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Part
of the Hubble Deep Field image showing a myriad of spiral, elliptical,
and irregular galaxies in ther infancy billions of years ago.
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Galaxies
- enormous collections of hundreds of billions of stars - are the
basic assemblages of structure in the universe. A crucial question
in modern astronomy is, How did these objects begin to form?
The
Big Bang set the stage for the birth of stars and galaxies. Observations
with ground-and space-based radio telescopes have now shown that
the universe began almost entirely smooth, as a rapidly expanding
hot sea of particles and intense light that followed the Big Bang.
Within this sea rolled subtle waves. These gentle undulations in
matter and energy density grew slowly but steadily under the influence
of gravity. A few hundred thousand years after the Big Bang, the
strength of these ripples was only one- thousandth of a percent
above the smooth background. Although this process occurred long
ago, even today light continues to stream in from this ancient time,
and the primeval waves, destined to grow into great superclusters
of galaxies, are clearly seen by our most sophisticated instruments.
Over the hundreds of millions of years that followed, gravity continued
its work until giant clouds of cooling gas, the forerunners of today’s
galaxies, began to condense. Within these developed much smaller,
denser clouds that gave birth to stars. The light from this first
generation of stars, born some 12 to 13 billion years ago, brought
the dawn of the modern universe with the birth of countless points
of light that dot our night skies.
The
Hubble Space Telescope has carried us back to within a few billion
years of the Big Bang, allowing us to watch the growing up of young
galaxies. But the actual birth of galaxies remains beyond our grasp.
Within a billion years after the Big Bang, gravity had organized
galaxy-sized clouds of gas, and stars condensed within these clouds
and first ignited their nuclear furnaces. Looking back to that time
is the primary goal of the Next Generation Space Telescope (NGST),
the highest priority of the Astronomy and Astrophysics Survey Committee
for the new decade. NGST will allow astronomers to peer into the
distant past and see, for the first time, the birth of the modern
universe.
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