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Astronomy and Astrophysics in the New Millennium
FIGURE 2.11 Simulation of two neutron stars spiraling into each other, ejecting hot gas (orange filamentary structures) and neutron-rich matter (blue/green, snail-shaped structure) in the process. Green represents higher-density matter than does blue. Gamma-ray bursts could be produced by such mergers. The white dots represent background stars added for visual effect. Simulation by P. Gressman (Washington University in St. Louis), and visualization by W. Benger (Max-Planck-Institut fur Gravitations Physik, Konrad-Zuse-Institut). Courtesy of the NASA Neutron Star Grand Chal-lenge Project.
be able to observe this emission from the first clusters of galaxies that form in the universe, revealing how they formed. Complementary observations with NGST and GSMT will show the evolution of clustering in cosmic time and how the cluster environment affects the evolution of galaxies.
As remarked above, present observations of galaxies do not extend much beyond a redshift of 5. The time between the “recombination” epoch at a redshift of about 1,000, when the cosmic background radiation was emitted, and that of redshift 5 remains completely unexplored. This period contains the “dark ages,” when the visible light of the Big Bang faded and darkness descended. The dark ages ended with the formation of the first stars and galaxies—the dawn of the modern universe. The new decade brings the possibility of seeing the first generation of stars and galaxies that mark this dawn. NGST is designed to have the sensitivity and wavelength coverage to detect light from the first generation of galaxies, out to a redshift of about 20. With NGST it will be possible to address a number of fundamental questions: When did the first galaxies and stars form? What is the history of galaxy formation in the universe? What is the history of star formation and element production in galaxies? The ability of ground-based optical and infrared telescopes to address these questions is severely compromised by the opacity and the thermal emission from the atmosphere at wavelengths longer than 2 µm. NGST will cover the spectrum out to wavelengths of at least