A SHORT BIOGRAPHY OF DR. SHIV S. KUMAR
(ssk @ galileoinstitute.org)
Dr. Shiv S. Kumar was born on March 15, 1939 in Bannu, India (now Pakistan).
After obtaining a BSc (Honours) degree in Mathematics from Lucknow University
(Lucknow, India) in 1957, he joined the University of Michigan (Ann Arbor, Michigan) as
a graduate student/research assistant in the Department of Astronomy. He obtained a PhD
degree in Astronomy from Michigan on February 3, 1962. His PhD dissertation dealt with
the theory of non-grey stellar atmospheres.
In addition to the University of Michigan, he has worked at the following
institutions: Smithsonian Astrophysical Observatory, Cambridge, Massachusetts
(1960-1961); The City College of the City University of New York (1962); Goddard Institute for Space Studies, New York City, New York
(1962-1963); Physical Research Laboratory, Ahmedabad, India (1963-1965); University
of Virginia, Charlottesville, Virginia (1965-1998); Australian National University,
Canberra, Australia (1970-1971). Currently he is president of The Galileo Institute,
Ruckersville, Virginia, and emeritus faculty member at the University of Virginia. The
Galileo Institute, an independent institution for scientific research and education, was
founded by Dr. Kumar in 2000.
Since 1957, Dr. Kumar has worked on the problems of the origin and evolution of
stars of very low mass, the origin of the Solar System, star and planet formation processes,
the theory of stellar atmospheres, the origin and evolution of life in the universe, and other
problems. Most, but not all, of his scientific contributions during the period of 1957-1974
are summarized below:
THE THEORY OF STARS OF VERY LOW MASS (1958-1962)
During the period 1958-1962, Dr. Kumar developed the theory of stars of very low
mass (M < 0.1Msun) which led to several important predictions concerning the structure
and evolution of these objects (1, 2, 3, 4). The theoretical predictions, which have mostly
been confirmed by subsequent theoretical work and/or observational studies, are briefly
discussed below:
1. The first computation of the minimum hydrogen-burning mass limit was completed by
Dr. Kumar in the summer of 1962 when he was working as a NAS-NRC Postdoctoral
Research Associate at the Goddard Institute for Space Studies (New York, New York). The
numerical value of this critical mass varies with chemical composition and his
computations led to the currently accepted values of -0.07 Msun for Population I stars and
-0.09 Msun for Populations II stars. These limits also define the bottom of the hydrogen
burning main sequence in the H-R diagram for the two stellar populations. The hydrogen
burning mass limit has been referred to as the Kumar limit by some scientists (5, 6, 7, 8).
2. The structure and evolution of stars with mass below the H-burning limit was studied by
Dr. Kumar during 1958-1962 while working at the University of Michigan, Ann Arbor,
Michigan (1958-1960), Smithsonian Astrophysical Observatory, Cambridge,
Massachusetts (1960-1961) and NASA’s Goddard Institute for Space Studies, New York,
New York (1962). The main prediction of the theoretical calculations was that the H-rich
stars with mass below the H-burning limit become completely degenerate objects without
ever going through hydrogen-burning thermonuclear reactions. Dr. Kumar referred to
these completely degenerate objects as “black dwarfs” since their luminosity L was
expected to be extremely low (L→0) and their surface temperature T also very low (T→0).
3. It was also predicted by Dr. Kumar that the final radius of the stars with the mass below
the H-burning limit is approximately 0.1Rsun (1, 3).
4. Since the time-scale for the formation of these very low mass completely degenerate
stars (black dwarfs) was calculated to be much less than the age of the Galaxy, Dr. Kumar
predicted the existence of a very large population of “dark” objects (black dwarfs) in the
Galaxy (4).
A more detailed account of Dr. Kumar’s theoretical discovery, during 1958-1962, of the
objects beyond the bottom of the main sequence is available on the Internet (9). Dr. Kumar
has continued his work on the structure and evolution of stars beyond the bottom of the
main sequence since 1962, and has published numerous scientific papers in the field
founded by him. He also organized an international symposium on low-luminosity stars at
the University of Virginia in March 1968. A major topic of discussion at this conference
was the structure and evolution of the stars with mass below the H-burning limit. Many of
the symposium participants referred to these objects as “Kumar objects” or “Kumar stars.”
The currently popular terminology of “brown dwarfs” was introduced in 1975. The
proceedings of the symposium were edited by Dr. Kumar, and they were published as a
book in 1969 (10). Observational searches for stars with mass below the Kumar limit
(currently called brown dwarfs) were started in 1962 and they were finally detected in
1995! (11, 12).
The 50th anniversary of Dr. Kumar’s theoretical discovery of brown dwarfs was celebrated
on October 21, 2012 at an international conference entitled “50 Years of Brown Dwarfs:
from Theoretical Prediction to Astrophysical Studies” held at Ringberg castle, Bavaria,
Germany (October 21-24, 2012). This conference was organized by the Max Planck
Institute for Astronomy in Heidelberg, Germany. Information concerning this historical
celebration event, organized by Dr. Viki Joergens and her colleagues/coworkers at
MPIA-Heidelberg can be found here.(21)
VERY LOW MASS COMPLETELY DEGENERATE STARS AND
DARK MATTER IN THE GALAXY (1962-69)
Dr. Kumar had already predicted in 1962 the possible existence of hydrogen-rich
dark objects of very low mass in the Galaxy (4) and he continued to explore further that
possibility during the 1960s. In a paper which was presented at the 1968 Symposium of
Low-luminosity Stars and published in 1969 (13) he proposed a numerical value of
approximately 0.001Msun for the minimum fragmentation mass for stars, and he then
suggested that the number of dark objects with mass below the H-burning limit in the
Galaxy is larger than that of visible stars.
MODEL ATMOSPHERES FOR LATE TYPE STARS (1962-1963)
Soon after joining NASA’s Goddard Institute for Space Studies in February 1962,
Dr. Kumar started a project for the study of the non-grey stellar atmospheres for late type
(cool) stars, and he computed, for the first time, flux-constant radiative model atmospheres
for stars with effective temperatures (Te) in the range of 2500-4000K and log g in the range
of 2.00-5.00, where g is the acceleration due to gravity at the star’s surface. These model
atmospheres were found to have many interesting properties. Some of the more interesting
results of this study are briefly discussed below:
1. The departure from greyness of the atmospheric material was surprisingly found to be
very significant. Consequently, the computation of even one flux-constant model required
a great deal of time on the Institute’s IBM 7090 computer.
2. Most of the hydrogen in the atmospheres of cool stars was found to be in molecular form
(H). This was a new result, but not totally unexpected.
3. For the first time, it was found that the free-free transitions due to H (negative
molecular hydrogen ion) contribute significantly to the total opacity in the atmospheres of
cool stars, particularly for dwarfs with effective temperatures less than 3000K.
4. A very sharp maximum at around 16,500A for the emergent continuum flux was
predicted by the computed models. This result was communicated by Dr. Kumar to Dr.
Martin Schwarzschild at Princeton University in late 1962, and, to test this prediction, the
Princeton team observed a few red giants with the Stratoscope II infrared telescope during
its second flight on November 26, 1963. Stratoscope II observations confirmed the
predicted sharp peak at around 16,500A in the observed continuum of the red giants (14)!
This prediction was also confirmed by ground-based observations (15). All of the above
results were presented at the International Astrophysics Colloquium held at Liege,
Belgium in June 1963. This paper entitled Model Atmospheres for Late Type Stars was
published in January 1964 in the Colloquium Proceedings (16).
THE EXISTENCE OF THE FIRST-GENERATION STARS IN THE
GALAXY (1961)
In a paper which was accepted for publication in the fall of 1961 and published in
1962 (17), Dr. Kumar proposed the existence in the Galaxy of a population of stars older
than Population II stars. He referred to these older stars as “first-generation” stars in this
paper. They were subsequently detected and they are now commonly know as Population
III stars. The study of Population III stars has now become a very active field in scientific
research, but it is generally not known in the scientific community that their existence was
predicted in 1961.
THE ORIGIN AND EVOLUTION OF JUPITER (1962-1974)
In late 1962, Dr. Kumar started working on the formation of planets in the Solar
System. He was particularly concerned with the origin and evolution of Jupiter. His
tentative conclusion in the early 1960s was that Jupiter was not a collapsed gaseous object
of mass 0.001Msun, and at two scientific meetings in 1966 (Conference on Low Mass
Stars at Indiana University and the Colloquium on Late Type Stars at Trieste, Italy), he
presented arguments for the formation of Jupiter (and other planets in the Solar System) by
the processes of accretion of dust and gas in the vicinity of the Sun. During the 1967-1974
period, he published a few papers in which he developed his ideas on the formation of
plants by the processes of accretion (18, 19, 20). In particular, he proposed then that Jupiter
was initially formed as a small rock and that it finally grew to its present size by the
processes of accretion of matter (dust, gas, rocks, etc.) by a solid core (the initial Jupiter).
Since 1974, Dr. Kumar has continued his work on the origin and evolution of Jupiter (and
Saturn) and this work will be discussed in a more detailed biography currently in
preparation.
BIBLIOGRAPHICAL NOTES
1. Kumar, S.S. 1962, Institute for Space Studies Report Number X-644-62-78
2. Kumar, S.S. 1962, Astronomical Journal, 67, 579
3. Kumar, S.S. 1963, Astrophysical Journal, 137, 1121
4. Kumar, S.S. 1963, Astrophysical Journal, 137, 1126
5. Hills, J.G., 1986, In Asteroids, Comets, Meteors II; Proceedings of the International Meeting, Uppsala, Sweden
6. Mennickent, R.E. et al. 2002, Astronomy & Astrophysics, 395, 557
7. Patterson, J. et al. 2005, Publications of the Astronomical Society of the Pacific, 117, 922
8. Martin, E.L. et al. 2005, Revista Mexicana de Astronomica y Astrofisica, 24, 294
9. http://galileoinstitute.org/info.html and http://adsabs.harvard.edu/abs/2003IAUS..211....3k
10. Kumar, S.S. 1969, Low-luminosity Stars (Editor: Shiv S. Kumar) (New York: Gordon and Breach Science Publishers)
11. Nakajima, T. et al. 1995, Nature, 378, 463
12. Rebolo, R. et al. 1995, Nature, 377, 129
13. Kumar, S.S. 1969, In Low-luminosity Stars (New York: Gordon and Breach Science Publishers), p. 255
14. Woolf, N.J., et al. 1964, Astrophysical Journal, 140, 833
15. Bahng, J. 1969 Monthly Notices of the Royal Astronomical Society, 143, 73
16. Kumar, S.S. 1964, Memoires of the Societe Royale des Sciences de Liege, 26, 476
17. Kumar, S.S. 1962, The Observatory, 82, 34
18. Kumar, S.S. 1967, Icarus, 6, 136
19. Kumar, S.S. 1972, Astrophysics and Space Science, 16, 52
20. Kumar, S.S. 1974, Astrophysics and -Space Science, 28, 173
21. http://galileoinstitute.org/conference.html 2012 Conference
(An account of the 50th anniversary celebration event at Ringberg castle, Bavaria, Germany on October 21, 2012 of Dr. Kumar’s prediction of brown dwarfs)