Faces of the Foundation: Chris McKee
The Hertz Fellowship changed my life,” says Chris McKee, Professor Emeritus of Physics and of Astronomy at the University of California, Berkeley and one of the first class of Hertz Fellows. Over the course of his career, McKee and his students have fundamentally changed how we understand the formation of stars and the very structure of the interstellar medium – the vast space between stars. Far from empty, the interstellar medium is full of tenuous gas at varying temperatures; it is this very gas that condenses into stars, and the properties of the interstellar medium play a critical role in understanding our universe.
In 1963, before he became a star in the field of astrophysics, McKee was a graduating physics major at Harvard with no research plans. He was considering a gap year in Germany before graduate school, but he decided to apply to the Hertz Fellowship – then in its first year – and see what happened. When he received the fellowship, and its unrestricted support, he decided to seize the opportunity to attend UC Berkeley. It was there McKee – who had not taken a single astronomy course before beginning his PhD – discovered the field that he would devote his career to.
“The Fellowship gave me total freedom to pick what I wanted to do research on,” said McKee. “I have no idea what would have happened if I had gone to Germany that year.” After his first year at Berkeley, McKee spent the summer working at Lawrence Livermore National Labs under the supervision of Stirling Colgate. “Stirling gave me a very challenging problem, and none of the top physicists I talked to at the Lab knew the answer to it. My experience that summer really got me very excited about astrophysics,” he says. He also had the opportunity to interact with Edward Teller, who, McKee says, “was probably the most brilliant person I have ever known.”
At Berkeley, McKee met George Field, who would become his thesis advisor, and began investigating whether cosmic rays – particles moving through space at near light speed, then suggested to be the result of supernovae – could indeed push through the plasma around a dying star to begin their journey through space.
On the then-cutting-edge computers at Livermore, McKee used punch cards to run simulations of plasma particles streaming past each other at relativistic velocities. His dissertation required boxes upon boxes of these punch cards. Without enough computational power to run three- or even two-dimensional simulations, McKee ran his simulations along a single dimension, the simulated plasma particles streaming in straight lines towards or away from each other. As a graduate student, McKee enjoyed the combination of computation and astrophysical thinking. Much of his research today is computational, but he now relies on others to do the computation.
After a postdoc at Caltech and three years as an assistant professor at Harvard, McKee returned to Berkeley in 1974, where he would spend the rest of his career making contribution after contribution to astrophysics. In collaboration with Princeton astrophysicist Jeremiah Ostriker, he developed a model of the interstellar medium consisting of co-existing phases of gas at three temperatures: cold (more than 200 °C below freezing), warm (thousands of degrees warmer) and hot (millions of degrees beyond that). This “three-phase model” provided the basis for decades of cosmological simulations – as the scale of these simulations increased to cover entire galaxies and more – and as a baseline for astronomical observations. “If you have a theory that provides predictions, it sharpens the questions observers can ask,” McKee says.
But McKee wasn’t researching alone. “One of the things I’ve enjoyed the most about my career is the opportunity to mentor some really outstanding students,” says McKee. One former student, Mark Krumholz, developed one of the first models to correctly predict the rate at which stars form, giving an early snapshot of the turbulent processes involved in the cloud of interstellar gas that condensed to form our Sun and, eventually, ourselves.
The expert on astronomical star formation is grateful for the effort of the Hertz Foundation to find and support future stars in science and industry. “The Hertz Foundation is a remarkable organization with an impact far exceeding its endowment because of its success in fostering the scientific leaders of the future,” he says.