The Decade of Discovery in Astronomy and Astrophysics (1991) / Chapter Skim
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2. Science Opportunities
2. Science Opportunities
Pages 28-54
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From page 28... ...
We have witnessed stars in the act of formation, still wrapped in the gas and the dust out of which they condensed. We have seen other stars exploding, having first spent their nuclear fuel and then collapsing under their own weight.
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From page 29... ...
Kant suggested that a primitive gaseous cloud slowly contracted under the inward pull of its own gravity. The central, densest regions formed the sun.
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Astronomers using arrays of millimeter wavelength telescopes linked together to act as a single large telescope demonstrated that the material around the young stars was in orbit around the stars and was present in a quantity sufficient to make solar systems. IRAS found supporting evidence for a later phase in the life history of solar systems when it discovered that as many as one-quarter of all nearby stars are surrounded by disks of orbiting particles that may be the debris left over from the formation of planets (Plate 2.1~.
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From page 31... ...
At the distance of Alpha Centauri this shift in position amounts to a shift in angle of only a few thousandths of an arcsecond for a planet the size of Jupiter. Yet optical and infrared telescopes linked together as ground- or space-based interferometers will be capable of measuring such small angles and of surveying hundreds of stars within 500 light-years for the presence of distant planets like our own Jupiter.
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From page 32... ...
Flyby spacecraft, observatories on the ground such as the MMA and new 8-mdiameter optical and infrared telescopes, in airplanes such as the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA) , and in orbit about the earth such as SIRTF will determine the size, distribution, and composition of comets as far away as the orbit of Jupiter.
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From page 33... ...
The sun is a great ball of hot gas, about a million miles in diameter. According to modern theory, its central density is about 100 times that of water, and the temperature is about 15 million degrees Celsius.
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From page 34... ...
The number of subatomic particles called neutrinos emitted by the sun and detected on the earth is much smaller than predicted. Neutrinos are produced in nuclear reactions at the center of the sun, and their rate of production has been calculated from our theories of nuclear physics and presumed knowledge of the conditions of temperature and density in the sun.
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From page 35... ...
Because the earliest stages of star formation occur within very dense clouds of gas, impenetrable to visible light, clues must be sought in the radio waves and infrared radiation that can escape the thick clouds (Plate 2.74. During the 1990s, star formation will be a major focus of study with many of the telescopes proposed in Chapter 1, including SIRTF, SOFIA, the MMA, and the infraredoptimized 8-m telescope on Mauna Kea.
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From page 36... ...
Furthermore, that star can spin very rapidly, between 1 and 1,000 revolutions per second; it can anchor magnetic fields that are trillions of times stronger than the earth's, and it can produce periodic pulses of intense radio waves. White dwarfs and neutron stars support themselves against further collapse by the resistance of their subatomic particles to being squeezed more closely together.
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From page 37... ...
The intense bursts of radiation given off by magnetized, rapidly rotating neutron stars are often detected by radio telescopes as pulsars. Stellar black holes are inferred to exist from the x-ray emission seen from some binary stars.
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From page 38... ...
Scrutiny of the x-rays and gamma rays emitted by supernova remnants will help identify the various kinds and proportions of atoms dispersed in supernovae (Plate 2.104. Such a task will be on the dockets of the Gamma Ray Observatory; an Explorer satellite equipped with a gamma-ray spectrometer; AXAF; and two ultraviolet instruments currently under construction, the Far Ultraviolet Spectroscopy Explorer (FUSE)
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From page 39... ...
For example, some observational evidence suggests a systematic color change of galaxies with age, as theoretically predicted. For the l990s, astronomers are building several large, visible-light and infrared telescopes with diameters ranging from more than 300 in.
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Astronomers theorize that quasars constituted the central regions of some galaxies at a very early stage of their evolution. The new generation of large, visible-light and infrared telescopes and the already launched Hubble Space Telescope may be able to detect the weak light of infant galaxies harboring quasars and to advance the study of the connection between quasars and galaxies.
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From page 41... ...
Hints of these effects have also been found in a number of nearby galaxies, and the Hubble Space Telescope will look at a larger sample of more distant galaxies. Black holes might also be indirectly identified by the high-energy emission of the surrounding gas.
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From page 42... ...
Ground-based telescopes may have found gamma rays of extremely high energy coming from astrophysical objects: pulsars, x-ray binary stars, and black hole candidates. The gamma rays are detected by light or particles produced in showers when the gamma rays enter the earth's atmosphere.
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From page 43... ...
The telescopes of the 1990s may change this state of affairs. A number of telescopes, including the ground-based 8- and 10-m telescopes, the orbiting Hubble Space Telescope with its infrared camera, and SIRTF, will all survey the sky for the faint wisps of light emitted by the first generation of stars forming in infant galaxies.
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From page 44... ...
At that time, the enormously hot energy of the cosmic fireball dominated the mass of the universe. Imprinted on this cosmic background radiation should be a record of the distribution of cosmic matter at that time, well before the epoch of galaxy formation.
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Thus with two totally different methods, one using the outward motions of galaxies and the other using the rocks underfoot, scientists have derived roughly similar ages for the universe. This success has been a powerful argument in favor of the Big Bang model.
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From page 46... ...
The most precise measurements of the cosmic background radiation have come from the COBE satellite, which has confirmed that the spectrum of the cosmic background radiation is extraordinarily close to that predicted by the Big Bang model. According to the Big Bang model, hydrogen, helium, and some of the light elements, as well as the cosmic background radiation, were all created in the universe long ago, when the universe was very different from what it is
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From page 47... ...
At an even earlier time, each proton and neutron disintegrates into elementary particles called quarks. The universe becomes a roiling sea of subatomic particles.
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From page 48... ...
Such surveys could be accomplished with moderate-sized visible-light and infrared telescopes. If in the future we find filaments and bubbles and voids with sizes of a few billion light-years, several times larger than those now mapped, then there would be a direct contradiction with the uniformity of matter implied by the cosmic background radiation.
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From page 49... ...
Does it consist of numerous dark objects, like dim red stars, planets, or black holes, or does it consist of subatomic particles that interact with other matter only through gravity? Dark matter could alter our theories of the formation of galaxies or of subatomic particles.
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From page 50... ...
In the coming decade, the gravitational-lens phenomenon will be used as a powerful tool to uncover the nature of dark matter. Alternatively, dark matter could consist of individual, freely roaming subatomic particles, rather than aggregates of particles such as planets.
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From page 51... ...
The essential feature of the inflationary universe model is that, shortly after the Big Bang, the infant universe went through a brief and extremely rapid expansion, after which it returned to the more leisurely rate of expansion of the standard Big Bang model. By the time the universe was a tiny fraction, perhaps 10-32, of a second old, the period of rapid expansion, or inflation, was over.
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From page 52... ...
The universe may expand forever, with its outward motion always overwhelming the inward pull of gravity, in the way that a rock thrown upward with sufficient speed will escape the gravity of the earth and keep traveling forever. Such a universe is called an open universe.
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From page 53... ...
Accurate determinations of distances to galaxies are needed for both of these measurements. One possible means of accurately determining distance involves the scattering of the cosmic background radiation by hot gas in clusters of galaxies by a process called the Sunyaev-Zeldovich effect.
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From page 54... ...
Advocates of the inflationary universe model must hypothesize that space contains yet 10 times more mass not only unseen but undetected and composed of some exotic species of matter. As mentioned earlier, some candidate particles will be searched for in the laboratory using "dark matter" detectors currently under development.
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