Astrophysics, Soft Matter, Climate and More

Jonathan I. Katz, Professor


[my last name]


Professor Katz adapts the following statement from Prof. Abbot (Geophysical Sciences, U. Chicago)'s web page: I practice fair judgement in all academic activities. I select people on the basis of scientific ability and promise, and I do not discriminate in favor of or against anyone based on anything else. I encourage freedom of expression and the creative exploration of ideas.

Professor Katz's work, mostly in astrophysics, also involves a number of diverse topics in applied physics, biophysics, soft matter, energy and climate. His complete publication list should be consulted for details.

Following the blow-out of the Macondo well in the Gulf of Mexico (April 20, 2010) Prof. Katz was appointed to Secretary of Energy Chu's scientific advisory panel. This experience led him to conceive a novel composition of drilling mud, involving a dilatant polymer that could make the mud viscoelastic, in order to suppress instabilities that would otherwise occur. In collaboration with Richard Garwin (also on the panel) he predicted that attempts at ``top kill'' with conventional muds would only lead to that mud being spat out the well-head with the escaping oil. This prediction was borne out when top kill was attempted and failed. Prof. Katz then organized, in collaboration with Peter Beiersdorfer and his team at the Lawrence Livermore National Laboratory, an experimental effort to test the prediction that a viscoelastic mud would not suffer such instabilities. The prediction was verified (Phys. Rev. Lett. 106, 058301 [2011]).

Prof. Katz is studying the recently discovered Fast Radio Bursts, extremely bright but brief (millisecond) sources of radio radiation. Their radiation must be emitted from very small sources, and therefore must have a very high "brightness temperature", like the most intense emission of pulsars. By applying the classical "log number-log flux" test he was able to confirm their origin at cosmological distances (and hence their great power and brightness), and with a new test, using their distribution of dispersion measures (electron column density between us and them) excluded expanding shells, such as supernova remnants, as sources of their dispersion, confirming that most of their dispersion measure results from propagation in the intergalactic medium. Despite this, the most plausible origin of Fast Radio Bursts is in the giant flares of Soft Gamma Repeaters, and he suggested a mechanism involving the excitation of plasma instability by Compton scattering of electron-positron pair annihilation radiation or by two-stream instability in a pair gap. Either may be the consequence of the sudden dissipation of magnetic energy in a neutron star magnetosphere, the most popular model of Soft Gamma Repeaters.

Prof. Katz has considered geoengineering to counteract the warming effects of anthropogenic carbon dioxide by introducing artificial scattering aerosols into the stratsophere. This is an old idea, inspired by the observation of cooling following large volcanic eruptions that loft sulphur oxides to the stratosphere where they form sulfuric acid droplets, a connection first noted by Benjamin Franklin. He has investigated the questions of determining the best material to use, the best form in which to loft it, and the best means of lofting. The tentative answers are sulfur, liquid hydrogen sulfide and rockets. In any such scheme questions of chemical kinetics arise that are not important in natural volcanic injection.

Prof. Katz has recently turned his attention to climate change. He and a series of undergraduates including Thomas Muschinski and Justin Finkel defined new measures of "storminess" and "aridity", and calculated them from NOAA rainfall data at sites in the 48 contiguous United States during the 20th Century epoch of warming. They found significantly increasing storminess at a site on the Olympic Peninsula (known for frequent steady drizzle, rather than storms). Averages over the 48 States show no significant trend, and any changes must have a characteristic time of several hundred years. Aridity is decreasing very slowly but significantly.

Prof. Katz is working on problems in boundary layer hydrodynamics. He analyzed the process of rapid adiabatic blowdown of a pressure vessel, and derived a novel dimensionless number describing the importance of buoyancy-driven circulation, resulting from the competition between conductive heating of the gas near the wall and the adiabatic cooling of the gas in the interior of the vessel. He is now working on double-diffusive boundary layers, such as those between water and glycerin or plasmas of different composition in laser-fusion targets, in which both momentum and mass diffuse, and in which the composition (affected by mass diffusion) affects the viscosity (that determines the diffusion of momentum).

In collaboration with Prof. James G. Miller of the Washington University Laboratory for Ultrasonics, Prof. Katz is developing an experimental program in the rheology of suspensions and soft matter. This follows his work on the use of corn starch suspensions as possible oil well kill fluids . A portion of this effort concerns the rheology of these suspensions. For example, they are trying to determine why aqueous suspensions of corn starch show the striking phenomenon of discontinuous shear thickening (familiar to children), while most other suspensions, including oil suspensions of corn starch, show shear thinning. This is being pursued with rheological measurements of oil suspensions, both confined and unconfined, to determine if the difference is a consequence of the different surface interactions of starch granules with oil and water. In addition, apparatus is being developed to measure the structure factor (spatial distribution) of granules in sheared suspensions using scattering of ultrasound, whose wavelengths are matched to the sizes and spacing of the granules. This microstructure determines the rheological properties of the suspensions, and is difficult to probe in any other manner.

In collaboration with the work of Prof. Miller's group on the ultrasonic properties of trabecular (spongy) bone, Prof. Katz developed a model for the mechanical properties of networks of rods connecting random nodes. This model involves the novel concept of wavelength-dependent elastic moduli, showed that trabecular bone more closely resembles foams, and offers a path towards making extraordinarily stiff porous structures. He also formulated a general model of shear thinning , a ubiquitous property of suspensions that explains why paint that is easy to spread doesn't drip.

In a more applied direction, Prof. Katz has analyzed the general problem of engineering design near performance cliffs, where small errors may produce catastrophic failure .

Some past highlights:

Invention of model of precessing accretion discs found in most mass transfer binary stars (Nature Phys. Sci. 246, 87 [1973]).

First recognition of importance and implications of X-ray sources in globular clusters (Nature 253, 698 [1975]).

Explanation of astronomical Soft Gamma Repeaters as resulting from dissipation of magnetic energy (now known as the "Magnetar" model) (Ap. J. 260, 371 [1982]).

Invention of model, later popularized by Bak as "Self-organized criticality", now applied in many branches of science (J. Geophys. Res. 91, 10412 [1986]).

First prediction of gamma-ray burst afterglows, confirmed 1997 (Ap. J. Lett. 432, L107 [1994]).


"The Biggest Bangs," J. I. Katz, Oxford U. Press (2002); is a popular book about gamma-ray bursts. To see excerpts (the Table of Contents and a sample chapter) click on your preferred format:  postscript  pdf.

Complete Publication List


High Energy Astrophysics (Addison-Wesley, 1987)

Errata for Panofsky and Phillips Classical Electricity and Magnetism 2nd ed. (Most of these are on an errata page in the Dover reprint.)

Viscoelastic Suppression of Gravity-Driven Counterflow Instability This paper by P. Beiersdorfer, D. Layne, E. W. Magee and J. I. Katz reports experiments on surrogate drilling muds shear-stiffened with corn starch. These might have enabled "top kill" of the blown-out Macondo oil well in the Gulf of Mexico in May 2010, rather than July. Also at:

Other items of possible interest, censored by WU. (Hosted at

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