Astronomers seek to understand phenomena as diverse as the formation of planets, the origin of solar activity, the evolution of black holes, and the large-scale structure of the universe. Electromagnetic radiation—radio, infrared, optical, ultraviolet, x-ray, and gamma-ray—provides most of the information we have on these distant phenomena, but other messengers can contribute as well: Energetic charged particles (the cosmic rays) carry information about where they were accelerated, neutrinos tell us about the deep interior of stars, and gravitational waves may reveal how some black holes form. This chapter describes how the recommended new initiatives grew out of the existing program, how they complement each other, and how they will address the major scientific questions in astronomy. The characteristics of the major and moderate new initiatives are listed in Tables 3.1 and 3.2. More detailed descriptions of the facilities and the science they will accomplish can be found in Astronomy and Astrophysics in the New Millennium: Panel Reports (NRC, 2001).

The committee emphasizes that telescopes alone do not lead to a greater understanding of the universe. So that maximum benefit can be obtained from the current and proposed new facilities, the committee recommends a vigorous and balanced program of astrophysical theory, data archiving and mining, and laboratory astrophysics. One of the key recommendations is the establishment of theory challenges to be associated with most new major and moderate programs. These challenges should describe theoretical problems that are ripe for progress, relevant to the planning and design of the program, and essential to the interpretation and understanding of its results in the broadest context. The specific theory challenges tied to each mission and project should be determined by the informed astronomical community—probably through ad hoc panels, drawn from the theory community and convened for this purpose. However, to illustrate the concept the committee gives examples of possible theory challenges below in the discussion of the new initiatives.


Ultraviolet, optical, and infrared (UVOIR) observations provide extremely important sources of information about the universe. Stars,

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