The Origins of Stars and Planets
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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