio galaxies are believed to be thousands of times more massive than the black hole now known to exist at the center of the Milky Way.

Most -- but not all -- radio galaxies tend to have existed in the early universe. They appear to be at the heart of the youngest galactic clusters. Miley said radio galaxies act as "signposts of early cosmic meeting points." As predicted, the VLT discovered the distant galactic cluster in the vicinity of an ancient radio galaxy.

"Just simply knowing that these objects merely exist puts pressure on existing models of the universe," team member Will van Breugel, an astrophysicist with Lawrence Livermore National Laboratory in Berkeley, Calif., told UPI.

Current theory requires at least one billion years for galaxies to form, van Breugel explained. Clusters of galaxies, in theory, should take much longer. But this cluster of galaxies appears to have formed only 1.5 billion years after the Big Bang, which calls such theory into question.

"The modelers of early galaxy formation may have some work to do," said Hy Spinrad, professor of astronomy at the University of California at Berkeley.

On the other hand, Spinrad told UPI, most early-universe, non-radio galaxies tend to be less structured than modern galaxies, so they may still work within existing models. "These (early) galaxies are pretty wimpy compared to our Milky Way," he said.

Nevertheless, Spinrad praised the ESO team's work as especially impressive because it has confirmed the cluster's distance by obtaining the "red shift" of 20 of its constituent galaxies. Red shift is the stretching out of light wavelengths that occurs when objects travel at great speeds. The most distant galaxies are the fastest travelers in the Universe, according to a universally accepted system of measurement that was developed by American astronomer Edwin Hubble in 1929.

Richard McMahon, lecturer at the Institute of Astronomy at the University of Cambridge, England, believes the discovery of the cluster is important because it demonstrates a powerful new technique that can be used to find even more distant and ancient celestial objects.

"What we'd really like to know now is how many more of these (clusters) there are," McMahon told UPI.

Meanwhile, the ESO team plans to map out more of the cluster already discovered. "We have not seen the (entire) structure," van Breugel said. "Maybe (the image is) just the central piece." He explained that despite the distance involved, the VLT was able only to capture a portion of the cluster.

"The bigger the telescope, the smaller the field of view," van Breugel said. "So we need to study (the cluster) with better resolution."

Miley said the team next will observe the cluster using the Advanced Camera for Surveys, a powerful new instrument recently installed on the orbiting Hubble Space Telescope. The ACS will help the team determine the full size of the ancient object.

"We have now scheduled this particular target for one of the deepest observations ever to be made with the (Hubble)," he said.

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