HUBBLE DISCOVERS BILLIONS OF GALAXIES.

Byline: 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 achieved 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 here Monday 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.

Robert E. Williams, director of the Space Telescope Science Institute in Baltimore, said 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 a 25th 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 than 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," 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 standing near Fruchter interrupted to say the estimate could be closer to 100 billion stars, not 50 billion. Other galaxies probably are 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 that 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 from Dec. 18 to Dec. 29. Each exposure was typically 15 to 40 minutes long. 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.

CAPTION(S):

PHOTO

Photo (color) These images represent select portions of the deepest, most detailed view of the universe ever attained by optical astronomy. Associated Press