- BALTIMORE -- These galaxies
are long ago and far away, thousands of them, the earliest and most distant
ever photographed.
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- 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 they are all waiting in what looks like
an "empty" spot of sky just one-tenth of the diameter of the
moon.
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- "The field itself is just beautiful, just rich with
different things," said Steven V.W. Beckwith, director of the institute.
He gathered a half-dozen Ultra Deep Field astronomers around his computer
screen last week for their first glimpse of the project's results -- some
of the earliest galaxies to form after the Big Bang.
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- 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. "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."
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- 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. Looking back 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.
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- 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.
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- 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. Analysis
of the light from each object will reveal how long ago the light left it,
and how distant it is.
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- To see to 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 both 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.
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- 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.
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- 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 will continue until the end of the year. The final image will
be made available to astronomers worldwide in February.
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- When the project's scientists gathered in Beckwith's
office 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." By year's end, the
Ultra Deep Field will turn up objects four times fainter.
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- As the astronomers searched the screen, they saw 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
they took to be young spiral galaxies, seen edge-on before they have been
swollen by mergers with other galaxies.
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- 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.
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- 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. "We're within spitting
distance," he said.
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