Beatrice Tinsley: A Tribute

by Robert C. Kennicutt, Jr.

Robert Kennicutt is Professor/Astronomer at the University of Arizona's Steward Observatory, where he
works on extragalactic astronomy and galactic evolution. He is also Editor-in-Chief of The Astrophysical Journal.

January 2005

This article is based on the opening talk given at the conference Stellar Populations 2003, held in Garching, Germany on October 6–10, 2003. The conference was dedicated in memory of Beatrice M. Tinsley.

It has become customary in our profession, when a distinguished scientist reaches the age of 60 or
beyond, to organize a conference in his or her honor, a Festschrift. If Beatrice Tinsley were still with
us today there is little doubt that we would be holding this conference on Stellar Populations in her honor.
Unfortunately 22 years have passed since Tinsley’s death at age 40, so she was deprived of her Festschrift.
But this has not deterred the organizers of this conference from dedicating the meeting in her memory
just the same. This is not the first such conference dedicated in her memory. The very first STScI
Symposium in 1985, also entitled Stellar Populations, was dedicated to Beatrice, and that meeting opened
with a similar dedicatory talk by Jim Gunn.

For the many of you who never met Beatrice Tinsley or worked on the subject when she was
active, it may come as a surprise that her colleagues would still be honoring her memory so
many years after her death. My task in this talk is to explain why. I approach the task with some
reluctance, because unlike Jim Gunn and her other close collaborators, I only met Tinsley briefly at the
end of her career (and at the beginning of my own), so I cannot speak from firsthand observation. This is
important because much of the greatness in this complex person came from the way in which she interacted
with other scientists, young astronomers in particular. So in order to remain on solid ground I will focus most of my talk on her many fundamental contributions to the subjects of stellar populations and galaxy
evolution, and the aspects of her science that were so special. Whenever appropriate I have added a few
remarks about her life and the personal qualities behind her success, based on published accounts
(some of which are listed at the end of this article) and from conversations with many of her colleagues and
friends. Hers is a remarkable story of scientific genius, personal courage and perseverance, and generosity of spirit, and there are lessons in the story for all of us.

Early Life and Graduate School: 1941–1967

Beatrice Muriel Hill was born in 1941 in Chester, England. Her family moved to New
Zealand five years later, and she remained there through college. Today she is embraced as a
national hero in her adopted homeland (see http://www.nzedge.com/index.html). Her intellectual
brilliance became apparent at an early age, and by age 14 she had decided to pursue a path in
astrophysics. She graduated from high school at age 16 and entered Canterbury University, where she
earned a First in Physics (BSc), followed by an MSc degree in 1963. While in school she married a fellow
space physicist, Brian A. Tinsley, and 1963 the couple moved to Dallas, where Brian had been offered a
long-term position at what is now the University of Texas at Dallas. For the next 13 years Beatrice filled
the all-too-familiar role of the trailing partner, and in the absence of a permanent job supported herself
with an assortment of part-time teaching positions, visiting appointments, and research fellowships.

Since UT Dallas did not offer a doctoral program in astronomy at the time, Tinsley enrolled
in the newly created Ph.D. program at UT Austin, and commuted the 200 miles weekly to complete her
degree. Her graduate career at Austin is a department legend. She completed her degree in record time
(1964–1967), working largely on her own, and the thesis that emerged became a landmark work in its
field. When The Astrophysical Journal published a collection of 53 seminal papers from the 20th century
in its 1999 Centennial Issue, Tinsley’s thesis paper Evolution of the Stars and Gas in Galaxies was one
of them (Tinsley 1968, ApJ, 151, 547; also ApJ, 525C, 1146*). In her thesis Tinsley developed,
virtually from scratch, the theoretical apparatus for constructing evolutionary synthesis models of the
colors, gas contents, and chemical abundances of galaxies. She then applied her models to two
fundamental problems, the evolutionary nature of the Hubble sequence, and the change in the observed
magnitudes and colors of galaxies with cosmological look back time. In this one paper she helped to
establish the modern evolutionary picture of the Hubble sequence, and demonstrate that the effects of galaxy evolution were readily observable to even modest redshifts, and thus needed to be accounted
for in the prevailing cosmological tests of the time.

* For a more detailed commentary on this paper see Centennial Issue, Kennicutt 1999, ApJ, 525C, 1165.

From today’s perspective, when anyone can access web-based model programs and compute a full
grid of evolutionary models in a few mouseclicks, it is difficult to overstate the groundbreaking and
forward-looking character of this work. For the modeling she had to collect evolutionary tracks from
dozens of papers, and use color-magnitude diagrams of star clusters to reverse engineer isochrones and
tracks for for masses and evolutionary phases where theoretical models were not yet available (including
for red giant stars, which dominate the light in many galaxies). Then the same for stellar atmosphere models, synthetic colors, and nucleosynthetic yields, and finally to make the whole population synthesis, star formation, and chemical evolution machinery run efficiently on 1960s generation
computers. The thesis was no less impressive in its bold scientific vision, given the state of knowledge
at the time. In 1964, when she embarked on her graduate work, the Crab pulsar had yet
to be discovered, and the seminal work by Fowler and others on stellar nucleosynthesis was only
a few years old. Photographic observations of “high-redshift” galaxies barely extended to
redshifts of a few tenths, and the nature of quasars had only been established a year earlier.
The discovery of the cosmic microwave background was still two years away, and the Big
Bang paradigm itself was not yet firmly rooted. Despite this shaky ground Tinsley forged ahead with
a daring set of calculations that paved the way for the modern subject of galactic evolution theory.

In order to test the efficacy of the models Tinsley first computed the expected broadband colors of
present-day galaxies and compared them to the observed progression of colors along the Hubble
sequence. She discovered that she could roughly account for the observed sequences of colors, gas
fractions, and stellar mass/light ratios of galaxies with a set of models with a fixed maximum stellar age,
composition, and IMF, with only one parameter— the age distribution of the stars—varying along
the Hubble sequence. This remains the standard interpretation today, and despite the computational
shortcuts those 1968 models still provide a reasonable fit to contemporary observations, even
out to redshifts of 1 and beyond.

But the main objective was to compute the evolution in galaxies properties with cosmological
lookback time. Tinsley used her models to calculate how the luminosities, colors, gas contents, and chemical abundances of galaxies evolved with cosmic time, and then applied these in turn to quantify how
evolutionary brightening (what we today call“passive evolution”) would affect the use of elliptical
galaxies as standard candles for constraining the geometry and deceleration history of the universe.
Today these tests are performed using supernovae, but at the time it was believed that red galaxies were
stable enough in their photometric properties to be applied as cosmological standard candles—a
program tracing back to Edwin Hubble himself. Tinley’s results showed that the evolutionary effects
were much larger than had been estimated earlier— by factors of several—and that
uncertainties in the evolutionary inputs overwhelmed any effects expected from different cosmic
expansion histories. Galaxy evolution would need to be understood much better before
galaxies could be used to measure the geometry and expansion history of the universe.

Thus this boldly conceived thesis led to a bold conclusion, leaving open whether observations
of distant galaxies really could reveal the history of cosmic expansion and determine whether
we lived in an open or closed universe. The most enduring result of the thesis was its
clear demonstration that galaxy evolution was an eminently observable phenomenon,
even to the modest redshifts that were accessible 35 years ago, and worthy of detailed study in its own right. Within a decade this new subject would grow into one of the largest subfields in extragalactic astronomy.

Dallas: 1964–1974

The years in Dallas that followed her thesis brought yet more scientific accomplishment, but
frequently were tempered by professional and personal isolation and frustration. Reaction in the
extragalactic community to her thesis results were mixed, as might be expected for such a revolutionary
work. Some colleagues recognized the brilliance in the work immediately, and soon initiated long-distance
collaborations that would help to sustain her through the remaining years in Dallas. Others expressed
skepticism or awaited confirmation of the results from other, more senior workers. As other groups
caught up most of her main results were confirmed, and with it her international reputation grew.

Over the next seven years Tinsley published approximately 20 papers, which taken as a whole
laid down much of the foundation for the modern subject of galaxy evolution. These included
papers that extended and solidified the results of her thesis, along with new investigations of the stellar
populations in the solar neighborhood, the IMF, tests of stellar evolution models, nucleosynthetic constraints on galaxy evolution, supernova rates, the cosmic background radiation, the cosmic mass density, and even the cosmological constant! Some of these papers were written alone, but an increasing number were written with long-distance collaborators, including a few names you may recognize: Jean
Audouze, Peter Biermann, Al Cameron, Richard Gott, Jim Gunn, Jerry Ostriker, William Rose, and
David Schramm. I don’t know whether this extraordinary cohort testifies to the insight of her
collaborators in recognizing an exceptional young talent, or instead to Tinsley’s impeccable judgement in
selecting them as collaborators! Probably a combination of both. The breadth of subjects
represented by these individuals testifies to Tinsley’s own broad interests, and her remarkable
ability to synthesize the requisite inputs from these diverse fields to the common problem
of galaxy evolution was widely admired by her contemporaries.

The pressures of sustaining an active research program while supporting herself
on soft money and raising two young adopted children were exacerbated by repeated failures to find
a permanent job in Dallas. The disconnect between her growing international reputation—which by the
mid-1970s included visiting appointments at Caltech, Maryland, and UT Austin, and permanent job offers
elsewhere—and the lack of tangible recognition at home became an immense source of frustration, as
documented in letters to her father at that time. The breaking point—and turning point—in her career
came in 1974, when she filed for divorce and left Dallas to establish a career elsewhere, first at Lick on
a visiting position and in 1975 to a tenure-track faculty position at Yale, where she worked for the
remainder of her life.

Yale: 1975–1981

At Yale Tinsley’s intellectual productivity and creativity blossomed. She published some 60 papers
over these seven years, initiating major long-term studies of galactic and chemical evolution, and turning
her attention increasingly to cosmology. Soon the balance of her papers shifted away from long distance
collaborations with fellow pundits, and increasingly toward papers written with students and a few long-term collaborations, most notably with Richard Larson, another young faculty member at Yale.

The range of problems that Tinsley addressed in these papers covered the full sweep of modern galactic
evolution theory. They included a series of fundamental papers on chemical evolution theory,
including a widely influential review paper with Jean Audouze. With Larson she refined her evolutionary
synthesis models of galaxies, made some of the first quantitative estimates of star formation rates in
galaxies, and applied them to the problems of interaction-triggered star formation, the effects of
cluster environment on galaxy evolution, and the cosmic star formation rate and history. Her famous
1978 paper with Larson on star formation in interacting and peculiar galaxies (Larson & Tinsley
1978, ApJ, 219, 46) quantified the properties of what are known today as starburst galaxies, and
demonstrated the importance of galaxy interactions and mergers as triggering agents for these bursts. She
continued to explore the prospects for testing cosmological models with observations of distant galaxies,
and she was among the few established scientists at the time to champion the possible existence and
importance of a cosmological constant.

One of the highlights of her career at Yale, and one of her most lasting contributions to our subject, was her organization with Larson of the 1976 Yale conference The Evolution of Galaxies and Stellar
Populations. She drew on her breadth of knowledge to design a conference that soon became regarded as a watershed in the subject. Galaxy evolution was on the verge of a paradigm shift as the first observational and theoretical evidences of hierarchical galaxy assembly and evolution were being manifested, and all of them were represented here: the early results by Searle and Zinn on the assembly of the Galactic halo; a review by Spinrad of observations of high-redshift galaxies and the newly discovered Butcher-Oemler effect; a classic paper by Alar Toomre on the galactic merger sequence; a review by Martin Rees laying down the cosmological foundation for the new hierarchical picture; papers by Strom, Ostriker, and van den Bergh on environmental effects on galaxy evolution and classification; a review by Faber on the interpretation of integrated spectra and abundances in elliptical galaxies; and of course the work by Larson and Tinsley themselves on star formation rates and interactiontriggered starbursts. Dog-eared copies of the blue-covered proceedings from this meeting soon populated the bookshelves of most graduate students and postdocs in the field, and the workshop itself became the standard by which all subsequent meetings in the field were judged.

When one reviews Tinsley’s bibliography a few obvious things stand out, for example the amazing
breadth of her published work and the intellectual creativity that is evidenced in her choice of research
topics. Upon closer examination several deeper patterns emerge. One was her resilience and
adaptability to new ideas. As the first glimmers of the hierarchical paradigm for galaxy formation and
evolution emerged during this period, Tinsley and Larson were among the first to calculate photometric
and chemical evolution models for merger-dominated systems. Instead of clinging to the old-school paradigm that had served as the foundation for most of her life work, she quickly embraced the radical new model, and her advocacy led others to pay serious attention to the emerging new paradigm.

Most impressive of all to me is the extraordinary scope and vision of her work. If you delve deeply
into her published work you will find a handful of long-forgotten gems of ideas that were decades
ahead of their time. Let me share three of my favorite examples. The most cited of the three, with a total of
22 ADS citations in 26 years, is a paper written with Rasheed Sunyaev and David Meier, with the
provocative title Observable properties of primeval giant elliptical galaxies or ten million Orions at high
redshift (Sunyaev, Tinsley, & Meier 1978, Comments in Astrophysics, 7, 183). In this paper the authors
calculate the multi-wavelength spectral energy distribution of a young starburst galaxy, and consider
how such objects might be detected at high redshift. They derive a synthetic restframe ultraviolet spectrum
for the galaxy (using UV spectra of stars recently obtained with the Copernicus Observatory!), and
correctly surmise that the best strategy for identifying very high-reshift galaxies (z > 2) would be by detection of the redshifted UV stellar spectra using large groundbased telescopes. They go on to point out
that the most massive starbursts might be heavily obscurred by dust, in which case the detection of the
redshifted far-infared continuum (which they also model) would provide another means of detecting
these objects.

My second example, with a total of 20 ADS citations in 24 years, was written with a Yale undergraduate
student (Laura Danly), and is On the Density of Star Formation in the Universe (Tinsley &
Danly 1980, ApJ, 242, 435). This paper holds special interest for me because it contained one of the first
prescriptions for measuring integrated star formation rates (SFRs) in galaxies. But the paper goes much farther; the authors apply this method to measure the local cosmic SFR density, and to constrain its evolution with cosmological lookback time. Although the paper does not contain a figure with the now-famous Madau-Lilly plot, all of the supporting elements are there, including a plot of the evolution with redshift of the gas mass in galaxies.

Finally my personal favorite, with a total of four ADS citations in 32 years, is one of those
single-author paper written during the Dallas years, Photoionization by Massive Stars in Protogalaxies
(Tinsley 1973, Ap Letters, 14, 15). In it she calculates the conditions under which the first generation of
massive stars formed in the early universe might reionize the intergalactic medium. Although it was a
simple calculation compared to those contained in the hundreds of papers on cosmological reionization
written over the past five years, it demonstrates the reach of her vision 30 years ago. One can only wonder
what future cutting-edge science topics may still lie hidden in those papers.

Final Years and Legacy

The year 1978 brought another one of those bittersweet turning points in Tinsley’s life. In that
year she was promoted to the rank of Full Professor at Yale, with the security of a tenured academic position—no small matter for a single mother in that era. At the same time she learned that she had contracted a virulent strain of melanoma, with little prospect of survival. After coming to terms with the initial shock of this revelation she threw herself into fighting the disease and making the most of whatever time remained. Over the next three years she published some of her very best papers, including her magnum opus, the review Evolution of the Stars and Gas in Galaxies (Tinsley 1980, Fund Cos Phys, 5, 287). This 100-page article is a veritable textbook on galactic and chemical evolution theory, and a bible for those of us who followed in her footsteps. It stands far-and-above as her most cited paper, and it continues to be read and cited heavily to this day. Other papers addressed the role that dark matter might play in explaining some of the evolutionary trends along the Hubble sequence, yet more evidence of that
resilience and vision that was alluded to earlier. Her last paper, on analytical modeling of chemical
evolution, was submitted for publication a few days before she succumbed to the cancer in March of 1981.

During her short career Beatrice Tinsley had a number of honors bestowed upon her, including the
University of Canterbury’s Hayden Prize for Physics when she graduated in 1962, and the AAUW/AAS
Annie Jump Cannon Award in 1974. It was only after her death that our profession fully appreciated
what it had lost, and many more honors have been bestowed upon her posthumously. In 1984 the
University of Texas at Austin established an endowed visiting professorship in her name, and I am proud to
be among those who have been honored with that appointment. In 1986 the AAS established its Beatrice
M. Tinsley Prize for research of an especially creative or innovative character.

Since I began writing and speaking about Beatrice Tinsley five years ago I am frequently asked
the same questions again and again. How could she (or any scientist) accomplish so much in such a short
lifetime? What was her secret? And then the question that opened this talk: Why do scientists of my
generation—even people like me who did not interact closely with her— hold such a strong emotional attachment to this long-departed scientist, now more than 23 years after her death?

At the risk of injecting too much of my own personal interpretation into another person’s
motivations, my own sense is that some of the same personal characteristics can provide insights into all
of these questions, and they can provide useful lessons for all of us. Why was she so successful? There
are some obvious factors: exceptional intellectual brilliance and creativity combined with immense
drive and tenacity for sure, personal characteristics that were fired in that crucible in Dallas. But these
obvious factors provide only part of the answer. The rest becomes clear whenever you speak about Tinsley
with her colleagues and friends. They all cite two personal characteristics. One was her immense
curiosity and broad scientific interests, which spanned any aspect of stellar, interstellar, extragalactic,
or cosmological physics that might be relevant for understanding galactic evolution (in other words,
just about everything!). As mentioned earlier, galaxy evolution really is not a free-standing subject on its
own, but rather a synthesis of everything we know about subjects ranging from star formation and
evolution to the physics of the ISM to the intricacies of stellar dynamics, hydrodynamics, nuclear astrophysics, and cosmology. Tinsley was remarkable both for her broad grounding in all of these subjects, as well as her ability to synthesize this immense swath of science in order to construct a new evolution
model or to crack a specific problem in galaxy formation or evolution. And although she was
trained as a theorist and devoted virtually all of her career to theory, she maintained an intense interest in
and engagement with astronomical observations. Whether you were a theorist or an observer she was
interested in your work, and scores of young observers of my generation gained inspiration from
the attention that this eminent theorist bestowed upon their work. As pointed out in one of her obituaries in
1982, the number of her published papers were rivaled only by the number of papers by others that
carried an acknowledgement to her for insightful comments or contributions. And I am convinced that
this voracious appetite for new work in all of these fields was one of the secrets to her success. By keeping
on top of the literature across such a broad expanse of research topics she was always among the first to
identify new opportunities and research directions.

The other personal characteristic that is cited by her contemporaries, above all, was her deep interest
for the welfare of the young scientists in her field, and her openness and generosity in her day-to-day
interactions with them. That may have been yet another secret to her success; what better way to stay
on top of a growing field than spend time with the young scientists who had the time to take on the really
difficult problems, and who were unafraid to challenge the old ideas? But this engagement with
young scientists was mainly borne of generosity of spirit, and in that respect it represented an interesting
study in contrasts. Although most published accounts of her life (mainly published shortly after her death)
describe her personality and character in wholly uplifting terms, as befitting the times, this tends to
render a one-dimensional impression of a much more complex and three-dimensional person. In
addition to her other qualities Tinsley was bold, ambitious, direct, critical, and exacting in her
expectations of herself and others. She often could be brash and sharp-edged in her professional interactions, and she certainly did not suffer fools well, especially old fools who should have known better.
But these tendencies were tempered (most of the time) when she interacted with her younger and
more vulnerable junior colleagues.

Soon after arriving at Yale she took charge of the graduate program, and served as an advocate for the
welfare of the students generally. Outside the department, stories abound of young scientists
receiving a cheerful note or preprint card in the mail after the publication of one of their first papers, often
with an invitation to visit New Haven. As a result the department became a magnet for bright young
scientists in this emerging field of galaxy formation and evolution. These correspondences and interactions
continued through the last months of her life, when she became bedridden and partially paralyzed. Even
then the scientific projects, collaborations, and personal visits continued, and when she lost use of
her writing hand she taught herself to write lefthanded, so the correspondence could continue up
up to her last few days.

Therein lies the answer to why we memorialize this remarkable individual more than two decades
after her death. In a profession that to this day confronts a young scientist with an endless gauntlet
of opportunities for disappointment and negative feedback, Beatrice Tinsley was able to recognize and
tap the enormous curative power that a little bit of positive feedback and encouragement could have on
the motivation and self-confidence of a young astronomer, especially for a young scientist working
in the 1970s, and, most of all, for a young woman scientist working in the 1970s. That influence has
endured as she continues to serve as a role model for the succeeding generations of women in our profession. Although I would like to believe that the climate for today’s young scientists has improved dramatically since her time, we all could profit by being a little bit like Beatrice and dispensing some of that curative medicine of encouragement ourselves from time to time. That would represent a truly meaningful
tribute to her memory.

References
Tinsley, B.M. 1968, APJ, 151, 547
Tinsley, B.M. 1980, Fund Comsic Phys, 5, 287

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