Liliya L. R. Williams

Person with glasses smiling at camera

Liliya L. R. Williams

Director of Undergraduate Studies for MIfA, Professor, School of Physics and Astronomy


John T. Tate Hall
Room 285-10
116 Church Street Se
Minneapolis, MN 55455


Minnesota Institute for Astrophysics (MIfA)


Ph.D., University of Washington, 1995

B.Sc., Princeton University, 1988

Research Interests


My research centers on the role of gravity in cosmology: I use gravitational lensing and classical dynamics to study the mass distribution in the Universe, from sub-galactic to galaxy-cluster scales, with the goal of elucidating the nature of dark matter and constraining cosmological parameters. Gravitational lensing is the deflection of light from distant background sources by the intervening mass distribution, like galaxies and clusters of galaxies. Lensing is by far the best tool for the purpose of mapping out the mass distribution, as it does not rely on assumptions about the physical state of the mass. I use multiple images of distant quasars and galaxies to map out in detail the mass distribution of dark matter and ordinary matter (mainly stars) in galaxies and clusters of galaxies. Classical dynamics is a powerful means of addressing the problem of formation, evolution and relaxation of individual galaxies and clusters of galaxies. I use analytical and semi-analytical techniques to gain better understanding of dark matter halos. I am also developing theoretical models to explain the properties of dark matter halos obtained in numerical computer simulations. Our models account for the spatial and velocity distribution of dark matter within galaxy halos. They are based on fundamental physical principles, and promise to connect systems governed by Newtonian gravity with those studied by other branches of physics, like statistical mechanics and thermodynamics.

Selected Publications

  1. Barrera, B., Williams, L.L.R., Coles, J.P., Denzel, P. 2021, "Bridging the Gap Between Simply Parametrized and Free-Form Pixelated Models of Galaxy Lenses: The Case of WFI 2033-4723 Quad " Open Journal of Astroph., Vol.4, 2021.
  2. Agniva Ghosh, Liliya L. R. Williams, Jori Liesenborgs, et al. 2021, "Further support for a trio of mass-to-light deviations in Abell 370: free-form Grale lens inversion using BUFFALO strong lensing data, MNRAS," 506, 6144
  3. Gomer, Matthew R. & Williams, Liliya L.R., Galaxy-lens determination of H0: the effect of the ellipse + shear modelling assumption, Monthly Notices of the Royal Astronomical Society, Volume 504, Issue 1, June 2021, 1340–1354
  4. Zegeye, David & Williams, Liliya L.R., Two-component mass models of the lensing galaxy in the quadruply imaged supernova iPTF16geu, Open Journal of Astrophysics, Vol 3, September 15, 2020
  5. Ghosh, Agniva; Williams, Liliya L.R.; Liesenborgs, Jori, Free-form Grale lens inversion of galaxy clusters with up to 1000 multiple images, MNRAS, Volume 494, Issue 3, May 2020, 3998–4014
  6. Gomer, Matthew R. & Williams, Liliya L.R,, Galaxy-lens determination of H0: constraining density slope in the context of the mass sheet degeneracy, JCAP 11 (2020) 045
  7. Arora, Arpit & Williams, Liliya L.R., Power law pseudo phase-space density profiles of dark matter halos: fluke of physics?, ApJ 893 53
  8. Young, Anthony M.; Williams, Liliya L. R.; Hjorth, Jens, Ubiquity of density slope oscillations in the central regions of galaxy and cluster-sized systemsJournal of Cosmology and Astroparticle Physics
  9. Priewe, Jett; Williams, Liliya L. R.; Liesenborgs, Jori; Coe, Dan; Rodney, Steven A., Lens Models Under the Microscope: Comparison of Hubble Frontier Field Cluster Magnification Maps, MNRAS, Volume 465, Issue 1, 11 February 2017, 1030–1045
  10. Nolting, Chris; Williams, Liliya L. R.; Boylan-Kolchin, Michael; Hjorth, Jens, Testing DARKexp against energy and density distributions of Millennium-II halosJCAP 09 (2016) 042
  11. Woldesenbet, Addishiwot G. & Williams, Liliya L. R., Model-free analysis of quadruply imaged gravitationally lensed systems and substructured galaxiesMNRAS, Volume 454, Issue 1, 21 November 2015, 862–875
  12. Massey, Richard; Williams, Liliya, et al., The behaviour of dark matter associated with 4 bright cluster galaxies in the 10kpc core of Abell 3827, MNRAS 449 (2015) 3393
  13. Dhar, Barun Kumar & Williams, Liliya L. R., Surface brightness and intrinsic luminosity of ellipticalsMNRAS, Volume 427, Issue 1, 21 November 2012, 204–244
  14. Williams, Liliya L. R.; Barnes, Eric I.; Hjorth, Jens, Collisionless dynamics in globular clustersMNRAS, Volume 423, Issue 4, July 2012, 3589–3600
  15. Williams, Liliya L. R. & Saha, Prasenjit , Light/mass offsets in the lensing cluster Abell 3827: evidence for collisional dark matter?MNRAS, Volume 415, Issue 1, July 2011, Pages 448–460
  16. Hjorth, Jens & Williams, Liliya L. R., Statistical Mechanics of Collisionless Orbits. I. Origin of Central Cusps in Dark-matter HalosApJ (2010)
  17. Williams, Liliya L. R. & Hjorth, Jens, Statistical Mechanics of Collisionless Orbits. II. Structure of HalosApJ (2010)
  18. Williams, Liliya L. R.; Hjorth, Jens & Wojtak, Radosław, Statistical Mechanics of Collisionless Orbits. III. Comparison with N-body SimulationsApJ (2010)
  19. Rudnick, L., Brown, S., and Williams, L.L.R., Extragalactic Radio Sources and the WMAP Cold Spot., ApJ, (2007)

Default Pronouns: She/Her/Hers

Advisees & Collaborators

Graduate Students

  • Agniva Ghosh
  • John Miller
  • Derek Perera

Former Researchers and Students

Graduate Students

  • Anthony Young, (Ph.D. 2018)
  • Kevin Sebesta, (Ph.D. 2018)