ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, January 21, 1996 TAG: 9601200005
SECTION: HORIZON PAGE: F-1 EDITION: METRO
DATELINE: SAN ANTONIO, TEXAS
SOURCE: JOHN NOBLE WILFORD THE NEW YORK TIMES
As if peeking through a keyhole on the inner sanctum of the universe, the Hubble Space Telescope focused for 10 consecutive days last month on one especially narrow sector of the sky, taking long-exposure photographs deeper into space than ever before and recording the bewildering number and variety of galaxies stretching back toward the beginning of time.
One thing was stunningly clear: with this one achievement, the estimated galactic population of the universe had multiplied enormously - to 50 billion, five times as many as previously estimated. The Sun is one of 50 billion to 100 billion stars in the Milky Way, generally considered to be an ordinary galaxy.
Astronomers, clearly excited, made public a glittering mosaic of the pictures last week at a meeting of the American Astronomical Society. They described it as the deepest, most detailed view of the universe ever attained by optical astronomy.
Dr. Robert E. Williams, director of the Space Telescope Science Institute in Baltimore, said that this narrow segment of space ``will become the most intensively studied region in the sky in the coming decade.'' .
The observed slice of the heavens was no wider than 1/25 of one degree, equivalent to the size of a grain of sand held at arm's length. Yet in that space, astronomers reported counting 1,500 to 2,000 galaxies. Some are so small or far away that they are four billion times fainter that the dimmest object that the naked eye can see from the ground, 10 times fainter than the deepest existing ground-based observations have detected.
Astronomers are not sure whether they have finally glimpsed the earliest epoch of galaxy formation, which is thought to have begun when the universe was much smaller and no more than 5 percent to 10 percent of its present age. But they expected that more detailed analysis of these pictures and further Hubble photography of the same region, combined with observations by some of the world's most powerful ground-based telescopes, should lead to a better understanding of how galaxies form and evolve and when these processes began in the young universe.
Astronomers were especially impressed by the variety of the galaxies revealed in the composite picture. There were the familiar spiral and elliptical galaxies and some irregular shapes previously recognized. Others were linear or bore no resemblance to anything seen before. Perhaps some of these were the shapes of galaxies in early stages of formation.
At a news conference, Williams, the director of the telescope institute, said: ``You can see a myriad of galaxies. There are large ones and small ones, red ones and blue ones, very structured ones and also very amorphous ones. Most of these galaxies were never seen before Hubble. But we don't know the significance of all this yet.''
Nor is it known how the discovery would change astronomers' estimates of the number of stars there are in the visible universe.
``We now find there are as many galaxies in the sky as there are stars in our own galaxy,'' Dr. Andrew Fruchter, an astronomer at the space telescope institute, said in an interview.
Of course, no one knows exactly how many stars are in the Milky Way. Another astronomer said the estimate could be closer to 100 billion stars, not 50 billion. Other galaxies are probably larger, and many are smaller, clumps of stars numbering in the billions each.
In any case, this more expansive cosmic view is a far cry from that in the beginning of this century, when astronomers assumed the Milky Way was all there was, the universe entire. In the 1920s, the orbiting telescope's own namesake, Edwin P. Hubble, was the first to establish beyond doubt that a multitude of separate galaxies comprised the universe, their number now exceeding his dreams.
For the new survey, directed by Williams, astronomers chose what they called an undistinguished sector of the sky near the handle of the Big Dipper, part of the constellation Ursa Major. This was a region relatively uncluttered by foreground stars or nearby galaxies. Yet it was considered representative of the typical distribution of galaxies because the universe, statistically, looks largely the same in all directions.
The Hubble telescope's wide-field camera took pictures one after another Dec. 18-29. Each exposure was typically 15 to 40 minutes. Separate images were taken through filters for ultraviolet, blue, red and infrared light. These were combined into a single color composite picture, each addition revealing greater depths of view and fainter objects.
Only the Cosmic Background Explorer satellite six years ago managed to look deeper in space, the project astronomers said, but it was observing radiations left over from the Big Bang, the explosive event theorized to be the origin of the universe, and did not produce images of detailed structure out at the cosmic fringes.
In the few days astronomers have had to analyze the Hubble pictures, they struggled to understand details of what they were seeing.
Dr. Mark Dickinson, another member of the research team from the space telescope institute, said their galaxy count was somewhat imprecise because they could not be sure whether some fuzzy points of light represented a single galaxy of irregular shapes or a clump of two or more neighboring galaxies.
The extremely faint objects were a problem, too. Because astronomers had no reliable measure of their distances, they could not tell whether the objects were faint because they were dwarf galaxies at no great distance, young galaxies just forming or galaxies far out at the edge of the visible horizon.
Others with especially indistinct shapes might be proto-galaxies. Perhaps, astronomers said, the Milky Way looked like this 10 billion years ago, before evolving into its present spiral shape. In astronomy, the more distant an object, the earlier it is in time. So until they can determine the distances of these objects, astronomers will be unable to draw conclusions on whether galaxies for the most part formed early in a burst of creation or have come into being steadily until fairly recent times.
The researchers likened their achievement to an archeological dig. In particular, they compared it to archeologists finding ruins of a royal city, sensing they have something big but not knowing its age.
``There is no evidence that we are seeing back to the point of first galaxy formation,'' Williams said. But the great number of faint galaxies led the astronomers to suspect they were close.
Astronomers at ground-based telescopes are examine the light properties of prominent objects in the survey region to determine their distances. Other ground-based and space-based telescopes are expected to study the region in other wavelengths, from X-ray through radio. More sensitive instruments planned for installation on the Hubble telescope next year and in 2001 should also answer some of the many questions about the findings.
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