|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 262
262
4. Subject to periodic review, long-term support
should be provided to strengthen existing centers to
ensure that laboratory astrophysics is a major influen-
tial part of research.
5. Funding agencies should encourage the convening of
workshops attended by astronomers and by laboratory astro-
physicists to ensure that the astronomical needs are
recognized.
6. A number of visiting fellowships should be created
to encourage astronomers and laboratory astrophysicists
to visit institutions where research relevant to astronomy
can be pursued.
7. Support should be maintained for data centers to
provide critical compilations and assessments of the
basic physical data required in quantitative applications.
I I . THEORETICAL ASTROPHYSICS
A. The Nature and Role of Theory in Astrophysics
The relationship between theory and observation in astron-
omy is complex and symbiotic, and it must be examined with
care if resources are to be distributed wisely. In a fun-
damental sense, observation is the prime mover of the re-
lationship. Without observational input, theory can say
nothing about what actually is; it can only explore the
multitudinous possibilities of what logically might be.
No theoretical astronomer, however abstract in orienta-
tion, would seriously dispute that the ultimate goal of
astronomy is to understand the Universe.
It should be equally apparent that observations without
theoretical input can at best yield a superficial view of
the cosmos. Real understanding can only occur when the
observational information is incorporated into a concep-
tual framework of unifying principles. A healthy science
is characterized by the intertwined and parallel develop-
ment of new concepts as new information is gathered.
Attempts to place in order of priority the support of
theory and the construction of new observational facil-
ities create an artificial and misleading dichotomy.
Theoretical astrophysics resists easy characterization.
It spans a broad range of activities, from the interpreta-
tion of observations to the development of new concepts.
Theory unifies the science by revealing underlying connec-
tions between seemingly diverse phenomena. For example,
in the past decade we have learned that the gaps in the
OCR for page 263
263
ring systems of planets are created by resonances similar
to those responsible for spiral structure in galaxies.
We have also seen the emergence of the concept of the
accretion disk for the construction of models of cata-
clysmic variables, binary x-ray sources, the nuclei of
active galaxies and quasars, and the origin of planetary
systems.
Theory links astronomy to other branches of science.
In the past decade we have witnessed the incorporation of
a large body of chemistry into astronomy, revealing con-
nections between planetary atmospheres, comets, and inter-
stellar gas clouds and showing how laboratory measurements
and theoretical calculations can be combined with radio-
astronomy observations to infer the physical conditions
m e relationship is often
in regions of star formation.
reciprocal: astronomical observations have provided
information on atomic and molecular processes that has
not been obtained experimentally and indeed have dis-
covered molecules never seen in the laboratory. There
are many such relationships: nuclear matter theory and
low-temperature physics and the structure and formation
of neutron stars, particle physics and cosmology, and
controlled thermonuclear fusion research and spectral
. . ~
-
observations of cosmic x-ray sources, to name a few.
Others may emerge in the next decade, for example, the
link between solar-system plasma physics and macnetohYdro-
dynamics and the study of similar phenomena in active
stars and galaxies, which is at present tenuous, will
probably be strengthened.
As observational techniques become more diverse and
sophisticated, the demands on theory increase. Thus
advances in radio, optical, and x-ray astronomy have
yielded a growing body of evidence for well-collimated
beams of relativistic particles emerging from radio
galaxies and the Galactic binary SS433.
The cause of the
jets and the relationships between the emissions at
different wavelengths and between the different objects
are yet to be recognized.
Sometimes theory leads observations. For example, a
well-developed theory of gravitational radiation was in
place before the discovery of the binary pulsar. After
its detection it was clear immediately that detailed
observations of the pulse-arrival times could provide
constraints on the nature of the system, as well as
confirmation of the theory of gravitational radiation and
information on possible alternatives to the general
theory of relativity. Entire areas of astrophysics can
OCR for page 264
264
come into existence without a specific observational
reason, but because astronomers work out the consequences
of what is already known. The concept of the black hole
is an excellent example. It would not be worth taking
seriously if it were only an ad hoc hypothesis, advanced
to explain the peculiarities of Cygnus X-1. What gives
compelling intellectual force to the concept is its under-
lying basis of well-developed theories of general relativ-
ity, steller evolution, and the equation of state of mat-
ter at high densities, whose development long preceded the
observational discovery of the first black hole candidate
objects. Neutron stars were likewise preconceived.
An important role of theory is the generation of such
concepts or paradigms, which have great intrinsic value
even in the absence of an observational basis. A marvel
of recent astronomy is the frequency with which these are
reflected in nature. Although evidence for their reality
is usually found by chance, the theoretical concepts spur
new observational programs and provide a focus for further
development once a phenomenon is discovered. Other para-
digms exist, such as stars powered by accretion onto a
neutron star core and the radiative decay of low-mass
black holes, which are not strongly indicated by present
observations but which we believe to be important issues
for the next decade.
Often theory lags observations. Then the observations
must await theoretical insight to realize their full
value. For example, a wealth of data on the distribution
of galaxies in the sky has existed for many years, but
until recently its meaning remained obscure. The new
discoveries only occurred with the development of a power-
ful and different point of view. A triumph of the 1970's
was the analysis of these data in terms of correlation
functions' which revealed a power-law spectrum of fluc-
tuations that may have deep cosmological significance.
Such theoretical insights not only enhance the meaning of
existing observations, they drive new observational
programs--in the case of galaxy clustering, systematic
red-shift surveys.
Theoretical knowledge is "consumed" by observational
advances, which often exhaust the power of a theoretical
concept to accommodate them.
For example, it became
apparent in the 1970's that the enormously successful
theory of the solar wind was inadequate to deal with the
complex variations observed in the x-ray brightness of
the corona and in the flow velocities and magnetic fields
of the wind. Some new ingredient--the concept of coronal
OCR for page 265
265
holes--needed to be incorporated into the theory. As
another example, it appears today that the theory of the
electrodynamics of neutron stars is inadequate to explain
the inner structure of radio pulsations and that a vital
ingredient is lacking.
The discovery of an unexpected phenomenon is usually
followed by a period of model building--attempts by
observers and theorists to fit the phenomenon into the
existing conceptual framework. Elaborations are usually
carried out by theorists who have a responsibility to
make predictions that can be tested by observations.
Predictions may be most valuable when they fail to be
confirmed by observation. m is has been the case with
the 37C1 solar neutrino experiment, in which the dis-
crepancy between the theoretical predictions and the
initial observations stimulated many careful investiga-
tions of the solar interior and is a powerful motivation
for the development of new detectors of solar neutrinos.
At the time of this writing we are not sure whether the
discrepancy is a fundamental one or whether it is a mat-
ter of details that will soon be resolved. However, we
clearly know much more about the Sun today than we would
have had the theoretical prediction been confirmed by the
first observations.
Another kind of model building involves attempts to
synthesize our understanding of diverse phenomena into
global models. m us we use our knowledge of stellar
evolution, mass loss from stars, supernova explosions,
and interstellar gas dynamics to model our Galaxy as an
ecosystem, in which the observed distributions of stars
and interstellar matter result from cyclic flows of mass
and energy. Understanding our own Galaxy in such a
global sense is a first step toward understanding the
differences among galaxies and unifies galactic and
extragalactic astronomy.
As predicted by the Greenstein report, computers have
played an increasing role in theoretical astrophysics
during the 1970's. We have witnessed the development of
powerful numerical techniques by which we can explore
astronomical phenomena that have long resisted concise
analytical descriptions. Tree outstanding examples come
to mind: many-body codes to simulate the evolution and
interactions of star clusters, galaxies, and clusters of
galaxies; hydrodynamic codes to simulate the formation of
protostars, stellar explosions, and interactions with
interstellar gas; and relativity codes to simulate the
behavior of systems with strong gravitational fields,
OCR for page 266
266
such as collapsing stars. With these codes, theorists
specify hypothetical astrophysical environments and use
computers as laboratories for experiments in astrophysics.
Another vital role of theory is the development of
interpretive tools to translate data into meaningful
information. An obvious example is radiative-transfer
theory, by which a spectrum is transformed into physical
parameters such as velocity, density, temperature, and
chemical composition. Without the theory, a spectrum is
little more than a jumble of photons. Radiative transfer
was once regarded as a mature area of theory, but with the
discovery of new phenomena and the advance of astronomy
into unexplored spectral ranges, it has again become a
rapidly growing and exciting field.
For example, the
advent of ultraviolet spectroscopy made it obvious that
many hot stars were losing mass in powerful supersonic
stellar winds.
Not only the interpretation of the
observed spectra but also the very understanding of the
mass-loss phenomenon require the development of new tech-
niques to describe radiative transfer in differentially
expanding media. The new theoretical principles provide
a common ground for such different phenomena as the sPe
tra of hot stars, supernovae, ana one emission spectra or
quasars. Extensions of radiative transfer theory are also
needed to interpret the observations of maser emission
from interstellar and circumstellar molecules. In the
coming decade further demands will be made on radiative-
transfer theory, particularly as a result of the employ-
ment of powerful spectrometers in the far-infrared, ultra-
violet, x-ray, and gamma-ray bands. The development of
theoretical and computational tools to interpret observa-
tions is an essential part of any observational program
and must be supported even as the telescopes and detectors
are designed.
Another example of a mature but vital field is dynami-
cal astronomy, the study of motions dominated by gravita-
tional force. Although the basic concepts were developed
by scientists such as Newton and Laplace, the field con-
tinues to advance.
Some of the most exciting investiga-
tions of the last decade have been the elucidation of
evidence for unseen matter in galaxies, the formation of
planets from the solar nebula, and solar-system tests of
general relativity. The study of the dynamics of self-
gravitating stellar systems, from globular clusters to
clusters of galaxies, provides an important link between
astrophysics and plasma physics. While substantial
progress has been made in understanding the consequences
OCR for page 267
267
of particle interactions, the elucidation of collective
or collisionless phenomena in these systems remains a
major challenge.
B. Accomplishments of the 1970's
Important theoretical progress was made in a wide range
of areas of astronomy in the 1970's. In this section we
describe a few of the highlights of the past decade. m e
topics are chosen not to provide a comprehensive summary
of the field but rather to exhibit the ways in which theo-
retical research strengthens and advances astronomical
knowledge and the variety of systems on which major
progress has been made.
Galactic Evolution.
Decades from now, the 1970's are
likely to be remembered as a period when the complexity
of galactic evolution was glimpsed for the first time.
Galactic colors and luminosites change as their stellar
populations evolve: galaxies collide, leading to violent
transitory tidal distortions, and coalesce, because the
collisions are inelastic; galaxies may lose all their gas
through ram pressure stripping by the intergalactic med-
ium, but they may also acquire gas from the accretion of
intergalactic clouds. Even the spiral structure in ordi-
nary spiral galaxies causes important secular changes in
the galaxy's mass and angular momentum distribution over
a Hubble time. m e theoretical work on each of these
processes has in turn stimulated new observations and the
reinterpretation of existing observations. we appear tn
be in the midst of a major revolution in our thinking
about galaxies.
.. _ . ., _ ~ ~~` Em. _~
General Relativity. The advances in General Relativity
can be roughly classified as belonging to the strong-field
limit or the weak-field limit. Consider the strong-field
limit first. Black holes began the decade as mathematical
abstraction (an exact solution to the Einstein equations).
By the end of the 1970's we knew with some confidence
that, for example, black holes are dynamically stable and
uniquely described by the Kerr metric, that their colli-
sions produce new black holes and radiate gravitational
waves, and that quantum processes cause very small black
holes to explode into a shower of photons and other par-
ticles. In the weak-field limit the main achievement has
been the high-precision observational verification of the
theory. A variety of new and old solar-system tests,
including the retardation and deflection of radio signals
OCR for page 268
268
plus lunar laser ranging and spacecraft tracking, support
General Relativity as the correct post-Newtonian gravita-
tional theory. Parenthetically, they also demonstrate our
impressive theoretical understanding of nonrelativistic
effects in the solar system: the range residuals in the
tests are typically no more than one part per billion.
The binary pulsar has provided the first test of General
Relativity ever made on an object outside the solar sys-
tem and has provided striking evidence for the existence
of the quadrupole gravitational radiation predicted by
the theory.
Shocks in Interstellar Gas. In the 1970's, observa-
tions in radio, infrared, optical, ultraviolet, and x-ray
astronomy have shown that the interstellar medium is per-
vaded by shocks. These observations have stimulated
extensive development of the theory and consequences of
such shocks; their origin in stellar explosions and stel-
lar winds; the effects of radiative precursors, thermal
conduction, and magnetic fields on their structure; the
roles of shocks in the cycling of the gas between cool
dense phases and a hot tenuous phase, in destroying
interstellar dust grains, and in the acceleration of
cosmic rays. We now appreciate that shocks play a major
role in the cycle of interstellar matter between gas and
stars, and we suspect that they may cause propagating
waves of star formation. Recent studies show the impor-
tance of shocks in dense interstellar clouds. It appears
that they are responsible for the infrared emission from
H2 molecules in the Orion nebula. We are beginning to
understand how such shocks can initiate networks of chem-
ical reactions in the clouds.
Volcanism on Io. One of the most spectacular images
of the 1970's is the Voyager picture of a volcanic plume
rising 200 km above the surface of Jupiter's satellite
Io. The prediction of volcanism on Io, shortly before the
discovery of eight active volcanoes during the Voyager
flyby, is also a spectacular theoretical accomplishment.
The satellite Europa perturbs Io's orbit away from cir-
cularity, so that the Jovian tides on Io are not constant.
The consequent deposition of energy on Io due to the tidal
working of the rock was predicted to be sufficient to heat
all but the outer crust of the satellite to a molten
state.
X-Ray Astronomy. The flood of x-ray observations in
the 1970's offered a difficult challenge and a remarkable
opportunity to theoretical astronomers. As we enter the
1980's we have a broad understanding of the nature and
OCR for page 269
269
origin of the x-ray emission from a wide variety of ob-
jects. Many of the galactic sources were recognized as
close binary systems, with mass flow onto an accretion
disk around a compact object, either a neutron star or a
black hole. The x-ray emitting regions of these sources
are some of the most exotic environments known to physics;
to understand them requires consideration of gas dynamics
and new radiative processes in relativistic flows--for the
case of neutron stars, in magnetic fields greater than
1012 gauss. The x-ray burst phenomenon was interpreted
as thermonuclear explosions on neutron star surfaces. The
need to understand the origin of the x-ray binaries sting
ulated extensive preliminary development of the theory of
the evolution of binary star systems with mass transfer.
These new developments in the "mature" area of stellar
evolution theory have led in turn to a better understand-
ing of novae and cataclysmic variable stars. The efforts
to understand why compact x-ray sources occur so fre-
quently in globular clusters and in galactic nuclei have
led to a better understanding of the dynamical evolution
of dense stellar systems.
Accurate x-ray position deter-
minations were used to determine the masses of x-ray
sources in globular clusters, indicating that the x-ray
sources are low-mass binary systems. There is now little
doubt that the x-ray emission from clusters of galaxies
is due to hot intracluster gas enriched in heavy elements,
and this realization has had a profound impact on our
understanding of galactic evolution in these clusters.
Galaxy Clustering. Detailed statistical analysis of
galaxy catalogs has shown a remarkably simple and regular
clustering structure. It is now widely recognized that
galaxy correlation functions offer us important clues to
conditions in the early universe, and attempts have begun
to exploit these clues. The progress of this field exhib-
its the synergistic relationship of theory and observa-
tion: galaxy catalogs compiled in the 1960's were ex-
ploited by intensive theoretical analysis in the 1970's,
and the results from this analysis stimulated the compila-
tion of extensive new catalogs (including red shifts),
which will be ready early in the 1980's.
Ephemerides. The ephemerides of the Moon and inner-
most planets have improved in accuracy by several orders
of magnitude since the late 1960's. The combination of
vigorous theoretical modeling and precise numerical inte-
gration of the orbits have permitted fits to new data
types with unprecedented accuracy. The range data are
fit with typical accuracies of 0.3 m (lunar laser), 8 m
.
OCR for page 270
270
(Mars Viking), kilometers (Mercury and Venus radar), and
tens of kilometers (Jupiter Pioneer). Optical positions
remain the only data type for Saturn through Pluto and
the smallest bodies of the solar system, while occulta-
tions are important for the Moon. Accurate very-long-
baseline interferometric angular positions exist for
several inner bodies. The future holds the promise of
further improvements in measurement techniques plus the
spread of accurate ranging to more distant bodies. The
solutions with these data permit stringent tests of rela-
tivistic gravitational theories, the determination of
masses and radii, the measurement of catalog errors, and
the determination of rotational variations.
Final Stages of Stellar Evolution. In the 1970's the
evolution of a massive star, from hydrogen burning on the
main sequence to the collapse of the central region to
greater than nuclear density, has been delineated. This
problem was posed in the 1930's, but its solution required
an understanding of neutral current processes in the weak
interaction, detailed knowledge of nucleosynthesis pro-
cesses in stars, and numerical hydrodynamics and stellar
evolution performed by computer. This is leading to a
quantitative understanding of the major features of
observed supernovae in terms of models of an exploding
star and to quantitative examination of the sites of and
yield from stellar nucleosynthesis. For the 1980's many
further problems can be studied, for example, nonspherical
collapse, the continued exploration of possible explosion
mechanisms, and the nature of the gravitational radiation.
Analytical Dynamics. There are still many dynamical
problems that yield to analytical approaches. As an
example it is now known that climatic changes on Mars may
result from large changes in its obliquity brought about
in turn by long-period changes in the orbit. Other prob-
lems have benefited from the development of computer pro-
grams that expand and manipulate long series, most par-
ticularly Poisson series. These programs have generated
analytical theories for the motion of the Moon, planets,
and satellites and for the rotations of the Earth and the
Moon. Such programs are in their infancy, and their
future development and extension to the manipulation of
general orthogonal functions will provide a tool with
broad applications to theoretical astrophysics.
OCR for page 271
271
C. Scientific Questions for the 1980's
Scientific knowledge advances by solving old problems and
by posing new ones. Theory develops best in a spontane-
ous, unpredictable way, and prognostications for its
future development are likely to be misleading. However,
theorists have a responsibility to pose questions that
focus attention on scientific issues. In this spirit we
present, in random order, a list of questions for the next
decade, chosen to illustrate the range and diversity of
the science. We emphasize that this list is not intended
to be complete in any sense. Some of the questions were
apparent a decade ago; some are new. We expect that only
a fraction of them will be answered in the next decade.
Some will remain; others will be revised or replaced by
more manageable subquestions. For many, the answers will
be provided by new observations. And of course, many of
the most important advances in theory will address ques-
tions that we have not yet asked.
How are stars formed, and what processes determine the
initial mass function?
Why are some white dwarf stars strongly magnetized and
others not?
How do accretion disks accrete?
What powers the jets of active galactic nuclei?
Is the solar system stable?
Why is the galaxy correlation function a power law of
slope minus 1.8?
What determined the entropy-to-baryon ratio of the
Universe?
What was the origin of globular clusters, and what
will be their fate?
How are planetary nebulas formed?
What accounts for the apparent deficiency of neutrinos
from the Sun?
Why are Jupiter's outer satellites retrograde?
Where did Pluto come from?
How can some isolated stars be x-ray sources?
Under what circmstances does mixing occur within the
stars?
What accounts for the sunspot cycle?
Why do solar magnetic fields clump to form sunspots?
How did the Kirkwood gaps form?
What accounts for the isotopic anomalies in
meteorites, interstellar gas, and cosmic rays?
What physical processes set the characteristic masses
and radii of galaxies?
OCR for page 272
272
What is the equation of state for dense nuclear matter?
What accelerates cosmic rays, and how do they
propagate?
How should we compute the transport coefficients of
astrophysical plasmas?
How and where are interstellar grains formed?
What powers the winds in the T-Tauri stars?
How much energy is liberated as gravitational
radiation during gravitational collapse?
Why did the quasars appear at z = 3.5, and why are
there practically none left today?
Apart from General Relativity, are any theories of
gravity consistent both with solar-system data and the
observations of the binary pulsar?
What accounts for the break in stellar rotation rate
as a function of spectral type?
How is the energy of a pulsar glitch stored in neutron
star matter, and what determines its release?
What fraction of stars ought to have planets? Earth-
like planets?
How is spiral structure in the galaxies maintained?
What events triggered the formation of the solar
system?
How are power-law spectra produced in quasars?
How are the coronas of the Sun and similar stars
heated?
What role does neutrino pressure play in supernovae?
Can elliptical galaxies be formed from the merging of
spirals?
What is the global nature of convection in stars?
What processes, in stars or elsewhere, have affected
the deuterium abundance of the interstellar medium?
What is the great Red Spot on Jupiter?
What determines the fate of common-envelope binary
stars?
What is the prime mover of active galactic nuclei and
quasars?
Does differential diffusion play a role in determining
stellar surface abundances?
How are interstellar clouds supported against gravita-
tional collapse?
What is the nature and origin of the mass that
surrounds galaxies?
How do pulsars pulse?
Apart from Freidmann models, are there any observa-
tionally viable comological models of the big bang?
OCR for page 275
275
The Panel on Theoretical Astrophysics of the
Greenstein Committee also recommended the following:
The strengthening of theoretical groups at the
National Astronomy Centers (such as Kitt Peak and the
National Radio Astronomy Observatory). These groups have
actually decreased in size. We believe that the need to
. .
implement such a recommendation has become acute (see
Recommendation 2 below).
The establishment of a National Center for Theoretical
Astrophysics, funded at a level of approximately $750,000
per year. This was not done. We do not recommend such a
facility now (see Recommendations 2, 3, and 5 below).
Providing an increase of computer power available to
theorists in the form of an upgraded computing center at
Kitt Peak National Observatory. This was not done. Cur-
rent technology suggests a different solution (see Recom-
mendation 3 below and Chapter 5 of this volume, containing
the report of the Panel on Data Processing and Computa-
tional Facilities).
2. Current Resources for Theoretical Astrophysics
Here we assess the current support pattern and human
resources for theoretical astrophysics.
me quantitative
data presented here are necessarily approximate, as their
estimation requires judgments as to what research programs
or fractions thereof are theory.
Theoretical astrophysics research (excluding solar-
system physics) is currently funded by NSF at a level of
approximately $2.5 million/year (fiscal year 1978) and by
NASA at the level of approximately $1.1 million/year
(fiscal year 1979) through university grants programs.
This funding is provided through approximately 60 grants
by NSF and 30 grants by NASA. In addition to supporting
these explicitly theoretical programs, NASA also supports
a significant amount of interpretive theory related to
specific missions. We have not been able to make a reli-
able quantitative estimate of the level of this support.
Theoretical astrophysics research is also supported by
NSF and NASA through the employment of theorists at
nationally prominent centers of astronomical research.
The current staffing of theorists at a number of such
centers is compared with the total (Ph.D. equivalent)
scientific staffs in Table 4.1.
OCR for page 276
276
TABLE 4.1 Staff Theorists at Nationally Prominent Centers
Theorists
Center
Permanent
Permanent Scientific
Staff Postdocs Staff
Kitt Peak National 1 2 35
Observatory
Cerro Tololo Inter- 0 0 10
American
Observatory
National Astronomy 0 0 11
and Ionospheric (astronomers)
Center
National Radio 1.5 3 30
Astronomy
Observatory
Smithsonian 5.3 - 40
Astrophysical
Observatory
NASA-Goddard Space 4 6 40
Flight Center
NASA-Goddard 3 5 5
Institute for
Space Studies
NASA Ames Research 6 3 14
Center
The total NSF support of theoretical astrophysics,
including the staff theorists at the National Astronomy
Centers, represents approximately 5 percent of the NSF
annual astronomy budget (approximately $57 million in
fiscal year 1978). The NASA support of theoretical
astrophysics including staff theorists at astronomical
research centers represents approximately 1.2 percent of
the NASA budget for astrophysical science (about $230
million in fiscal year 1979).
Solar and solar-system research have been excluded
from the above figures because these areas are funded in
different ways. Most of the NSF funding of solar theory
OCR for page 277
277
is through the atmospheric sciences section. The largest
NSF program for solar theory is at the High Altitude
Observatory (MAO) of the National Center for Atmospheric
Research, which has 12 solar theorists and a total scien-
tific staff of 20.
NASA has a program for the support of theoretical
studies in solar terrestrial physics, currently funded at
a level of approximately $1.4 million/year (fiscal year
1979). As a result of the recommendations of the Space
Plasma Physics report of the Space Science Board (National
Academy of Sciences, Washington, D.C., 1978), this theo-
retical effort has been augmented by a new program funded
at a level of $2.2 million/year (fiscal year 1980).
The Department of Energy (DOE) makes a significant con-
tribution to theoretical astrophysics by supporting Part-
time research in astrophysics by staff members at the Los
Alamos and Livermore National Laboratories. These labora-
tories also support some theorists at universities through
visiting scientists programs, especially in those areas
involving the special expertise of these laboratories,
such as numerical hydrodynamics, stellar structure, super-
nova explosions, nucleosynthesis, and gravitational
collapse.
The National Bureau of Standards (NBS) supports re-
search in theoretical astrophysics at the Joint Institute
for Laboratory Astrophysics (JILA) by three staff scien-
tists and typically two or three visiting scientists.
This support provides a valuable link between the NBS
programs in atomic and molecular physics and astrophysics,
particularly in the area of radiative transfer theory.
The support of theory by NSF at the National Astronomy
Centers contrasts sharply with that in other sciences.
For example, in high-energy physics the major DOE labs
have theory groups that are substantial fractions of the
total scientific staffs: 15/103 at Brookhaven; 16/146 at
Fermilab; and 26/120 at the Stanford Linear Accelerator
Center (SLAC). These theory groups, particularly the one
at SLAC, are comparable in quality with the best univer-
sity departments and strengthen the interaction between
experiment and theory and between the laboratories and
university departments. This has occurred, for example,
at the Smithsonian Astrophysical Observatory, where
theorists interact effectively with the Harvard College
Ohservatorv and with the observational programs in infra-
red, ultraviolet, optical, and x-ray astronomy. We sug-
gest (see, for example, Recommendations 1 and 2 below)
_ ~ ~ ~ ~ . . ~
OCR for page 278
278
that strong theory groups at the National Astronomy
Centers should play a similar role.
In our opinion, the support of theoretical astrophysics
research at the universities has declined to a dangerously
low level. The funding of theory at universities with
substantial and excellent programs in astrophysics was
once adequate to support lively groups of students, post-
doctoral fellows, and visiting scientists. These programs
are now underfunded, and the resulting lack of flexibility
threatens their vigor. Of even greater concern to this
panel are the examples we have seen of excellent theorists
who have been unable to obtain funding or who have faced
great delays in obtaining funding.
A study of the 1979 issues of the Astrophysical Journal
reveals the following statistics on the publication of
theoretical papers: 533 different authors published one
or more papers, 124 published two or more, and 48 pub-
lished three or more papers. From these statistics,
keeping in mind that many of the 533 authors publish less
frequently than annually, we infer that some 100-200
people are active theorists. An additional 30 permanent
theoretical positions would therefore have a significant
impact on theoretical research.
As discussed in the report by the Panel on Organiza-
tion, Education, and Personnel (see Chapter 6), the rate
at which universities appoint astronomers to faculty
positions is expected to remain very low throughout the
1980's. We note also that the production of new Ph.D.'s
in theoretical astrophysics has dropped precipitously in
the past two years, and we expect this rate to decline
further and remain low. But, as we have argued, the
explosion of astronomical data creates an increasing need
for theoretical research during the 1980's.
There is now a reservoir of well-trained and highly
qualified theorists who are in a "holding pattern" of
temporary postdoctoral research positions. While one or
two years of postdoctoral study has been a desirable
tradition for young theorists, the shortage of permanent
positions has forced many theorists into their second or
even third postdoctoral appointment. A decade ago these
people would have had no difficulty in finding a faculty
position at a research-oriented university department,
but now such positions are lacking. The existence of
this holding pattern signals the prospect of a lengthy
period of disruptive relocations and career uncertainty;
it discourages excellent young scientists from pursuing a
OCR for page 279
279
career in theoretical astrophysics. Yet a continuing
production of theorists is required for the future bal-
ance of the science. Therefore, we consider it imPera-
tive that some 30 new permanent positions for theoretical
astrophysicists be created within the next decade.
It is sometimes suggested that since the best young
theorists are still highly sought after, there is not a
serious shortage of permanent positions for theorists.
We believe that such suggestions are based on unwarranted
confidence in the ability to predict future performance.
Furthermore, we have noted several examples of outstand-
ing young theorists with the potential to do excellent
research who have not been able to find positions in
research-oriented departments and have left the field
entirely.
E. Recommendations for Theoretical Astrophysics
We believe that the astronomical community has an out-
standing opportunity to remedy the deficiencies of the
current program for theoretical astrophysics. At the
time when unprecedented demands are confronting the
science, we have a reservoir of well-trained and highly
motivated young theorists. Likewise, the increasing role
of computers in astrophysics coincides with a revolution
in computer technology. Three principles have guided our
suggested program for theory embodied in the recommenda-
tions here: (1) An appropriate mix of theorists and
observers should be involved in every astronomical enter-
prise; an imbalance toward either observation or theory
in institutions for astrophysical research is unhealthy.
(2) We must create approximately 30 new permanent posi-
tions for theorists to meet the challenge posed by the
impending explosion of astronomical data. (3) We must
establish a funding pattern adequate to ensure that the
theoretical community can function effectively, by inter-
acting with other theorists and by exploiting the power
of modern computers.
RECOMMENDATION II .1: The National Aeronautics and Space
Administration should establish a strong, broad program
of investment in theoretical astrophysics research. This
program should relate to present and future space astron-
omy missions and should include three components: (a)
the support of theoretical astrophysics through contracts
OCR for page 280
280
and grants, (b) a substantial increase in the number of
staff theorists at the NASA centers; and (c) increased
involvement of theorists in astronomical mission programs.
m e NASA missions of the 1980's will be fully effec-
tive only if they are developed on a firm scientific foun-
dation involving a close interaction between observers and
theorists. One of our primary recommendations is that the
NASA practice of "exploration first, then extensive obser-
vation, then theoretical analysis" be replaced by a more
sophisticated and responsive recognition of the simultane-
ous and complicated intellectual processes that actually
occur in the interplay between observation and theory.
New observational initiatives must be based on a
healthy theoretical body of knowledge. It appears to us
that in the 1970's this obvious point was neglected. NASA
has a particular responsibility to support the growth of
theory, for it has gained much from the existing knowl-
edge. For example, the extraordinary fruitfulness of
x-ray astronomy is in part due to the large applicable
range of the previously developed plasma physics, the
physics of matter at high temperatures, and General
Relativity, which could be brought to bear on understand-
ing the observational discoveries of the field. mese
areas of theory were developed originally for other
purposes. NASA has made no comparable investment in the
development of these basic theoretical understandings,
which will suggest new directions in space astronomy or
be the analytic tools for understanding the results of
the observational programs to which the agency is already
committed.
As a minimum that is not only consistent with NASA's
mission agency status but also seems required by that
status is the investment by NASA in basic astrophysical
theory at a level compatible with the amount of theory
tnat in effect it consumes. Otherwise we will see new
., . . _ _ . . .
mission ideas that are less innovative, less productive,
and less valuable scientifically. Space-based astronomy,
ground-based observations, and theoretical astrophysics
can be complementary. NASA should make its own investment
in the broad development of astrophysical theory and in
the 1980's, should develop a vigorous program of theo-
retical support in order to provide intellectual and
conceptual leadership for the 1990's and beyond.
We applaud the recent decision by NASA to increase
substantially the support of theoretical studies in solar-
system plasma physics. We believe that this new program
is an excellent response to the concerns raised in the
OCR for page 281
281
Space Science Board report, Space Plasma Physics, and
will greatly enhance the effectiveness of the NASA pro-
gram of solar-system exploration. We suggest that a
similar program to support theoretical astrophysics
research would greatly strengthen the NASA program in
space astronomy, and we make the following specific
recommendations:
(a) A NASA grant/contract program should be estab-
lished specifically to support the investment in theoreti
cal astrophysics that is needed now, if there is to be an
innovative space observational program in the 1990's and
beyond. This theory program should be separated from
current specific mission objectives. All fields of theo-
retical astrophysics should be represented since many of
the theoretical advances most important to NASA's objec-
tives cannot be foretold. The program should have a
separate program director (cf. Recommendation 4), and
proposals should be judged on the basis of peer review.
We suggest an initial funding level of $4 million/year in
fiscal year 1980 dollars.
(b) m e NASA centers for astronomical research,
and in particular the Space Telescope Science Institute,
should acquire and maintain strong theoretical staffs
(see Recommendation 2). In-house theoretical expertise,
if of sufficient depth, breadth and quality, can play an
important role in helping to create the ideas of future
missions. Without being tied to specific missions, the
NASA theorist can be a bridge between theory and NASA
program objectives and provide effective communications
between NASA and the external community of theoretical
astrophysicists.
(c) Theorists should be an integral part of astro-
nomical mission programs. The purpose of a mission team
is to make possible the application of diverse techniques
and scientific backgrounds, in order to achieve increased
understanding. We consider theoretical study to be an
additional and distinct means of achieving that under-
standing, and it should be thus represented as a matter
of course. Theory often suggests the way to more mean-
ingful measurements, and theorists should be involved in
mission planning and definition as well as data analysis
and interpretation of results.
RECOMMENDATION II.2: The National Astronomy Centers
(e.~., National Radio Astronomy Observatory, National
Astronomy and Ionosphere Center, Kitt Peak National
-
OCR for page 282
282
Observatory) should acquire and maintain a theoretical
scientific staff adequate to meet the demands imposed by
their observational programs.
As described earlier, the National Astronomy Centers
are seriously undermanned with theorists. These facil-
ities maintain large staffs of observers, and we believe
it vital for the future health of astronomy that an equiv-
alent theoretical component be established. Specifically,
we advocate that the ratio of theorists to observers
should be on the order of 1:5, roughly comparable with
the ratio found in the larger university departments and
high-energy physics laboratories.
To be fully effective scientifically, the observational
programs of the National Centers need the support of a
strong theoretical research activity. Because the obser-
vational programs are extremely varied, the theoretical
support must have a breadth that cannot be provided by a
small group, however competent. Effective theory, espe-
cially of the interpretative or phenomenological kind,
requires a minimum critical number of active theorists
working closely in association with each other and with
observers. Postdoctoral positions for theorists are a
useful mechanism for introducing new ideas, but the occu-
pants operate with high efficiency only with the presence
of a permanent staff. Data analysis and software develop-
ment should not be the primary responsibilities of the
theory group. However, theorists can and should partici-
pate in the planning of future observational programs and
instruments.
,
The policy we recommend must be strongly supported by
the Center Directors and the funding agencies; otherwise
the positions will be subjected too readily to immediate
economic pressures and sacrificed to short-term needs.
We are opposed to the creation of a National Center
for Theoretical Astrophysics, and we do not recommend
that we follow the example of the physics community. A
greater return for the funds would, in our view, be
obtained by creating positions for theoretical astro-
physicists at the National Centers, where they can di-
rectly influence the observational programs and provide a
mechanism for improved communication with theorists at
universities (cf. Recommendation 5).
Theorists have often grown into talented observers.
The trend is not to be discouraged, but such losses to
the theoretical staff should be balanced by new appoint-
ments.
OCR for page 283
283
If our recommendation is followed, we believe that the
large portion of the nation's resources in observational
astronomy that is employed at the National Centers will
be applied with greatly enhanced effectiveness.
We emphasize that this recommendation should not be
implemented at the expense of theoretical research at the
· · .
universities.
RECOMMENDATION I I .3: A concerted effort should be made
to provide advanced computer technology to theoretical
astrophysicists.
As discussed earlier, the increasing role of computers
in astrophysical theory predicted by the Greenstein report
has now become a reality. However, access by theorists
to computing power remains uneven and lags the develop-
ment of the technology. Three recent developments create
an outstanding opportunity for astrophysics.
First, there has been an intellectual explosion in the
interest among theorists in two- and three-dimensional
problems in computational astrophysics. This is fueled
both by intrinsically theoretical considerations and by
the increasing spatial and spectral resolution of the
observations. Examples of such problems are the dynamics
of fluids, plasmas, or stellar systems in two and three
space dimensions or of photons, neutrinos, cosmic rays,
or stars in energy space and one or two space dimensions.
The advance to higher dimension permits the investigation
of qualitatively different phenomena that cannot be quan-
titatively studied otherwise and are fundamental to our
understanding of astrophysical systems. (For example,
convection does not appear in one-dimensional hydro-
dynamics.)
Second, there has been a technological explosion in
computer development. The decrease in cost and increase
in power of computers is projected to continue unabated
through the 1980's. Computational capability at a level
that has existed only at a few major centers for computa-
tion can now be brought to typical astrophysical research
facilities. For astrophysical theory, the most spectac-
ular improvement in cost-effectiveness has been not in
supercomputers but rather in more modest, medium-scale
machines with large virtual memories (especially when
considered in conjunction with array processors).
Third, there has been an explosion in the number of
theorists interested in developing innovative uses of the
new technology for theoretical problems. For the theorist
the development of software for the new computers is
OCR for page 284
284
analogous to instrument development for the observer;
funding of such development is necessary to explore the
possibilities presented by the new and rapidly changing
technology. It is vital for the health of theoretical
astrophysics that the opportunity to capitalize on these
developments not be lost or delayed.
We recommend a balanced and flexible program, including
the installation of dedicated machines at existing centers
for theoretical work, access to the most powerful comput-
ers at national centers and DOE laboratories (cf. Recom-
mendation 6), and continued use of university computing
facilities as appropriate. We expect that such a program
will involve a much larger fraction of the theoretical
community in the formulation, analysis, and criticism of
numerical theory. We need reliable theory to interpret
the old and to guide the new observations, and a deeper
interaction between numerical and analytical theorists is
a vital step toward that goal. Visitor programs are
important for scientists who lack good local facilities
(cf. Recommendation 5).
RECOMMENDATION II.4: The National Science Foundation
should establish a separate program director with
responsibility for theoretical astrophysics.
Under the present arrangement, which divides astronomy
artificially into the subdisciplines of "Stars and Stellar
Evolution" and "Galactic and Extragalactic Astronomy,"
theory suffers. Good theory recognizes no arbitrary
boundaries, and theoretical principles and techniques
applicable in one area are valuable in the other; indeed,
the research of many theorists can be placed equally in
each category. m e recommendation for a new administra-
tive arrangement, similar to that of the Physics Division,
would increase the effectiveness of NSF support of astron-
omy by providing a mechanism for the development of a
balanced long-term theoretical program. It would also
provide an identifiable point of contact for theorists,
which would be of particular value for young theorists
seeking support for the first time.
RECOMMENDATION II.5: A network for close communication
among theorists should be supported through summer
institutes, workshops, and scientific visits.
Theory plays a centripetal role in astronomy. The
maintenance of the network recommended here provides an
essential framework for the effective functioning of the
theoretical community and requires a diverse and flexible
OCR for page 285
285
support pattern. Developments in theoretical astrophysics
tend to be both rapid and complex, so that face-to-face
discussions with colleagues are the only fully adequate
way of keeping abreast of many areas.
Summer institutes, such as those at Aspen and Santa
Cruz, have been extremely productive in inspiring both
ideas and research collaborations. Programs to support
visitors, at both universities and National Centers, can
be very valuable. Extended visits are often most produc-
tive, but short visits are usually easier to arrange, and
both should be judiciously supported. We believe that
well-planned visitors' programs at a number of institu-
tions can achieve some of the goals of a national theory
institute in a more effective and economical manner.
Likewise, foreign-exchange programs and international
workshops have been extremely valuable. The support of
travel by theorists is a vital component of the mainte-
nance of a vigorous communications network. Unfortu-
nately, this fact has not been fully recognized by the
funding agencies, because travel for theoretical research
cannot be justified in such concrete and immediate terms
as travel for observing.
Support for the temporary relief from teaching duties
should be available to capable theorists; this should be
viewed as a routine device to initiate important projects
and to increase scientific range and productivity.
Highly talented theorists and promising theoretical
programs should be supported wherever they are. The late
1970's and early 1980's have seen, and will continue to
see, a dispersal of young astrophysicists at the highest
level of ability among institutions that cannot maintain
large research groups in this area. The problems faced
by theorists at these institutions are particularly acute.
The programs we suggest here offer a particularly cost-
effective way to maintain high enthusiasm and to increase
the scientific productivity of the theoretical community
as a whole and should be supported as they serve that
purpose.
RECOMMENDATION II.6:
The Department of Energy labora-
tories should maintain a continued involvement with
theoretical astrophysics.
As noted earlier, the Livermore and Los Alamos National
Laboratories make a significant and valuable contribution
to theoretical astrophysics research. We urge continued
and expanded support of this research by the Department
of Energy and other federal agencies because of its value
Representative terms from entire chapter:
observational programs
