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Image
of tine fluctuation in the universe's oldest light, only 300,00
years after the Big Bang. There is no way for astronomers to
see farther back than this electromagnetic brick wall. Future
tools for detecting gravitational radiation offer the promise
of breaking through this wall to even earlier times.
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Astronomy
is history. Because light takes time to travel from one place to
another, we see objects not as they are now but as they were at
the time when they released the light that has traveled across the
universe to us. Astronomers can therefore look farther back through
time by studying progressively more-distant objects.
The
chief difficulty in employing this "time machine" to observe
the cosmos during its past epochs arises from the fact that distant
objects appear fainter than closer ones. We must therefore capture
and analyze the light from progressively dimmer objects as we push
farther back into the past. Specialized instruments are needed to
study our nearest neighbor, the Andromeda Galaxy, which is 2 million
light-years away. But this companion of the Milky Way shines a million
times more brightly than a similar galaxy seen at a distance of
2 billion light-years! This comparison gives a sense of how difficult
it will be to obtain images of objects formed close to the Big Bang
era more than 10 billion years ago.
During
the past few years, the Hubble Space Telescope has obtained long-exposure
images that reveal the faintest objects ever detected. Some of these
objects are galaxies seen during their early developmental stages
when they were rich in young, hot, and very luminous stars. To peer
still farther back through time, to reach the era when stars first
began to shine, astronomers need a telescope that can detect extremely
low intensities of infrared light. Astronomers need sensitivity
in the infrared part of the spectrum because the light from these
young stars in distant galaxies, even though emitted as visible
light, has been stretched by the expansion of the universe to appear
to us as infrared light.
The
Hubble Space Telescope can observe the shortest-wavelength portion
of the infrared domain, but its 2.4-meter mirror is too warm and
too small to detect the faint glow from the most distant young galaxies.
To observe galaxies in their earliest epochs, the survey report
recommends a new, advanced- technology telescope designed to work
best in the infrared part of the spectrum. In an orbit a million
miles from Earth, this telescope will become so cold that its own
infrared glow will be insignificant compared with the light from
the distant galaxies, something an earthbound telescope could never
achieve. Also, being above Earth's veil of air allows us to see
radiation that cannot penetrate it, and guarantees the sharpest
images the telescope can deliver, free from the turbulence in Earth's
atmosphere that handicaps telescopes on the ground.
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