Articles and Interviews in the Popular Media

Before the early 1970's most astronomers shared an unstated assumption that almost all of the mass in galaxies resided in visible stars. Ostriker was important in convincing the astronomical community that this natural and seductive assumption is wrong, by advocating a radical new model for galaxies in which the system of visible stars is only a minor component at the center of a much larger halo of dark matter of unknown composition. This thirty-fold expansion of the scale and mass of galaxies was the grandest revision in our understanding of galaxies since Shapley's work at Harvard in the early 1900's, and, after considerable initial skepticism, has now largely been confirmed by observations.

Ostriker's research also focused on the gaseous interstellar medium, the birthplace of stars. The complex self-regulating interactions that we see around us between living organisms and the local environment are echoed in the interactions between stars and the interstellar medium. By analyzing the interstellar medium as a self-regulating system, Ostriker and his coworkers showed how the energy inputs from stellar ionizing radiation and powerful supernova explosions sculpt interstellar matter into the complex multiphase medium we see around us in the Galaxy, which in turn determines the rates of formation of new stars. Ostriker's work helped clarify the dynamics and evolution of supernova remnants, the role of cloud evaporation in the interstellar medium, and the processes by which supernova shock waves accelerate cosmic rays. His conclusions have been extended to the intergalactic medium, in particular to the study of intergalactic gas clouds and their role in the formation of galaxies.

Ostriker worked in the development of sophisticated numerical simulations of the evolution of the early universe and the formation of structure in cosmology, including galaxies, clusters of galaxies, and the intergalactic medium. The Ostriker and Steinhardt concordance model (a flat universe with a cosmological constant) has received strong recent support from observations of distant supernovae and fluctuations in the cosmic background radiation.

Ostriker’s primary research work is in computational cosmology. He is also active in the computational aspects of galaxy formation and black hole interactions with their environment. The basic algorithm used for the Millenium Simulation and many other cosmological investigations – the Tree Particle Mesh (“TPM”) algorithm – was developed at Princeton under his guidance. He has worked with Paul Bode on matching very large N-body simulations to astronomical observations as a way of determining the best fit cosmological model and helping to establish the Lambda Cold Dark Matter model as the standard. His work with Ren-Yue Cen pioneered the large scale study of where and when galaxies are formed and also helped to elucidate the “missing baryon” problem, ie the finding that most of the ordinary chemical elements are, at the current epoch, to be found in several million degree intergalactic gas. In his work with Thorsten Naab and other collaborators he has shown that relatively simple physics (eg “gravitational heating”) dominates the formation of massive galaxies, that the early transformation to the “red and dead” state is to be expected and that flat rather than peaky rotation curves are expected, but that quite high numerical resolution is required before these facts are apparent. Finally, in his work with Lucca Ciotti and other collaborators he has shown how massive black holes at the centers of galaxies can regulate their own growth and the bursts of star-formation in the centers of the parent systems.

He has and continues to serve on advisory committees for high performance computing at NSF headquarters, and the Pittsburgh and NCSA supercomputer centers, as well as establishing the Princeton Institute for Computational Science and Engineering and serving as its Director of in the period 2005-2009.



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