Christof Litwin, a theoretical physicist with broad interests ranging from field theory to plasma physics and astrophysics, passed away suddenly and unexpectedly on 4 October 2001, from complications arising from surgery for oral cancer. Christof was a senior scientist at the University of Chicago, working within the Department of Astronomy and Astrophysics and the Center for Astrophysical Thermonuclear Flashes.
Christof’s life and career mirror those of many European scientists who lived through the turmoils of the 20th century. He was born in Lodz, Poland on 15 June 1949. His father, Jacob, was a history professor while his mother, Eugenia, was a pediatrician. Christof received his pre-college education in Lodz and in Warsaw. However, to escape anti-Semitic strains which were prevalent in Poland at the time, the family moved to Sweden. To further his education in physics, Christof immigrated to Denmark. Because he had shown his talent in physics early in Poland, Christof received strong recommendations for study at the University of Copenhagen, where he enrolled, and received his Part I degree in Mathematics-Physics in 1972, and his Cand. Scienti. in Theoretical Physics from the Niels Bohr Institute in 1976. His thesis title was “Dual Strings and Membranes,” an early foray into string theory. After a postdoctoral period in the United States, he completed further requirements for his degree at Copenhagen, receiving his ScD in Physics in 1990.
Christof’s postdoctoral training started in particle physics at Stanford University. From 1977 to 1980 he was a Research Fellow at SLAC, but he realized that his interests were turning to collective phenomena. He switched fields and became a research associate at the Cornell University Laboratory for Plasma Studies, where he worked closely with Ravi Sudan from 1980 to 1984. While at Cornell, Christof investigated a range of plasma problems, including the stability of the spheromak magnetic confinement configuration and turbulence and stability of tandem mirrors.
In 1984 Christof moved to the University of Wisconsin at Madison, where he stayed until 1996, performing seminal work in the departments of Physics and Engineering Physics on the effect of the ponderomotive force on the macrostability of a plasma. Christof’s ideas invariably led him to interact strongly with experimentalists. He significantly influenced experiments at Wisconsin and elsewhere, some of which, e.g. a lower-hybrid wave injection experiment, are just now beginning.
The Wisconsin period did have one interruption: Christof served as a visiting associate professor in the Department of Nuclear Physics at the Weizmann Institute from 1989 to 1991. The trip to Israel was a signal event in Christof’s life in two ways. It was there that he met his wife-to-be, Adi Altshuler. It was also at the Weizmann Institute that he began to pursue the third area of his physics interests, plasma astrophysics. Near the end of his stay in Madison, Christof spent some time at the University of Chicago as a visiting assistant professor teaching a course in plasma astrophysics in the Department of Astronomy and Astrophysics. He then made his final switch in field—to astrophysics—and in institution in 1997, when he became a senior research associate at the University of Chicago.
It was characteristic of Christof that he did not start with trivial problems: he realized that his plasma physics background could be put to good use in solving a significant solar-physics problem. His choice as an entry problem was the transport processes in the solar corona that give rise to the observed highly structured magnetized atmosphere. Christof quickly worked out the consequences of existing laboratory-based transport theory for the solar corona and, in a landmark and often-quoted paper published in 1993 in the Astrophysical Journal, he provided a framework for further studies of this problem. His work continues to this date to define the research agenda in this field.
Although Christof continued to work, and publish, on the solar corona, he branched out to other fields. His publications in astrophysics included studies of the stability of accretion columns on neutron stars, the penetration of accreted plasma into the magnetosphere of compact stars, the acceleration of ultra-high-energy cosmic rays (UHECRs) due to cometary or asteroidal impacts in the magnetospheres of neutron stars, and the interaction between stellar magnetospheres and surrounding accretion disks. All of these studies bore the hallmarks of Christof’s science: they focused on hard problems, and they proposed truly novel solutions.
What is not so evident from the paper record is the enthusiasm that Christof brought into his work, the inquisitive spirit, the nonconforming and always questioning attitude, and the Talmudic style of research. Those of us who worked closely with Christof can never forget his constant reexamination of calculations and of ideas—of things we thought had been fully resolved but Christof could not leave be.
Christof’s achievements were recognized by his peers: he was named a NATO Fellow in Science (1977-1979) and was elected a Fellow in the American Physical Society in 1996. Even while hospitalized just before his death, Christof could be found actively engaged, as usual, in a wide variety of calculations, including the treatment of magnetic stochasticity on Alfven wave propagation and current drive in laboratory plasmas, and new computations of the propagation of UHECRs in the intergalactic medium. He had even set up his computer in the hospital room, and was busy responding to his email.
Christof possessed an unusual appreciation for the pleasures of life and a gentle wisdom about it, which he generously shared with his friends and colleagues. Speaking six languages, he had a love of conversation and literature. He leaves behind his wife Adi, an attorney and Director of International Programs at the Northwestern University Law School, their two young children, Yael and Yonatan, his mother, and his brother.
We miss him deeply.