Neta A Bahcall

Eugene Higgins Professor of Astronomy, Professor of Astrophysical Sciences, Director of Undergraduate Studies
pronouns: she/her/hers
Office Phone
137 Peyton

Neta A. Bahcall is the Eugene Higgins Professor of Astrophysics at Princeton University.  She is Director of the Undergraduate Program in Astrophysics, recipient of the 2024 Henry Norris Russell award of the American Astronomical Society, the 2021 President’s Distinguished Teaching Award of Princeton University, past Director of the Council on Science and Technology of Princeton University, and is an elected member of the US National Academy of Sciences, the American Academy of Arts and Sciences, a Legacy Fellow of the American Astronomical Society, Past Chair of the Astronomy Section of the National Academy of Sciences, Editorial Board member of the PNAS, and past Vice-President of the AAS.  Bahcall research interests are focused on:

  • Observational Cosmology
  • Dark Matter, Dark Energy, and the Mass Density of the Universe
  • Large-Scale Structure of the Universe; Clusters of Galaxies
  • Tracing the Cosmic Distribution of Dark Matter, Baryons, and Light
  • Formation and Evolution of Structure
  • Quasars and Their Environment; Supermassive Black-Holes

Bahcall's work focuses on addressing questions such as:  What is the large-scale structure of our Universe? How did structure form and evolve? How much dark matter exists in the Universe and where is it located? What is the nature of the mysterious dark energy? What is the fate of our Universe and its expansion? Bahcall uses different methods and a variety of tracers to answer these questions, including galaxies, clusters of galaxies, superclusters, and quasars. She combines observational data from large-scale surveys (such as the Sloan Digital Sky Survey and others) and other observations to determine the large-scale structure of the universe and its properties and compare it with those expected from cosmological simulations.  Bahcall and Soneira determination of the cluster correlation function (1983) revealed the unexpected existence of very large scale structure in the Universe, up to ~150 Mpc in scale, as well as a strongly increased clustering of clusters – confronting model expectations at that time. These results changed our understanding of the then standard cosmological models (the ‘Standard Cold Dark Matter’ – SCDM), as well as lead to the ‘biased galaxy formation’ model of structure formation.  Bahcall and collaborators’ determination of properties such as the cluster mass function and its evolution with redshift, the mass-to-light function from galaxies to superclusters and from small to large cosmic scales, the geometrical shape of clusters and of large-scale structure, have all provided powerful constraints on cosmology including one of the first determinations of the mass-density of the Universe and the amplitude of mass fluctuations.  The results revealed a sub-critical, light-weight Universe, with only ~25% of the mass needed to halt the cosmic expansion; this contradicted the then Standard Cold Dark Matter model of a critical mass-density Universe (~1980’s-1990’s). This result has now been nicely confirmed by recent observations and is part of the current standard LCDM cosmology.  Bahcall’s work helped pioneer the use of clusters of galaxies as a powerful tool in constraining cosmology -- a standard tool and methods currently commonly being used in cosmological investigations. Bahcall’s work has further explored  “Where is the Dark Matter? ” -- showing that most of the dark matter in the Universe is located in the large halos around galaxies and, unlike previous expectations, larger systems such groups and clusters are not more dark-matter dominated compared with galaxies: the total mass-to-light ratio of large systems is accounted for by the sum of the individual galaxies mass and light.  

Bahcall works closely with students and postdoctoral fellows; their work is summarized in over 300 scientific publications.  Bahcall is an elected member of the US National Academy of Sciences, the American Academy of Arts and Sciences, a Legacy Fellow of the American Astronomical Society, past Distinguished Research Chair at the Perimeter Institute for Theoretical Physics, Editorial Board Member of the Publications of the National Academy of Sciences (PNAS), past Chair of the Astronomy Section of the National Academy of Sciences, past Director of the Council on Science and Technology of Princeton University, and past Vice-President and Councilor of the American Astronomical Society.  Bahcall has been awarded the 2024 Henry Norris Russell Lectureship of the American Astronomical Society honoring ‘a lifetime of eminence in astronomical research’ --  “For her central contributions to determining the average density of matter in the universe and establishing the concordance model of cosmology, and for her dedication to astronomical education and her exemplary service to the community”,   the 2021 President’s Distinguished Teaching Award of Princeton University,  the de Vaucouleaurs Medal,  the Payne-Gasposkin Award,  the Bennet-McWiliams Award,  the Inaugural Alexander Lecturer Award,  an Honorary Doctor of Science Degree - OSU,  a Century Lecturer of the AAS, and has served as a member of various NASA, NSF, NAS, and Congressional Science committees.

Bahcall was born in Israel. She received her PhD from Tel Aviv University, working in Nuclear Astrophysics under the direction of Prof. William A. Fowler of Caltech. After receiving her PhD Bahcall moved to Princeton University in 1971.  She has served as the first Head of the Science Program Selection Office and Chief of the General Observer Branch at the Hubble Space Telescope Science Institute in Baltimore, where she helped develop the science policies for HST, including its Key Projects, science selection process, and General Observer funding; these policies, procedures, and GO funding are now adopted widely by all space missions (and some ground-based observatories). Neta Bahcall married John N. Bahcall in 1966; they have three children: Safi, Dan, and Orli – all scientists.