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A Quiet Maverick Sees a Different Sun
Volume 5, Issue 7 - April 4, 2001
 

A Quiet Maverick Sees a Different Sun

Carl A. Rouse is a quiet maverick of an astrophysicist whose "nonstandard" models of the interior of the Sun have been provoking the solar physics community for nearly 40 years.

In 1962, while working at the Lawrence Livermore National Laboratory, the Caltech-trained scientist got interested in pulsating variable stars, of which the best-known are the Cepheids. The cyclic radial motions observed in some of these stars far exceed the oscillations of our own Sun (which were then unknown). "I thought that this nonlinear hydrodynamic motion must be due to the nonlinear effects of ionization and excitation of the atoms in the atmospheres of these stars," Rouse recalled. To test his ideas, he developed an "equation of state" appropriate for highly ionized gases and employed this in a computer code developed by colleagues for modeling supernovae.

His modeling was able to reproduce the observed variation in star pulsations, but Rouse soon began to ask the next question: "What is the equilibrium structure of a typical variable star?" In other words, what's going on inside? And what is varying?

"The rest is history that is still developing," Rouse said. Because one way to get at his questions was to consider variation from the interior structure of the Sun, which was then thought to be well known, Rouse began looking into what had been done about solar modeling (at that time, very little). There were several versions of a "standard solar interior" model, derived from estimates of the Sun's central temperature and density, knowledge of the relative abundances of hydrogen and helium in the solar atmosphere, and reasonable guesses at the internal abundances.

But when Rouse used his own equation of state and all the usual assumptions about interior composition, he couldn't even get the Sun to emerge from the modeling with the right mass, luminosity and radius (these properties, at least, have been known quite accurately for a very long time). If the equation of state was reasonable, perhaps there was something wrong with the usual assumptions? Through a long series of jobs doing more applied research, first for Lawrence Livermore National Laboratory, then at the Naval Research Laboratory in Washington, D.C., and, by 1968, at the small company north of the UCSD campus that is today called General Atomics, Rouse attacked his solar puzzles on his own time.

An Iron Core in the Sun?

In 1963, Rouse found that his models fit the available information better if he used a different elemental composition for the Sun. In particular, the models worked well when Rouse assumed a small core region in the center of the Sun composed of material with a higher atomic number (Z) than hydrogen or helium -- what he called "a high-Z core." Since high-Z materials are thought to be produced only in supernova events, postulating such a core has implications for theories of solar formation as well as solar composition. One likely candidate element for such a core is iron, and Rouse's theory has been referred to (by him and others) as the idea of a solar "iron core."

Rouse's idea that the sun may have a high-Z core has been considered pretty wild by most solar physicists, not simply because his career path has made him a kind of "outsider" in the solar physics community: the main objection has been to the implications his theory has for the formation of the Sun. The solar system is commonly thought to have formed about 4.5 billion years ago from a homogeneous, well-mixed protosolar nebula, 71 percent hydrogen, 27 percent helium, and only 2 percent heavier elements. Rouse's theory implies a more inhomogeneous core of solar system formation, perhaps containing clumps of high-Z elements formed locally in some previous supernova.

But his colleague Joyce Guzik, a solar modeler at Los Alamos National Laboratory, said, "Dr. Rouse's methods are independent of or different from the ones used by most researchers, but his approach is still valid and reasonable. If he gets the same results by different methods for the interior structure of the sun, we are reassured about the correctness of our models. If Dr. Rouse obtains different results -- as he sometimes does -- we are challenged to understand and track down the reasons for the differences, which often leads us to new insights."

During all this time, the field of solar physics itself has changed utterly. Rouse's solar modeling, carried on for the past 15 years at SDSC, has been catching up with and then questioning the "conventional wisdom" as that itself has shifted. Beginning with the original SDSC Cray X-MP and continuing through a succession of machines to today's Cray T-90 and T3E, Rouse has used comparatively small amounts of time with progressively more efficient models that have nevertheless been judged appropriate for use on the allocated computational resources.

Neutrino Oscillations?

In 1967 a new solar puzzle appeared. Theories of the thermonuclear burning going on at the center of the Sun predict a certain outflow of nearly massless particles called neutrinos. But when Raymond Davis and colleagues built the first neutrino detector, a tank of cleaning fluid at the bottom of South Dakota's Homestake Mine, they saw fewer than a third of the predicted neutrinos.

Theorists soon provided a flurry of explanations for the undercount. The solar neutrino deficit is still one of the great unsolved problems of solar physics. A summary of the state of this science appeared recently in the CERN Courier.

One of the leading theories suggests that neutrinos of different types ("electron, tau, and muon") may oscillate back and forth between types, thus lowering the count for the more easily detected types. But Rouse points to a recent experiment carried out by Caltech scientist Felix Boehm and colleagues at the Palo Verde nuclear reactor (reactors are also neutrino sources) in which no oscillatory behavior was detected (results published in Physical Review D 84: 3764-3767, last April). There are now eight or nine neutrino experiments at reactors and particle accelerators and twice as many underground experiments, including three being conducted under the ice of the Antarctic, all in pursuit of the truth about the full spectrum of neutrinos. Rouse's small, high-Z, iron-like solar core is in contention as another way to account for the neutrino deficit, and he points out that his models are consistent with the results of the major neutrino experiments.

Helioseismology

Still another way to get at the interior structure of the Sun has arisen over the past 20 years. Called helioseismology, after the methods of seismology used to determine the internal structure of the Earth, it is the study of solar oscillations. Simple periodic oscillations of stars have been observed since the eighteenth century, and such oscillations had attracted Rouse to his original investigation. But helioseismology took off in 1960, after the identification by physicist Robert Leighton of a strong 5-minute oscillation of the Sun.

Helioseismology is now in its fifth decade and has become a minor industry, studying wave motions that are excited and can propagate within the Sun. Experiments include both ground-based (GONG, the Global Oscillation Network Group) and space-based (SOHO, the Solar and Heliospheric Observatory) monitoring. Both forward and inverse analysis of the experimental information has led to numerous revisions and re-revisions of theories of the solar interior.

Rouse lost no time in incorporating helioseismic information in his models, and at present his modeling can reproduce the observed spectrum of oscillations when a high-Z core is included.

"The time I have received for my computations at SDSC has been invaluable in helping me to keep up with the rapid tempo of discovery in the field of solar physics. My approach is so computationally intensive, solving the full set of solar equations from center to surface, that it would be impossible without the supercomputer time," Rouse said.

Who is Carl Rouse?

Rouse's own history is as unusual as the solar interior he derives from his calculations. He is that rarest of creatures, an older African-American scientist. He was born in 1926, one of seven children of a Youngstown, Ohio, steelworker and auto mechanic. After high school and two years in the Army at the end of World War II, during which he had been sent to two separate engineering courses, Rouse returned to Youngstown to work for the county government as a draftsman. In the meantime, he applied to attend several universities on the GI Bill.

At the Case Institute of Technology in Cleveland (now Case Western Reserve University), Rouse earned a bachelor's degree in physics with a math minor (1951). From there, he was admitted to the California Institute of Technology, where he earned a master's degree in physics (1953) and became the student of Eugene W. Cowan, who was then in the Cosmic Ray group formed by Nobelist Carl D. Anderson. Under Cowan, Rouse performed experiments using a cloud chamber and developed a detector to select interesting events for further study. He earned his doctorate in physics, again with a minor in math, from Caltech in 1956.

While working at General Atomics, Rouse was awarded a patent for improving the material used in shielding nuclear power reactors, and he edited a number of books on high-temperature physics. In 1992, he "retired" to found his own research and consulting firm, Rouse Research, in Del Mar, California.

Rouse has presented his modeling work at scientific meetings (to which he often travels at his own expense), and his papers on solar topics have been published in the main astronomical and solar physics journals. He is a member of the National Society of Black Physicists, which met at Stanford University on March 31 and gave him the Elmer Imes Award "for outstanding and sustained excellence in research." He is also a Fellow of the American Physical Society and a member of the International Astronomical Union and the American Astronomical Society. His biography has appeared in a 1996 volume titled Distinguished African American Scientists of the 20th Century (Oryx Press).

Rouse, now 74 years old, is still tackling the problems with youthful enthusiasm. He spoke excitedly about the next set of parameters he hopes to incorporate in his models. "It's just physics," he said. "If we know certain facts and the chemical abundances of the elements in the Sun at a given point along the solar radius, we should be able to figure out all the rest, if our computers are fast enough."

He remains a maverick, with quiet persistence. As John Harvey of the National Solar Observatory, editor of the journal Solar Physics, said when asked what the community should do with its mavericks, "We should cherish them." --MM

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