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Optical
image of one of the pillars of the Eagle Nebula. New stars are
embedded inside the finger-like structures extending from the
tip of the pillar.
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Like
the giant galaxies in which they appear, stars and their planets
form when clumps of gas and dust contract to much smaller sizes.
During the first phases of star formation, each of these contracting
clumps was too cool to produce visible light. Within these clumps,
the attraction of each part for all the other parts caused the clumps
to shrink steadily, squeezing their material into ever-smaller volumes.
As the clumps continued to contract, the resulting increase in density
caused a corresponding rise in temperature at the clumps' center.
Eventually, as this central temperature rose above 10 million degrees,
atomic nuclei began to fuse. The onset of nuclear fusion, which
marks the birth of a new star, occurred nearly 5 billion years ago
in the case of our Sun. In the case of the oldest stars that shine,
this onset of nuclear fusion began 10 to 14 billion years ago.
During
the later stages of the contraction process, a rotating disk of
gas and dust formed around the central mass that would become a
star. To detect these protoplanetary disks, the precursors of planetary
systems around stars that are in the process of formation, requires
telescopes with an improved angular resolution, sufficient to reveal
more than the disks’ bare outlines. We now know that other stars
have planets, as revealed by recent astronomical measurements that
detected the pull exerted on their stars by large, Jupiter-like
planets.
Many
of the initiatives recommended by the Astronomy and Astrophysics
Survey Committee will address the origins of stars and planets.
NGST and GSMT will probe the dusty environments of star-forming
regions with unprecedented sensitivity and angular resolution. Existing
ground-based telescopes will be made much more powerful through
new instruments provided by the Telescope System Instrumentation
Program. Protoplanetary disks are much cooler than stars and emit
most of their radiation in the infrared region of the spectrum.
To permit observations in the far infrared, the committee recommends
the development of the Single Aperture Far Infrared Observatory
(SAFIR). Observations at millimeter and different infrared wavelengths
will enable astronomers to measure the concentrations of different
species of atoms and molecules in the disk. It will also be possible
to determine the speeds at which these particles are moving and
the temperatures to which they have been heated.
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