Alexei M Khokhlov

Alexei M. Khokhlov was born in Moscow into the family of two prominent physicists, Vera L. Khokhlova and Moissey Z. Khokhlov. He spent his childhood at the Crimea observatory where his parents worked until he started school in 1961 in Moscow. He graduated from a well-known math school N 2 in 1971. He graduated from Moscow State University with Honors in 1980. He completed his Ph.D. in 1983 at the Institute of Applied Mathematics and started working at what is currently known as the Institute of Astronomy Russian Academy of Sciences. In 1991-1992 he worked as a Visiting Fellow at the Max-Plank Institute fur Astrophysics in Garching. Between 1992-1996 he was at the UT Austin. 1996 – 2003 he spent at the Naval Research Laboratory, and joined Astronomy Department of The University of Chicago in 2003. His scientific interests included theoretical and computational astrophysics and reactive flow fluid dynamics. His main focus is large-scale multi-dimensional numerical simulations of thermonuclear Type Ia supernova explosions. He also worked on terrestrial combustion and explosion phenomena relevant to physics of Type Ia's, such as turbulent flames and detonations. Other directions of his research were core-collapse supernovae, experiments with laser-driven and combustion-driven flows that mimic supernova phenomena, numerical general relativity, and numerical methods for adaptive integration of non-linear partial differential equations. Alexei put pursuit of knowledge above all his interests. He was intellectually curious, honest, had impeccable moral principles, and was a man of a very few words. But when he talked – the conversation was always intellectually stimulating, regardless of the topic. He was an avid reader and preferred a good book to a good movie, and a paper format to the digital reader. His book collection includes works from ancient to modern authors, from poetry to philosophy to science fiction to journalism. Alexei enjoyed hiking, biking and cross-country camping trips. Alexei loved his mighty 4Runner. He traveled US from east to west a few times visiting National and State parks. His travels were captured in numerous rolls of film and thousands of digital files. Photography was a passion he developed in his early forties. Alexei built a wet dark room equipped with everything needed for developing and printing black and white pictures. Alexei is survived by his wife of 32 years, 3 children, 2 grandchildren, and a sister. Alexei Khokhlov’s ashes will be interred on August 31, 2019 at the Flint Hill Cemetery http://www.flinthillcemetery.org/home.html in Oakton (Fairfax County). A non-denominational memorial service followed by a reception will take place at the Emmanuelle Lutheran Church https://elcvienna.org/wp/ at 10 am. The family asks in lieu of flowers consider making a donation In Memory of Alexei Khokhlov to the Baltimore Hope Lodge run by the Cancer Society. Almadena may be reached with any questions by email at : [email protected] Alexei Khokhlov's Scientific Biography Written by Professor Donald Lamb, University of Chicago Alexei Khokhlov was a world-renowned theoretical and computational astrophysicist who made significant contributions to a wide range of problems. His major scientific achievements include • Introducing the delayed detonation model of thermonuclear supernovae • Inventing a fully-threaded-tree (FTT) abstract data type for massively parallel adaptive mesh refinement computations, data compression, and scientific visualization • Formulating a scaling law and then an accurate, physics-based subgrid model for the propagation of turbulent flames in a gravitational field • Carrying out the first three-dimensional simulations of thermonuclear supernova explosions • Conducting the first 1st-principles three-dimensional simulations of deflagration-to-detonation transition in terrestrial premixed systems. • Developing a theory of gauge instabilities in 3+1 (three space dimensions plus time) formulations of general relativity • Applying cell-based adaptive mesh refinement for the first time in general relativity • Applying cell-based adaptive mesh refinement for the first time in mesoscale weather forecasting Alexei received a combined B.S. and M.S. with honors in Astronomy from Moscow State University in 1981 and a Ph.D. in Physics and Mathematics from the world-famous Institute of Theoretical and Experimental Physics and the Institute of Space Research, Moscow State University in 1984. Following graduation, Alexei was a scientist at the Astronomical Council of the U.S.S.R. Academy of Sciences from 1984 to 1991. In 1991, he left the Soviet Union for a Visiting Scientist position at the Max Planck Institute for Astrophysics in Germany. The following year he accepted a Research Associate position in the Astronomy Department at the University of Texas at Austin, working on thermonuclear-powered and gravitational-powered supernovae in Professor J. Craig Wheeler’s research group. He was promoted to Research Scientist in 1995. In 1996, he became a Research Physicist at the Naval Research Laboratory in Washington, DC, working on combustion in Elaine S. Oran’s research group. In 2003, he joined the faculty of The University of Chicago as a Professor in the Department of Astronomy & Astrophysics and the Enrico Fermi Institute, where he spent the remainder of his career. He was a member of the Flash Center for Astrophysical Thermonuclear Flashes (the forerunner of the current Flash Center for Computational Science) directed by Don Q. Lamb. Alexei is perhaps best known for his fundamental contributions to our understanding of thermonuclear-powered supernovae. These explosions are so bright they can be seen at immense distances. They are therefore a key tool astronomers use to measure distances and thereby determine the cosmological parameters of the universe. They are also a major source of the heavy elements in the Universe and the primary source of iron-peak elements. When Alexei began working on thermonuclear-powered supernovae, the canonical model was a white dwarf star with a mass near the Chandrasekhar mass limit, accreting matter from a binary companion star. As the mass of the white dwarf star gradually grows, the density in its center increases until the mixture of carbon and oxygen in its core ignites. Astrophysicists proposed that a supersonic burning wave (called a “detonation wave”) would then sweep through the star, incinerating all of the matter in it and exploding the star. However, spectroscopic observations showed that the debris of a thermonuclear-powered supernova explosion consists of both intermediate-mass elements and heavier iron-peak elements. This posed a problem for the detonation-wave model. Burning via an ordinary flame would create intermediate-mass elements but no iron-peak elements and would release far too little energy. On the other hand, burning via a detonation wave would release enough energy and create iron-peak elements. But it would create almost no intermediate-mass elements. To solve this conundrum, Alexei proposed the delayed-detonation model in which burning begins as an ordinary nuclear flame but transitions to a supersonic detonation wave, thus enabling enough energy to be released and both intermediate-mass and iron-peak elements to be produced. Essentially all thermonuclear-powered supernova models considered today are of this type. Most of the physics (the properties of matter, the nuclear reaction rates and gravity) needed to numerically simulate thermonuclear-powered supernovae was sufficiently well known at that time to enable modeling of them. The exception was the propagation of turbulent flames in a gravitational field. The initial width of the nuclear flame is a thousandth of a centimeter and the radius of the white dwarf is a billion centimeters – a dynamic range of a trillion. Direct numerical simulation of the turbulent nuclear flame in a thermonuclear-powered supernova would therefore require a computer simulation with 1036 grid points – something that is completely out of reach even today. Consequently, direct numerical simulations of the turbulent nuclear flame in a thermonuclear-powered supernova were out of the question – and still are. An accurate, physics-based “subgrid model” of turbulent nuclear combustion is therefore essential. This is exactly what Alexei provided. He first formulated a universal scaling law for propagation of turbulent flames in a gravitational field. He then showed that in the physical regime of interest the burning rate is independent of the laminar flame speed and depends only on the lateral extent of the flame. He did three-dimensional computer simulations to verify the model. In the simulations, the thickness of the turbulent nuclear flame becomes approximately the same as the width of the channel and stays that way, and the flame thickness (which governs the burning rate) is independent of the laminar flame speed, confirming the model.