Astronomy and Astrophysics in the New Millennium (2001) / Chapter Skim
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3. The New Initiatives: Building on the Current Program
3. The New Initiatives: Building on the Current Program
Pages 95-136
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From page 95... ...
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From page 96... ...
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.
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The number in front of the parenthesis therefore corresponds to the best spatial resolution. CSpectral resolving power is defined as X1/~.
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From page 98... ...
The number in front of the parenthesis therefore corresponds to the best spatial resolution. CSpectral resolving power is defined as 71/~.
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Recent advances in adaptive optics have substantially reduced this problem in the infrared, but it persists in the optical band, particularly for wide-field imaging. Together, ground- and space-based telescopes enable a comprehensive attack on many of the fundamental questions in astronomy.
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NGST will be far more capable than its space predecessors HST and SIRTF and its airborne predecessor SOFIA. Figure 3.2 compares the sensitivity of NGST with that of other space facilities at low spectral resolving power, which is appropriate in searches for distant galaxies and faint stellar objects.
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From page 101... ...
GSMTis a 30-m-class, ground-based, filled-aperture, segmented-mirror, optical and infrared telescope that will operate in the atmospheric windows over the wavelength range from 0.3 to 25 ,um. Adaptive optics will give it diffraction-limited performance down to wavelengths as short as 1 ,um.
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From page 102... ...
Figure 3.3 shows a comparison of the sensitivity of GSMT and NGST at various spectral resolving powers, demonstrating the power of NGST at low spectral resolution and longer wavelengths and the power of GSMT at high spectral resolution and shorter wavelengths. Furthermore, with the ability to add new instrumentation, a step that is not possible with NGST, GSMT can evolve its capabilities and become increasingly powerful.
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From page 103... ...
Nevertheless, the large size of GSMT means that substantial advances in telescope design and adaptive optics will be required if it is to be built for a reasonable cost. The committee recommends that this work commence soon so that construction of the telescope can begin in this decade.
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From page 104... ...
¢.:::,:': :':-:: :,:,: :,:: :,: :,: :':-:,:~:,::: :.:.:-: :': :.:: :,:':,:.:,:.:::: :-:::: :::-::::::::-::::-:::::-:-:::-::::-::-:-:-::-::::::-:::::::-:.:-: :X : ~.r; ~ ~:: .~: - : ~i.~:' ~, jy ~-~.~::'~,? : .- : :~ FIGURE 3.3 A comparison of GSMT to NGST for spectral resolving powers of R = 10 through 100,000 over a range of wavelengths.
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From page 105... ...
Keck Observatory Adaptive Optics Team. (This figure originally appeared in Publications ofthe astronomical Society ofthe Pacific ~/izinowich, P
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These missions address major problems across a broad range of astrophysics. Possible theory challenges for NGST are · To develop an integrated theory of the formation and evolution of large-scale structure in the universe, Lyman-cx clouds, galaxy clusters, and galaxies; and · To understand supernovae the mechanism of explosion, the spectra, and the light curves.
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From page 107... ...
LSST would also provide valuable data on steady sources: By adding the data from different nights, it would be possible to develop maps of galaxies down to very faint magnitudes. Such maps would make it possible to infer the structure of dark matter on large scales from the way in which the dark matter distorts the images of the galaxies through weak gravitational tensing.
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From page 108... ...
The philosophy of the TSIP is consistent with previous recommendations of A Strategy for Ground-Based Optical and Infrared Astronomy (the McCray report; NRC, 1995) , which also recognized the importance of such a program.
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SIRTF will make pioneering observations of the infrared emission from young, distant galaxies and will bring tremendous advances in the understanding of brown dwarfs, ultraluminous infrared galaxies, and the dusty disks that surround stars. SOFIA will provide higher-spectral- and higher-spatial-resolution studies of bright SIRTF sources and will make major contributions to research on nearby regions of star formation and the interstellar medium of nearby galaxies.
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From page 110... ...
Furthermore, the dust reprocesses much of the optical emission from the newly forming stars into this wavelength band. Similarly, the obscured central regions of galaxies, which harbor massive black holes and huge bursts of star formation, can be seen and analyzed in the far infrared.
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From page 111... ...
The greatest challenge facing TPF is the capability to enable study of the very faint radiation from an Earth-sized planet against the glare of the central star. Earth radiates roughly a million times less infrared radiation than does the Sun, and when viewed from the nearest star it is only about 1 second of arc in angle (roughly the angle made by a dime seen a mile away)
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From page 112... ...
TPF will reveal planets in the process of formation, clearing gaps in dusty protoplanetary disks; individual star formation regions in distant galaxies and in the central regions of galaxies where enormous bursts of star formation occur; and the accretion disks that feed enormous black holes in the centers of galaxies, producing quasars and related active galactic nuclei. · To ensure a broad science return from TPF, Me committee recommends that, in planning the mission, comparable weight be given to the two broad science goals: studying planetary systems and studying the structure of astronomical sources at infrared wavelengths.
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From page 113... ...
W observations are essential for tracing the evolution of the intergalactic gas that is too cool to emit x rays, and high-resolution W spectroscopy is essential to study the dynamics and composition of interstellar gas. Diffraction-limited, wide-field imaging enables a search for sources too faint to be discovered from the ground.
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AST will observe solar plasma processes and magnetic fields with unprecedented resolution in space and time, providing a unique opportunity to probe cosmic magnetic fields and test theories of their generation,
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2004 to 2010 X, EW, W O Magnetic fields STEREO 2004 to2008 O
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SDO will help determine the origin of sunspots and solar active regions, the causes of the emergence and evolution of magnetic fields on the solar surface, the origin of coronal mass ejections and solar flares, and the connections between the interior dynamics and the activity of the solar corona. An understanding of the magnetic processes leading to solar mass ejection and flares, as well as to the generation of slow and fast solar winds, is
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HIGH-ENERGY PHOTONS: CON-X, GRANT, VERITAS, AN D EXI S T Atoms and ions emit and absorb x rays with specific wavelengths or, equivalently, specific photon energies. Gas must be hot, with a temperature exceeding hundreds of thousands of degrees, to emit x rays, but gas and dust can absorb x rays over a wide temperature range.
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By observing magnetized gas falling into black holes, Constellation-X will probe the properties of spacetime near a spinning black hole, thereby testing strong-field general relativity. Neutron stars, by contrast, have a solid surface and emit x rays in a rich variety of spectral lines.
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Some gamma rays have energies characteristic of the nucleus of the atom from which they were emitted; others are produced by electrons that are more energetic than those that produce x rays. Relatively low energy gamma rays must be observed from space, but gamma rays with photon energies 119
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GLAST and VERITAS will both address important issues concerning jets from active galactic nuclei, the acceleration of cosmic rays, and the nature of gamma-ray bursts. A possible theory challenge for both GLAST and VERITAS is · To model the dynamics of and the emission from the relativistic jets that emanate from the vicinity of central black holes in active galaxies.
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Because energetic x rays are so penetrating, EXIST can discover supernovae embedded in molecular clouds and the luminous matter accreting onto supermassive black holes in the centers of galaxies that are obscured at lower photon energies by surrounding gas and dust. Finally, with its ability to perform high-energy-resolution, hard-x-ray spectroscopy of 121
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LISA will complement the ground-based Laser Interferometer Gravitational-wave Observatory (LIGO) , which is designed to study the much higher frequency gravitational waves from the coalescence of neutron stars and stellar mass black holes, as well as the core collapse of supernovae.
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Neutrinos are produced by nuclear reactions in the interior of stars like the Sun, in supernova explosions, and possibly in gamma-ray bursts and in the regions around supermassive black holes. Most existing neutrino detectors are designed to study the relatively low energy neutrinos from the Sun and are focused primarily on studying the physics of neutrinos; as such, they lie outside the purview of this report.
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Perturbations in this background caused by intervening hot gas in galactic clusters permit radio astronomers to locate these clusters and to view the large-scale structure of the universe. Relativistic particles, spiraling in magnetic fields, emit radio photons and have provided astronomers with the first views of the enormous jets emanating from the vicinities of black holes at the centers of galaxies as well as the high-energy particles accelerated by supernovae.
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The world's largest steerable antenna, the GET uses a unique design and active surface control. In addition to being the world's largest filled aperture, the Arecibo dish can undertake TABLE 3.6 Large Centimeter-Wave Radio Telescopes with Open Access 125 Angular Wavelength Resolutionb Project Nations Involved Aperturea Range (cm)
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The EVLA will produce images of protogalaxies with sufficient detail to determine whether AGN activity associated with a supermassive black hole precedes, is contemporaneous with, or follows bursts of star formation in galactic nuclei. A possible theory challenge for the EVLA is · To understand the roles of star formation and supermassive black holes in powering luminous active galactic nuclei.
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mission is a 25-m-class space antenna to be linked with the ground-based VLBA. It is recommended as a means of achieving the highest spatial resolution for bright sources such as jets emanating from near supermassive black holes in galactic nuclei.
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The high spatial resolution (as fine as 0.01 arcsec) and sensitivity of ALMA will allow unprecedented views of diverse astronomical phenomena ranging from comets and Kuiper Belt objects in the solar system, to planet-forming disks in nearby regions of star formation, to the structure of the interstellar medium in distant galaxies.
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THE COSMIC MICROWAVE BACKGROUND RADIATION The cosmic microwave background radiation was emitted early in the history of the universe, before stars and galaxies formed. The radiation was emitted with a spectrum dominated by optical and near-infrared radiation, but the expansion of the universe has increased its wavelengths by a factor of about 1,000, so that it is now concentrated in the millimeter and submillimeter parts of the spectrum.
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130 ASTRONOMY AND ASTROPHYSICS IN THE NEW MILLENNIUM TABLE 3.7 Ground-Based Millimeter- and Submillimeter-wave Telescopes Wavelength Project Nations Involved Band Aperturea Angular Resolutionb (arcsec) Existing and Approved Interferometers ALMA United States, Millimeter 64 x l2 m ° °°3 ( 0 3 mm )
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The search for extraterrestrial intelligence is far more speculative because researchers do not know what to search for. Radio astronomers have taken the lead in addressing this challenging
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The privately funded 1HT, which will be the first radio telescope built specifically for SETI research, is a good example of such an innovative approach, and it will pioneer new radio techniques that could be used in the SPA. TO E NATI O CAL Vl RACIAL O B 5 E RVATO RY AND OTHER HIGH-LEVERAGE, 5 MALL I N ITIATIVE5 The National Virtual Observatory (NVO)
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Theory challenges tied to major and moderate projects. These challenges should be administered as a competitive grants program that is budgeted and programmed as an integral part of its associated project.
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In addition to the above recommended initiative for laboratory astrophysics, the committee notes several proposed programs that will provide significant benefit to astrophysics. Direct laboratory simulation of magnetic reconnection in plasmas and of radiative-hydrodynamical instabilities in supernovae and supernova remnants have the potential to be of great benefit in interpreting astronomical observations, particularly when coupled with computational modeling of the same phenomena.
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From page 135... ...
In many cases, most of the advantage gained by going into a low Earth orbit could be achieved at far less cost with balloons capable of remaining aloft for periods of 100 days or more. Examples of the kind of science that can be carried out with balloons include searches for planets with a coronagraph on a diffraction-limited telescope a few meters in diameter, imaging convective flows and magnetic fields in the Sun's photosphere with a large solar telescope, extragalactic observations with a moderate-sized far-infrared telescope, or all-sky surveys at hard x-ray wavelengths.
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Furthermore, the committee has recommended that the National Virtual Observatory and the National Theory Postdoctoral Program be jointly funded by NASA and the NSF. In addition to NASA and the NSF, DOE participates in astrophysics to address fundamental problems linked especially to particle physics, nuclear physics, and cosmology.
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