Research

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.

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