Autobiography of Steven Balbus
I was born in Philadelphia in 1953 and attended the William Penn Charter School for my secondary education. I was particularly drawn to mathematics. In my last year in high school, I was excused from these classes. I also developed an interest in astronomy, then a sort of hobby.
In 1971, I entered the Massachusetts Institute of Technology. I thoroughly enjoyed my experience. I was much taken with my applied mathematics and physics courses, and elected to double major in these two subjects. I still followed astronomy at the Scientific American level, so at the conclusion of my undergraduate studies I decided to continue in theoretical astrophysics, a natural union of all my interests.
My PhD studies were undertaken at the University of California, Berkeley. The thesis work was guided by Christopher McKee, whom I held, and continue to hold, in the highest regard. The Astronomy Department in Campbell Hall hosted at that time a cadre of brilliant postdocs, many of whom would ultimately dominate their fields. For a graduate student, it was a daunting but exhilarating experience. I completed my thesis in 1981 on the fate of cool interstellar gas clouds embedded in a very hot ambient plasma. The thesis involved some knotty challenges that took a long time to understand, and impressed upon me the subtlety that often attends problems in astrophysical fluids.
After formative postdoctoral appointments at MIT and Princeton, in 1985 I accepted a faculty offer from the UVa. I became fascinated by the thermal stability behavior of X-ray emitting gas, then a University of Virginia specialty. In the course of my studies, I found that cooling in a magnetized gas was very different from an unmagnetized gas, even if the field is quite weak. This was surprising, and made a deep impression upon me.
John Hawley arrived at the UVa in 1987. We got on well from the start, and began collaborating. John had a definite idea about what constituted the best topic to be working on: accretion disks. I was no stranger to disk dynamics, having done calculations on gas in spiral galaxies during my postdoc. In 1990, John showed me a paper in which a wave propagating through a disk amplified a magnetic field. The wave itself, however, was not allowed to be altered by the field. Based on my thermal studies, I was unconvinced by this approach. So I worked the problem from scratch, including the magnetic field self-consistently, and after sorting out some conceptual puzzles, discovered something peculiar. An additional, highly unstable, mode appeared. Subsequent literature searching showed that others had started down this route, but in a very opaque manner. The significance had not been grasped at all. In 1990, the unstable mode had no name. It is now known as the magnetorotational instability (MRI), and has become part of the astrophysical landscape.
Having played a key developmental role, John possessed one of the few magnetohydrodynamic codes in the world. He was able to verify the analysis and then led the way in showing that the outcome of the instability was turbulence. The origin of accretion disk turbulence had been a longstanding astrophysical puzzle, and we were both tremendously excited. We now understood the physics of why simple disk orbits broke down, and could both simulate and visualize the turbulence. Our combination of skills put us in a unique position to give substance to notions that previously had been speculation and phenomenology, laying the groundwork of a new field. Indeed, the MRI goes beyond accretion disks, it proved to be a whole new window on the dynamics of weakly magnetized astrophysical gases. I was thus able to spend several happy years working on progressively more ambitious studies of this type of problem with students and postdocs.
In 2004, I moved to the Ecole Normale Supérieure in Paris, France. It meant having to break a close working relationship with John, but personal events had intervened. Two years earlier I had married Caroline Terquem, a French astrophysicist. Now a position had come my way at the ENS, a renowned institution up the street from the Institut d’Astrophysique de Paris, where Caroline worked. Shortly after arrival, I was awarded a Chaire d’excellence by the French Ministry of Higher Education, which supported my work generously. I was able to purchase a cluster for large scale simulations and to hire several excellent postdocs. My work focused on the dynamics of protoplanetary disks, magnetic Prandtl number effects in turbulence, and pursuing thermal analogues of the MRI with heat playing the role of angular momentum. Later, I became something of a solar astronomer, developing with colleagues a novel approach to understanding important features of the Sun’s internal rotation.
In the autumn of 2012, I moved to Oxford University to take up the post of Savilian Professor of Astronomy, succeeding Joe Silk in this ancient and venerable Chair. Caroline also secured an excellent position at Oxford. We were both delighted with this turn of events, together with the many opportunities it afforded.
It has been my good fortune to have worked with exceptional mentors, colleagues, postdocs, and students. They say that fortune favors the prepared mind, but I have little doubt that much of what I have been able to accomplish has been strongly influenced by interacting with these individuals. This occasion is just the moment to thank them from the bottom of my heart.
23 September 2013 Hong Kong