A New Science Strategy for Space Astronomy and Astrophysics (1997) / Chapter Skim
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4 Galaxies and Stellar Systems
4 Galaxies and Stellar Systems
Pages 35-46
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From page 35... ...
The internal structure of a star depends on its chemical composition, and so do its other properties, including how long it will live. Moreover, the chemical composition of the material in dense clouds- the sites of new star formation determines the cloud's transparency, and the energy that is trapped influences the conditions under which new stars are born.
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From page 36... ...
Key Questions About the Development of Present-Day Structures Key questions to be addressed in studies of the development of present-day structures include the following: · How do the distribution of galaxy properties such as size and mass, and the variety of their morphological forms, relate to the physical conditions of the universe in its first billion years? · What triggered the birth of the first generation of stars?
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From page 37... ...
In addition, observations of CO at millimeter wavelengths reveal that large masses of molecular gas have been found around some of the highest-redshift quasars, implying enormously energetic star-formation episodes at this early time. Recent numerical simulations of the evolution of dissipationless particles (including dark matter)
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From page 38... ...
Key Questions About Chemical Composition Thanks to the increasing amount of high-quality spectroscopic data on elemental abundances in stars and in the gas of high-redshift systems, unprecedented progress in the study of the chemical evolution of the universe is possible in the near future. Answers to a number of key questions will guide future understanding of the history of star formation and nucleosynthesis in galaxies.
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From page 39... ...
Future Directions for Understanding Chemical Composition The future directions identified below are intended to elucidate the history of star formation, the major factor in compositional evolution. Critical issues to be examined with the next generation of instrumentation include the following, in no particular order: Measuring the composition of the gas, dust, and stars of which the universe is composed, as a function of redshift.
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From page 40... ...
Future Directions for Understanding Dark Matter Future directions for the study of dark matter include the following, in no particular priority: 1. Detecting dark matter through its gravitational influences on the light from distant objects.
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From page 41... ...
· How can observers identify the gaseous predecessors of galaxies? Recent Progress in Understanding Baryons Outside of Galaxies r G ~ For years, astronomers have had two sets of observations demonstrating that gas exists between the galaxies: as just mentioned, numerous absorption lines seen in the spectra of high-redshift quasars, and x-ray observations of the hot intracluster gas in nearby clusters of galaxies.
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From page 42... ...
If, as most theoretical studies indicate, rich clusters are fair samples of the universe, this result suggests that the density of the universe is only one-third of the critical density. Many poor groups of galaxies have large dark-matter halos as well, and so it may well turn out that a significant fraction of the baryonic dark matter in the universe resides there.
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From page 43... ...
Key Questions About Supermassive Black Holes and Quasar Power Sources The details of the physical processes governing the formation and growth of supermassive black holes, the prodigious luminosities of quasars, and the evolution of quasars (both collectively and individually) are still far from being resolved.
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From page 44... ...
. Recent Progress in Understanding Supermassive Black Holes and Quasar Power Sources If quasars are considered as marking the locations of supermassive black holes, an empirical statistical picture of the origin and growth of supermassive black holes can be made by conducting a census of quasars up to high redshifts and down to low luminosities.
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From page 45... ...
To answer the key questions relating to supermassive black holes requires the following necessary efforts: .
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From page 46... ...
In particular, the dynamical, structural, and chemical evolution of the various structures are all fundamental and need to be pursued. Opportunities include mapping the temperature distribution, kinematics, and chemical composition of x-ray-emitting gas in clusters, and detecting weak absorption lines at high spectral resolution at ultraviolet wavelengths.
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