LIGHTING UP THE DARK: WHERE IS THE ? Neta A. Bahcall

4:30 p.m., Tuesday, Nov. 11, 2014 Rashid Auditorium Gates & Hillman Centers Neta Bahcall uses different methods and a variety of tracers including , clusters of galaxies, Free and open to the public superclusters and to answer fundamental questions about the structure of the universe. In Reception to follow work summarized in over 300 scientific publications, Bahcall and her colleagues have provided powerful How is dark matter distributed in the universe? How does it relate to the distribution of light, constraints on including one of the first stars and baryons? These questions are examined using gravitational lensing and other recent determinations of the mass-density of the universe and observations that trace the distribution of mass in the universe from small to large scales and of the amplitude of mass-fluctuations. reveal the connection between the dark and bright side of the universe. Born in , Bahcall received her Ph.D. from While the halos of dark matter around galaxies show an observed mass distribution that is . She later moved to Princeton considerably more extended than that of light, this trend changes on larger scales, where the University where she is now the Eugene Higgins mass, light and stars trace each other remarkably well. This indicates the ‘edge’ of the dark matter Professor of . In her research, Bahcall distribution. The measurements suggest that most of the dark matter in the universe may be works closely with students and postdoctoral fellows. located in large halos (~a million light-years) around galaxies, and with no significant increase She is director of the undergraduate program in in the dark matter component on larger scales. The mass of groups, clusters and large scale astrophysics, and past director of the Council on structure appear to be mostly just the total mass of the individual members, including Science and Technology of Princeton University. Her their extended halos, plus gas. The stellar mass fraction is constant on these large scales, with honors include the Payne-Gaposchkin Award and stars comprising only about one percent of the total mass. How can stars follow the total membership in the National Academy of Sciences and mass so well? And where are the rest of the baryons? The connection between baryons, stars the American Academy of Arts and Sciences. She is a distinguished research chair at the Perimeter Institute and mass on these scales will be discussed, as well as the implications for cosmology, galaxy for Theoretical , a member of the editorial formation and the mass-density of the universe. board of PNAS, and past vice-president and century lecturer of the American Astronomical Society. She also served as the first head of the Science Program Selection Office for the .