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l
Introduction
OUR COSMIC HERITAGE
Nature offers no greater splendor than the starry sky on a clear,
dark night. Silent, timeless, jeweled with the constellations of
ancient myth and legend, the night sky has inspired wonder
throughout the ages. It is a wonder that leads our imagination
far from the confines of Earth and the pace of present day, out
into boundless space and cosmic time itself.
Astronomy, born in response to that wonder, is sustained by
two of the most fundamental traits of human nature: the need to
explore and the need to understand. Through the interplay of
discovery, the aim of exploration, and analysis, the key to
understanding, answers to questions about the Universe have
been sought since the earliest times, for astronomy is the oldest
of the sciences. Yet it has never been, since its beginnings, more
vigorous or exciting than it is today.
Through modern astronomy, we now know that we are con-
nected to distant space and time not only by our imagination but
also through a common cosmic heritage: the chemical elements
that make up our bodies were created billions of years ago in the
hot interiors of remote and long-vanished stars. Their hydrogen
and helium fuel finally spent,
these giant stars met death in
cataclysmic supernova explosions, scattering afar the atoms of
heavy elements synthesized deep within their cores. Eventually
3
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4
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
this material collected into clouds of gas in interstellar space;
these, in turn, slowly collapsed to give birth to a new genera-
tion of stars. In this way, the Sun and its complement of planets
were formed nearly 5 billion years ago. Drawing upon the ma-
terial gathered from the debris of its stellar ancestors, the planet
Earth provided the conditions that ultimately gave rise to life.
Thus, like every object in the solar system, each living creature
on Earth embodies atoms from distant corners of our Galaxy and
from a past thousands of times more remote than the begin-
nings of human evolution.
Although ours is the only planetary system we know, others
may surround many of the hundreds of billions of stars in our
Galaxy. Elsewhere in the Universe, beings with an intelligence
surpassing our own may also at this moment gaze in wonder at
the night sky, impelled by an even more powerful imagination.
If such beings exist-possibly even communicating across the vast
expanses of interstellar space they, too, must share our cosmic
heritage.
This recognition of our cosmic heritage is a relatively recent
achievement in astronomy. However, it is but one of many such
insights that our generation alone has been privileged to attain.
In all of history, there have been only two periods in which our
view of the Universe has been revolutionized within a single
human lifetime. The first occurred three and a half centuries ago
at the time of Galileo; the second is now under way.
EXPLORATION AND UNDERSTANDING
The discoveries of the past 20 years, made from both ground-
based and space observatories, have radically changed our con-
cepts of the origin and evolution of stars, galaxies, and the
Universe itself.
The 1960's saw the discovery of quasars, x-ray sources outside
the solar system, the cosmic microwave background radiation,
pulsars, high-energy celestial gamma rays, large-scale inhomo-
geneities in the solar corona, and polyatomic molecules in inter-
stellar clouds. The rapid pace of discovery continued in the
1970's:
1970: Uhuru, the first satellite x-ray observatory, is launched; it
reveals that many bright Galactic x-ray sources are neutron stars
accreting matter from nearby companion stars and that many
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Introduction
5
clusters of galaxies are pervaded by hot intergalactic gas whose
mass rivals that of the galaxies themselves.
1971: Using very-long-baseline interferometry (VUBl), radio as-
tronomers find that in a number of quasars, individual radio
components appear to move apart from one another at speeds
greater than that of light; there is still no definitive explanation
for this phenomenon.
1972: The Copernicus satellite is launched to provide high-reso-
lution ultraviolet spectroscopic observations of stars and inter-
stellar gas; vast regions of the interstellar medium are shown to
be heated to hundreds of thousands of degrees by the shock
waves from supernova explosions.
1972: The Gamma Ray Explorer satellite is launched, provid-
ing the first detailed picture of the Galactic plane in gamma rays,
as well as measurements of the spectrum of the diffuse extraga-
lactic gamma radiation; two pulsars are also detected.
1973: Ground-based observations reveal a cloud of sodium gas
surrounding Jupiter's satellite lo; later a torus of gas injected by
lo into orbit around Jupiter is found, presaging the discovery of
Io's vigorous volcanic activity by the Voyager 1 spacecraft.
1973: Observations by the Skylab satellite confirm earlier indi-
cations that high-velocity solar-wind streams flow from "coronal
holes," solar regions of much reduced x-ray and ultraviolet
emission; these streams are later recognized as the source of
many geomagnetic disturbances on the Earth.
1974: Radio observations of the pulsar PSR 1913 + 16 show that
it orbits a companion star every 6 hours; precise measurements
of this binary pulsar later confirm the prediction of the General
Theory of Relativity that a binary-star system radiates energy in
the form of gravitational waves.
1975: Observations confirm theoretical predictions that the so-
lar surface undergoes 5-minute oscillations as a result of waves
in the solar interior; detailed measurements of these oscillations
later provide seismic probes of solar structure that reach nearly
to the Sun's core.
1976: An experiment to measure the flux of neutrinos from the
center of the Sun, in progress since 1970, shows that the flux is
no more than one third of that predicted by current theory; this
finding prompts a searching re-examination of the theory of
generation of nuclear energy in stars.
1977: In the first such discovery since the rings of Saturn were
discovered in the seventeenth century, rings are found around
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
Uranus. In 1979, Voyager 1 detects the first known ring around
Jupiter and in 1980 reveals complex structure in the rings of
Saturn.
1978: The Einstein Observatory, carrying an imaging x-ray tele-
scope, is launched to acquire the first high-resolution images and
detailed spectra of the x-ray sky; these observations provide im-
portant new insights into the properties of nearly every kind of
astronomical object.
1978: Infrared spectroscopy reveals the expansion of a shell of
dust and gas away from a protostellar condensation in the Or-
ion nebula; if the expansion is due to the pressure of radiation
from a newborn star within the shell, this star must be only 2000
years old, and thus the youngest ever observed.
1978: Radio and x-ray emissions from the Galactic object SS 433
prompt optical studies that reveal that it emits jets of matter at
about one fourth of the speed of light; SS 433 may be a small-
scale stellar counterpart of the mysterious objects that produce
energetic jets in some quasars.
1978: The International Ultraviolet Explorer (lUE) satellite is
launched; observations establish temperature scales for hot stars,
reveal resemblances between quasars and Seyfert galaxies, and
show that mass loss from stars at rates high enough to affect
stellar evolution is nearly universal.
1979: Isotopic analysis of cosmic rays shows conclusively that
they constitute a sample of matter with a nucleosynthetic his-
tory different from that of the Sun.
1979: The most intense gamma-ray burst ever recorded is ob-
served by an international network of spacecraft; it is shown to
have come from the same direction as that of a supernova rem-
nant in the Large Magellanic Cloud.
1979: A multiple quasar is detected and shown to be the re-
sult of the splitting of light beams from a single, distant quasar
by the "gravitational lens" effect of an intervening galaxy; a
second example is found in 1980.
These and other key discoveries of the past 20 years must
certainly be ranked in significance with those in the decades
following Galileo's telescopic observations. They are the direct
results of the imaginative application of new technologies for
obtaining and recording astronomical information. Indeed, the pace
of discovery has been set largely by the rate of advance of
technology.
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Introduction
7
During the 1970's, for example, the maturing of space tech-
nology and instrumentation opened up the far-ultraviolet, x-ray,
and gamma-ray regions of the spectrum to extensive new obser-
vations. Infrared astronomy from the ground and from aircraft
and balloons made major strides, with orbiting telescopes sched-
uled for the decade ahead. The development of highly efficient
detectors for optical astronomy permitted the study of extremely
faint and previously inaccessible objects with large telescopes and
enabled smaller facilities to become major research tools. New
technologies for telescope construction employing thin mirrors or
mirror segments, ultrashort focal lengths, lightweight support
structures, and innovative designs for domes or housings-made
it both technically and economically feasible to build much larger
telescopes for optical and infrared studies. Computers evolved into
workaday tools in both the laboratory and the observatory so that
it is now feasible to apply them to data reduction, image pro-
cessing, and theoretical studies in research facilities across the
nation.
The 1980's will almost certainly witness further discoveries to
rank with those of recent decades; however, new discoveries do
not necessarily lead immediately to a deeper understanding of the
Universe. Such understanding, the ultimate goal of astronomy,
requires the careful analysis of observations to test their validity
and to assess their relationship to currently accepted knowledge.
In contrast to observational discoveries, major advances in our
understanding of the Universe seldom burst suddenly upon the
scientific world, bearing key dates that will ring through his-
tory. Rather, they usually require the systematic measurement,
classification, interpretation, and study of many objects and
phenomena, whose common properties and unifying features may
not become apparent until years of effort have been devoted to
the task. Our empirical knowledge of the Universe is gained al-
most entirely from the laborious, time-consuming collection of the
feeble electromagnetic radiations that reach us from very distant
objects. Instruments and facilities to follow up and analyze ini-
tial discoveries must therefore be more powerful, more versatile,
and longer lived than those intended primarily for discovery.
They must also be able to return and process new information at
more rapid rates, if advances in our understanding are not to lag
behind the pace of initial exploration.
The gathering of observational data is, however, only the first
step in the quest for understanding; these data must then be
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
analyzed and interpreted with the aid of astrophysical theory. The
task of theory is to develop physical models for the mecha-
nisms that underlie the observed phenomena, to calculate the
properties of the models, to test these properties through com-
parisons with the observations, and to predict the results of new
observations. When such comparisons are favorable and the pre-
dictions accurate, our understanding has advanced. The con-
struction of astrophysical theories is based on the results from
mathematics and the other sciences, particularly physics and
chemistry. Laboratory studies are essential to provide the atomic,
molecular, and nuclear data needed in theoretical analysis. All of
these activities essential to the search for understanding are
nurtured in our universities and research institutions, where the
astronomical knowledge and skills gained in the past are refined
by new research results and transmitted to those who will fol-
low.
The past decade has seen impressive progress toward under-
standing many of the more significant and challenging problems
of contemporary astronomy. For example, in the decade be-
tween the launch of the Uhuru satellite in 1970 and the imaging
and spectroscopic work of the Einstein Observatory, - x-ray as-
tronomy progressed from a low-resolution survey of the x-ray sky
that revealed a few hundred mostly unidentified sources, to the
detailed study of x-ray emission from thousands of astronomical
objects of all classes, ranging from normal stars to quasars and
clusters of galaxies. The model of x-ray stars based on the the
.. . .. . . . . . . .
ory ot accretion ot matter onto compact objects such as neutron
stars and black holes has provided a possible model for also
understanding the vastly more powerful energy sources of ac-
tive galactic nuclei and quasars.
Another example of impressive progress recorded during the
1970's is our increased understanding of the structure and en-
ergy balance of the interstellar medium. Ultraviolet spectroscopy
provided by the Copernicus and JUE satellite observatories, cou-
pled with x-ray observations from rockets and satellites, has re-
vealed that large regions of interstellar space are filled with gas
heated to hundreds of thousands of degrees by shock waves from
supernova explosions; other ultraviolet studies have shown that
mass loss is a feature of normal stellar evolution. These investi-
gations, powerfully aided by theoretical and laboratory studies of
atomic and molecular properties, have led to a new understand
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Introduction
9
ing of the ways in which stars are coupled to their surrounding
environment.
In some important areas of astronomy, however, understand-
ing has progressed less rapidly, often because critical observa-
tions needed to distinguish between alternative theoretical possi-
bilities are lacking. One such area is star formation, now known
to be occurring in certain regions of the disks of many galaxies,
including our own. The phenomena involved are extremely
complex. Stars are born in clouds of gas and dust that form at
low temperatures and radiate predominantly in the infrared and
millimeter wavelength regions of the spectrum. Despite the great
improvements in detectors and ground-based instrumentation in
these wavelength regions during the 1970's, a new generation of
observational facilities both in space and on the ground will be
required to furnish the increases in spatial and spectral resolu-
tion needed for detailed comparison of regions of star formation
with increasingly sophisticated theoretical models.
The evolution of galaxies is another area in which our under-
standing has been impeded by the lack of observations of suffi-
cient numbers of objects at or beyond the limits of present fa-
cilities, although the 1970's provided fascinating hints of what we
will eventually find. The 1960's furnished clear evidence that we
live in an evolving Universe: the detection of the cosmic micro-
wave background radiation, believed to be a relic of the big bang,
and the discovery that the densities of radio sources and qua-
sars increase with distance as one looks back to earlier stages in
the history of the Universe. Recent observations suggest that
distant galaxies are bluer than nearby ones, providing the first
direct evidence for the evolution of galaxies. A better under-
standing of the evolution of the Universe will require measure-
ments of much more distant and hence much fainter galaxies than
are currently observable with our largest telescopes equipped with
the best detectors. Only through such measurements will we be
able to determine the general properties of galaxies at early stages
in their evolution, when these properties were noticeably differ-
ent from those of galaxies closer to us.
A DECADE OF OPPORTUNITY
The Astronomy Survey Committee believes that the programs
recommended in this report are those that will most effectively
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10
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
advance both exploration and understanding during the coming
decade.
These programs address the most significant questions that
confront contemporary astronomy. For example: What is the large-
scale structure of the Universe? How do galaxies evolve? What
role do violent events play in the evolution of the Universe? How
are stars and planets formed? What causes activity on the sur-
faces of the Sun and other stars? How widespread are life and
intelligence in the Universe? And do the connections between
astronomy and the nature of the fundamental forces hold the key
to a unified understanding of all cosmic processes? Chapter 3
presents a detailed examination of these questions and a discus-
sion of how they may be addressed through implementation of
the Committee recommendations.
The technological developments of the 1970's permit these
problems to be attacked now, with a high degree of effective-
ness, and at reasonable cost. The maturing of space astronomy,
advances in detectors, reduction in cost of computers, and new
technologies for constructing telescopes have already been men-
tioned; to these developments must be added more specialized
advances, such as the refinement of radio Vim; short-wave-
length antenna design and fabrication; new approaches to the
detection of cosmic rays, neutrinos, and gravitational waves; and
infrared interferometry. New facilities incorporating these devel-
opments will undoubtedly yield advances in our understanding
of the Universe and, like those of the recent past, will produce
additional new discoveries of their own.
One should also recognize the importance of astronomical re-
search as an essential contribution to the scientific and techno-
logical vigor of the nation. The entire field has grown explo-
sively during the past two decades, and the research activity of
trained astronomers has become a significant component of the
U. S. scientific enterprise. Maintaining U. S. leadership in astro-
nomical research will be an increasing challenge during the 1980's,
as other nations continue to develop their scientific capabilities.
Research in astronomy has furthermore often had a surprising
impact on technology. It was through attempts to understand the
orbiting of the Moon and planets that Newton discovered the
laws of motion that are the basis of modern engineering. The
theory of radiative transfer, the development of which was
stimulated by the need of astrophysicists to understand the es-
cape of radiation from the outer layers of a star, was later ap
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Introduction
11
plied by engineers to studies of the escape of neutrons from
nuclear reactors. In attempting to explain the source of stellar
energy, astrophysicists helped to advance our understanding of
thermonuclear fusion; astrophysical studies of plasmas in space
have contributed to the theory of magnetic plasma confinement,
which is applied to the control of thermonuclear fusion for
practical purposes.
New concepts emerge as astronomy attempts to understand the
Universe. Picked up and developed by other scientists, they be-
come part of the knowledge that underlies modern technology.
Today astronomers are again confronted by puzzling phenomena
in space, such as relativistic beams of matter, interstellar ma-
sers, and superdense matter. The new concepts that will be re-
quired to understand such phenomena will surely have an im-
pact on the technology of the future.
The programs recommended are those that the Committee be-
iieves are most likely to promote scientific knowledge in the
coming decade. However, no projections for a decade of re-
search can be exhaustive, particularly for an age of discovery like
the one in which we live. A different and still more wonderful
view of the cosmos will almost surely be revealed to us in the
years ahead. The discoveries of our generation have brought us
to the threshold of a revolution in physical thought, in which the
properties of elementary particles may hold the key to under-
standing the early history of the Universe and in which the
quantum properties of gravitation, unrecognized in the theories
of Newton and Einstein, may play a central role in understand-
ing cosmic evolution. Flexibility and openness to new opportu-
nities, as well as implementation of the programs recommended
here, will be needed to respond effectively to discoveries and
developments that cannot now be foreseen.
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A 2-,um infrared image of the center of the Galaxy, hidden
by 30 magnitudes of optical extinction. (Photo courtesy of G.
Neugebauer and E. Becklin, California Institute of
TechnologyJ
Representative terms from entire chapter:
interstellar space
