Astronomy and Astrophysics Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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4. New Initiatives
4. New Initiatives
Pages 36-66
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From page 36... ...
New phenomena have been revealed at each advance in sensitivity, spectrum coverage, and angular resolution. Increasingly, the complementarily of observations in different parts of the spectrum has been revealed, emphasizing the view that access across the electromagnetic spectrum is essential in advancing our knowledge of the universe.
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From page 37... ...
This can be achieved directly by increasing the diameter of the telescope reflector, or indirectly by coupling together radiation or signals from widely spaced reflectors. To overcome quantum noise we need to provide telescopes with larger collecting areas.
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From page 38... ...
Except for technical details, none of them fundamental, the concept of aperture synthesis carries over to the shorter wavelengths of the
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From page 39... ...
A workshop held in Cambridge, Massachusetts, in October 1985 reviewed the prospects for interferometry and concluded that "imaging interferometry in space will ultimately play a central role in astrophysics, a role comparable in significance to that played by space observations at x-ray and infrared wavelengths." The current level of effort in space interferometry is extremely small, and the workshop concluded that an orderly program had to be constructed. This would have to include the following: technological development of structures, spacecraft control, and optical technology; the study of a variety of instrumental concepts; the flight of small interferometers; and the formulation of a longrange program leading to a major observatory-cIass instrument.
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From page 40... ...
The quasar/active galactic nucleus problem can be used as an illustrative example. These are probably related phenomena, differing only in scale: our own galaxy has a moderately active, compact nucleus, possibly containing a black hole of perhaps a million solar masses.
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From page 41... ...
actually a black hole or is a still more exotic form of matter cannot be said, but it is clear that in studying this class of phenomena we would be drawn into a new domain of physics: the regime of strong-field gravitation.
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From page 42... ...
I ON ~B ROAD L I NE RED 1 ON H.. ~ JO H_ TtIICK DISr ~4 ._ qO 1/2 / / / / / / / / _ / / / / / / / / / /ACCRETION / / / / / / / / ~ ~ / //// = /~//////// / / / / / / / /~ / / / / / / / / / / / / / / / /~;'c~// / / / // / / // // /// / /~/ //// /////////// it, , 1 , , , , 1 1 1 1 1 1 , , , , 1 , , , , 1 , , , , 1 , , , , 1 , , , , 1 , , , , 1 -4 -3.5 -3 -2.5 -2 -1.5 -1 -.5 0 .5 -2 103AU 1 AU ~ ~ / - / / / / / ' so / / / / / / / / / / //~ / / / / / / / / ~ / / / / / DISItS / //// //////// _4 // / _ / / , , Log z FIGURE 4.2 Angular resolution required to study active galactic nuclei.
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From page 43... ...
The mass distribution would be chosen to yield a zero quadrupole moment, thus reducing gravity-gradient torques. The dimensions might well be in the 5~ to 100-m range, and the elements might be 1.5 m in diameter.
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From page 44... ...
44 ,1 1~ ~ _ I: Y it/ It \\ l ,:~41 IN \~\ a\ \\N '\\\\ at\\ V FIGURE 4.3 A (large) space telescope array: Nine 1- to 2-m-class telescopes on a 50- to 100-m tetrahedral truss.
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From page 45... ...
This may be done by using unresolved stars in the wide field of view available to these space interferometers for sensing phasing errors. Optical and infrared interferometry may profit from the extensive phase closure and self-calibration techniques developed for radio aperture-synthesis instruments, and their adaptation must be carefully worked out.
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From page 46... ...
The viewing of the world in Fourier transform space has been a strong current in much of modern science, and over the next 30 years one may well see new possibilities open up as technology advances. Microarcsecond resolution at x-ray wavelengths, for example, would be enormously exciting, and even though x-ray interferometry is a technically difficult concept, there appear to be no fundamental physical barriers.
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From page 47... ...
These observations resulted in maps of galactic sources at resolution down to 1 arcmin at 100 ,um, and detailed spectra of wide classes of astronomical sources. These included regions of star formation, planetary nebulae, highly evolved stars, and external galaxies.
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From page 48... ...
An 8- to 16-m Telescope for Ultraviolet, Optical, and Infrared Wavelengths A large-aperture space telescope for the ultraviolet, optical, and infrared regions has immense scientific potential. The need for such a telescope will be very high after 10 to 20 years of use of HST and ground-based 8- to 10-m-cIass telescopes.
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From page 49... ...
The image is 1/100 arcsec in diameter for a 15-m telescope in visible light. At this resolution the reflected zodical background sky limit is reached at magnitude 33, about 11 magnitudes fainter than ground-based telescopes and 4 magnitudes fainter than the HST.
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From page 50... ...
and studied spectroscopically in the visible with resolutions better than 100 pc for all red shifts, even those greater than 1, limited only by the brightness of the source and the telescope's light-gathering capability. Furthermore, this resolving power allows for direct observations of the superiuminal clouds in sources such as the quasar
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From page 51... ...
They will also be used for spectroscopy of high-surface-brightness regions, again particularly in the nearinfrared region where the resolution gains over the ground-based observations are complemented by a markedly lower background. For galaxies with a bright nucleus, a space-based facility is uniquely suited to determining red shifts, since the optimum aperture dictated by signal-to-noise ratio (S/N)
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From page 52... ...
Stellar Systems. A large space telescope is uniquely suited to stellar astrophysical programs in the ultraviolet.
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From page 53... ...
At resolutions approaching 10 to 40 milliarcsec (wavelength 0.5 to 2 ,um) some of the nearest giants and many more binaries can be resolved by a large space telescope, without the ambiguities associated with the interpretation of speckle interferometry.
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From page 54... ...
It could image and study by spectroscopy the atmospheric composition of not only Jupiterlike but Earthlike planets of nearby stars. It would be possible to search for oxygen, whose presence would be of extraordinary importance; the oxygen and ozone molecules in the terrestrial atmospheres originate in living organisms.
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From page 55... ...
Technological Developments It is clear that meeting the scientific goals outlined here for the use of an 8- to loom telescope will require imaging array detectors of the highest capability in the ultraviolet, optical, and infrared regions. They must have high quantum efficiency, very Tow noise, wide wavelength response, and be packageable into very large mosaic formats without compromising their performance.
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From page 56... ...
. Similar studies of galaxy clusters out to moderate red shifts (Z ~ 0.5)
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From page 57... ...
This could detect stable pulsation periods and thus enable searches for the gravitational waves expected if the sources have very fast millisecond spin periods. High-resolution spectra of QSOs and distant galaxy clusters would measure red shifts directly from their iron-line features as well as probe the internal dynamics of accretion disks and jets where thermal (line)
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From page 58... ...
should have made significant advances in detecting the brightest several hundred sources in the 2~ to 200-keV band by that time, but detailed astrophysical measurements and exploration of the full hard x-ray/soft gamma-ray energy band of about 20 keV to 2 MeV will not yet have been possible. This energy range contains a rich assortment of information that can be used to address each of the field's three major scientific objectives: the early universe, compact objects and stellar collapse, and star formation.
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From page 59... ...
The 50 active galactic nuclei, for which spectra were measured out to about 20 to 50 keV with the HEAO missions, show relatively similar power law spectra with a spectral index of 0.7. If these spectra continue unbroken out to about 1 MeV, the total contribution of all active galactic nuclei would greatly exceed the hard x-ray/soft gammaray background.
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From page 60... ...
Active galactic nuclei, compact objects, explosive phenomena, and the acceleration and interactions of cosmic rays are examples. We must obtain accurate measurements of the gamma-ray luminosity of large numbers of active galactic nuclei so that different production mechanisms can be identified by class and their contribution to the diffuse radiation can be determined accurately.
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From page 61... ...
Nuclear line emission resulting from reactions of energetic particles with the surface material of neutron stars should provide direct information about composition of this material and of surface red shifts from which the massto-radius ratios can be derived. With estimated line fluxes from 10-5 to 10-7 ~ /cm2/s even for relatively nearby objects, substantial sensitivity improvements beyond GRO are required to address these studies satisfactorily.
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From page 62... ...
of galactic sources. It would also dramatically extend the knowledge of high-energy phenomena of active galactic nuclei.
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From page 63... ...
A particular challenge are measurements on a deep-space probe reaching interstellar space outside the heliosphere for detailed in situ investigation of the interstellar medium. Magnet Spectrometer for Particle Astrophysics (ASTROMAG)
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From page 64... ...
Energy Spectra: ~ _ ~ ~1 ~ ~ -c~ O to determine precise energy spectra of cosmic rays over a large energy range in order to understand the processes of particle acceleration on astrophysical scales and of the confinement of cosmic rays to our galaxy. Electrons and Positrons: to measure negative and positive electrons up to energies of a few tesla electron volts.
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From page 65... ...
The deployment of an exceptionally massive array is required in order to study cosmicray particles in the energy range beyond 10~5 eV, where air-shower data suggest a break in the energy spectrum. This break might reflect the large-scale structure of the galaxy and the escape of high-energy cosmic rays from the galactic magnetic fields, or it may signify limitations in the galactic acceleration mechanism.
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From page 66... ...
The ultraheavy isotope measurements are considered in more detail below. For those elements occurring beyond iron and nickel in the periodic table, elemental composition measurements will provide partial information on the nucleosynthesis, acceleration, and transport of ultraheavy cosmic rays in the galaxy.
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