Astronomy and Astrophysics in the New Millennium (2001) / Chapter Skim
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2. The Science Behind the Recommendations
2. The Science Behind the Recommendations
Pages 51-94
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- ~ I, The Science 13eh~n] the Recommendations
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All these observations can be interpreted in terms of the inflationary Big Bang theory, which describes how the universe has evolved since the first 10-36 seconds of cosmic time. It is impossible to predict where astronomy will be in the year 3000 AD.
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It is remarkable that the laws of physics developed on Earth appear to be consistent with phenomena occurring billions of light-years away and under conditions far more extreme than those for which the laws were derived and tested. However, researchers have only begun to probe the conditions near the event horizons of black holes or in the very early universe, where the tests of the laws of physics will be much more stringent and where new physical processes may be revealed that shed light on the unification of the forces and particles of nature.
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Understanding black holes Studying star formation and planets Con-X, GLAST, LISA, EXIST, ARISE NGST, GSMT, EVLA, LSST, TPF, SAFIR, TSIP, CARMA, SPST (ALMA, SIM, SIRTF, SOFIA) Understanding the effects LSST, AST, SDO, FASR GLAST of the astronomical environment on Earth Con-X, EVLA, SAFIR, GLAST, LISA, EXIST, SPST EVLA, LSST, VERITAS, SAFIR AST, SDO, Con-X, EXIST NOTE: Acronyms are defined in the appendix.
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From page 55... ...
Its mass is at least half that of Jupiter, the largest planet in the solar system, but its orbit is only one-tenth as large as that of the innermost planet, Mercury (Figure 2.13. Further discoveries indicate that such "hot Jupiters" gas giant planets orbiting 100 times closer to the host star than their analogs in our own solar system are surprisingly common, being found around a few percent of all solar-type stars.
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From page 56... ...
. Reprinted by permission from Nature 378:355-359, copyright 1995 Macmillan Magazines Ltd.
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Now do companion stars affect planet formation? Most stars form in large clusters containing massive stars, such as the cluster associated with the Trapezium in Orion.
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The Kuiper Belt consists of a ring or disk of subplanetary bodies circling the Sun beyond Neptune. Some 200 Kuiper Belt objects (KBOs)
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The rapidity oftheir destruction may interrupt planet formation in these disks. Courtesy of C.R.
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Observations with LEST should increase the number of known KBOs to 10,000, permitting intensive investigation ofthe dynamical structure imprinted on this fossil protoplanetary disk bythe formation process. Courtesy of D.Jewitt (University of Hawaii)
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Courtesy of the W.M. Keck Observatory Adaptive Optics Team.
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62 FIGURE 2.5 The impact of fragment "G" of Comet ShoemakerLevy 9 onto Jupiter in July 1 994 left dark rings of substantially altered atmosphere (lower left section of the planet)
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The mass of a star is the primary determinant of its characteristics over most of its life, yet researchers do not know what determines the star's birth mass. There are many other important unsolved problems in star formation as well, including understanding how molecular clouds form in the interstellar medium, how these clouds evolve to form protostellar cores, what tips the scales in favor of gravitational collapse, what determines when binaries form, how stars form in clusters, and how protostellar winds affect star formation.
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64 ASTRONOMY AND ASTROPHYSICS IN THE NEW MILLENNIUM FIGURE 2.6 Pillars of interstellar gas being eroded by radiation from massive stars in the Eagle Nebula, revealing low-mass stars in the process offormation. HST image courtesy of J
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Magnetic fields play a crucial role in astrophysical phenomena ranging 65
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AST is designed to achieve this angular resolution. With the collecting area of a 4-m mirror, it will also have sufficient sensitivity to measure weak magnetic fields on this scale at the requisite time resolution.
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THE SCIENCE BEHIND THE RECOMMENDATIONS 67 FIGURE 2.7 An image of the full disk of the Sun at x-ray wavelengths (0.0171 ~m) , which are sensitive to the emission from a highly ionized iron atom (eight electrons removed)
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The ejected gas, mixed with the local interstellar medium, can then be recycled to form new stars and planetary systems. Left behind is a compact stellar remnant a white dwarf, with a radius 100 times smaller than that of the Sun; a neutron star, with a radius 1,000 times smaller; or a black hole, with an effective radius that, for a mass comparable to that of a neutron star, is several times smaller yet.
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This image shows the ejected gas, enriched in elements such as carbon by the nucleosynthesis that occurred in the parent star, as it travels outward into the interstellar medium to be incorporated eventually into new stars and planets. The Hubble image was obtained by J.P Harrington and KJ.
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go ASK AS~O~1~ ~ ~~ HOURS 79 To supernova remnants observed by the Chandler X-~ Obse~o~. On the leR ~ an x-r~ color image of Cas~ope~ A, the remnant of a supernova that exploded about 100 yea Do.
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' ' ':':2:2:': :':2:.:2:2::: :2:2: :,:.:,:.:,:,:.: :-:::::::::;~:::::::::::::::::::::: : :.: :,:,:,:,:.:~.y.:,:.: :,:: - - -,:,:: :,:,:,: :.:,:.:.: ............ ''' '.'.'.'.2.2 it .2-2222 2~2~ e2e2~2~yj~;S stellar remnant a neutron star or black hole left behind by the explosion.
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These objects provide laboratories in which matter can be studied under extreme conditions that cannot be duplicated on Earth. For example, the past decade saw the discovery of the theoretically predicted "magnetars," which are neutron stars with magnetic fields 100 times that of normal neutron stars and a billion times that of the largest static fields in the laboratory.
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Many galaxies, including our own, harbor supermassive black holes in their nuclei, and these will almost certainly have an important role in galactic evolution. Finally, in most galaxies there is a significant amount of gas and dust between the stars, out of which new stars continue to form.
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Astronomers are also able to study galaxies at high redshifts by taking advantage of the sensitivity and angular resolution available with the Hubble Space Telescope (HST)
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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.
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has a cosmological constant so that only 30 percent of the critical density is in matter. At the time of the Big Bang, the age of the universe was zero, and the redshift (z)
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The high angular resolution available with GSMT means that it will be able to obtain the spectra of individual stars close to the nuclei of the Milky Way's nearest large companion galaxies, M31 and M32 (Figure 2.131. EVOLUTION OF THE INTERSTELLAR MEDIUM IN GALAXI ES The interstellar medium in a galaxy controls the rate of star formation and thus the evolution of the galaxy itself.
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This image comes from photographic plates taken with the 0.6-m Burrell Schmidttelescope oftheWarner end Swasey Observatory of Case Western Reserve University. GSMT will be able to study individual stars nearAndromeda's center, which is a very tightly packed star cluster not visible in this saturated image.
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All this gas is permeated by cosmic rays, particles moving almost at the speed of light, and by magnetic fields. The primary hindrance to a greater understanding of how the interstellar medium mediates the evolution of galaxies is ignorance of the spatial distribution of these various components of the interstellar medium and how they are interrelated.
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ARISE has the power to study the water emission in other galactic nuclei to search for black holes and determine their mass and the characteristics of the accreting gas.
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Since all the mass must be within the inner boundary of the molecular disk of about 0.13 pc, this mass is probably in the form of a supermassive black hole. The bottom panel shows on a larger scale the synchrotron emission that arises from relativistic electrons ejected along the spin axis ofthe black hole.
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Furthermore, by observing the spectrum of hot gas as it disappears into supermassive black holes, Constellation-X will provide a laboratory for studying the physical processes occurring near the event horizons of black holes under conditions that differ substantially from those near stellar-mass black holes. In a tremendously scaled-up version of the process of mass ejection from disks around protostars, massive black holes not only accrete material but also eject from their vicinity powerful jets at nearly the speed of light (Figure 2.1 61.
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Further discussion of what scientists can learn about black holes can be found in the physics survey report Gravitational Physics: Exploring the Structure of Space and Time (NRC, 19993. Galactic nuclei can become extremely luminous as a result of intense bursts of star formation or the presence of a supermassive black hole.
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Distinguishing starbursts from supermassive black holes is complicated by the fact that AGNs are often shrouded in dust, so that much of the direct emission is hidden from view. Long wavelengths penetrate the dust more readily, so the EVLA, SAFIR, and NGST with an extension into the thermal infrared are all suitable for separating the two phenomena.
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The history of the expansion of the universe depends on the total density of matter in the universe (both ordinary matter and dark matter) and on the possibly non-zero "cosmological constant," which might characterize a sort of "dark energy" in the universe.
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Planned observations of the cosmic microwave background will provide more accurate values of the cosmological parameters, including the density of ordinary matter. This value of the matter density, when compared to an equally precise determination derived from a measurement of the primeval deuterium abundance, will allow a fundamental consistency test of the standard cosmology.
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Surveys under way now, particularly the Sloan Digital Sky Survey, will provide a far more accurate map of the distribution of galaxies in the nearby universe. Direct evidence for the early fluctuations that led to this structure is imprinted on the oldest radiation in the universe, the cosmic microwave background (CMB)
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Gravitational waves excited during the first instants after the Big Bang should have produced effects that polarized the background radiation. More precise measureFIGURE 2.17 The COBE satellite detected tiny variations in the intensity ofthe cosmic microwave background.
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18 The spectrum ofthe primordial sound produced by the Big Bang. The sound waves can be observed through the fluctuations they produce in the temperature ofthe cosmic microwave background.
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Although the uncertainty in their mass makes it difficult to determine exactly how much, astrophysical observations suggest that neutrinos do not account for the bulk of the dark matter. The rest is believed to be in the form of dark matter particles or objects that move relatively slowly, and are therefore called "cold" dark matter.
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The otherthird is in the form of matter,the bulk of which is dark and which scientists believe is composed of slowly moving elementary particles (cold dark matter) remaining from the earliest moments after the birth of the universe.
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As yet it is unclear how much MACHOs contribute to the dark matter in the Galaxy. If MACHOs are made of ordinary matter, then they cannot account for the bulk of the dark matter known to exist in the universe or even in our own galaxy.
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The existence of the neutralino is a prediction of superstring theory, a bold and promising attempt to unify gravity with the other forces of nature. The discovery that neutralinos or anions are the dark matter that binds our own galaxy would shed light not only on the astrophysical dark matter problem, but also on the unification of the fundamental forces and particles of nature.
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