Team `within spitting distance' of the Dark Age of the universe

Project yields first images of the earliest galaxies

October 25, 2003|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

These galaxies are not only long ago and far away. They're also the earliest and most distant ever photographed. And there are thousands of them.

They're the galaxies of the Hubble Ultra Deep Field - the first fruits of a continuing project at the Space Telescope Science Institute in Baltimore.

Eventually, astronomers expect to capture the glow of tens of thousands of them. And the systems are all waiting in what looks like an "empty" spot of sky just one-tenth of the diameter of the moon.

"The field itself is just beautiful, just rich with different things," said Steven V.W. Beckwith, director of the institute.

Beckwith gathered a half-dozen Ultra Deep Field astronomers around his computer screen this week for their first glimpse of the project's results - some of the earliest galaxies to form after the Big Bang.

They glowed on the monitor in a bewildering variety of shapes and colors - neat pinwheels and messy blobs of silver and gold, thin, steely streaks and intense points of light as red as rubies. There were thousands of them, but it's only the beginning of an observation that is expected to continue into December.

"Think of the universe today as a 50-year-old person," Beckwith said. "The changes in people in their early formative years are much faster [than in later life]. This is also true of the universe."

The Ultra Deep Field observations will allow astronomers to peer backward to a time when the "50-year-old" universe was closer to 2 or 3. "We're really beginning to probe the universe in its infancy at this stage," Beckwith said.

It's those early transformational years that scientists most want to study.

Looking back in time is possible in astronomy because the more distant an object is, the longer it has taken for the light we see to reach Earth. So we see these objects as they appeared millions or billions of years ago.

Beckwith compared the Ultra Deep Field project to the deep sediment cores drilled by geologists studying the Earth's history. The deepest layers in the core will reveal things about the environment hundreds or thousands of years ago. As they move higher on the core, they can identify changes in that environment, and in the life forms that lived in it.

The Ultra Deep Field provides a similar "core," revealing objects along a continuum of time, from the relatively nearby and "recent" to the extremely distant and earliest objects. Careful analysis of the light from each object will reveal how long ago the light left it, and how distant it really is.

To see that far, Hubble scientists needed to target a region of the sky relatively free of the space dust that might block the faint light of distant galaxies. It also had to be empty of bright, nearby stars and galaxies that would wash out the view.

They also wanted a spot that could be seen from key ground-based observatories in the northern and southern hemispheres, and one with good "guide stars" to help Hubble find its target. "There weren't very many options - a handful," said astronomer and project coordinator Massimo Stiavelli.

Gathering light from so far away demands patience. The photons have traveled for billions of years, and they straggle, one by one, into the detectors in Hubble's Advanced Camera for Surveys. As more photons arrive, more objects become visible, and visible objects begin to reveal more shape and detail.

In all, Hubble will be focused on the same spot for 1 million seconds, during 400 orbits of the Earth. The observations began Sept. 24, and they will continue until the end of the year. The final image - a trillion bytes of data - will be made available to astronomers worldwide in February.

When the project's scientists gathered in Beckwith's office this week for their first look, only one-third of the photons they hope to gather had been received. But the new image had already surpassed earlier Hubble Deep Field images, to reveal the most distant stars and galaxies ever seen.

"It's like Lewis and Clark," Beckwith said. "This is when they got far enough west of St. Louis that no one from Europe had been there before. That's where we are today."

As the astronomers searched the screen, they chattered about the sheer number of small, irregular galaxies - "little train wrecks," Beckwith called them. They're clumps of stars, bits and pieces of galaxies in the earliest stages of assembling themselves into the large, graceful ellipticals and spirals visible in the nearby universe today.

There were razor-thin silver streaks, which the astronomers took to be young spiral galaxies, seen edge-on before they have been swollen by mergers with other galaxies. They also pointed out interacting galaxies caught ripping batches of stars from each other in a bit of gravitational arm-wrestling.

And there were plenty of compact red dots - believed to be the earliest and most distant galaxies in the field, their light stretched into redder wavelengths by the expansion of the universe.

"There's something for practically every astronomer to look at and do research on, just a treasure trove," said team member Michael Corbin.

At some point, Beckwith said, such extended probes of the deep universe will cease to find new objects. That will mean they have reached the "Dark Age," perhaps 300 million years after the Big Bang, before the first stars became visible.

The Ultra Deep Field will probe to within a few hundred million years of that dark era, Beckwith said. "We're within spitting distance."

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