In 1985, the UA Theoretical Astrophysics Program (TAP) was created based on the shared vision of Jack (Randy) Jokipii and the then-heads of the astronomy, physics, and planetary sciences departments. The aim was to combine evident faculty and departmental strengths to create a theoretical program that would complement the UA’s recognized strengths in observational astronomy and planetary sciences. Since inception, the State of Arizona has continued to provide annual funding which has supported development of this tightly integrated program and increased the growth and visibility of the UA’s leadership in the area of theoretical astrophysics.


The Departments of Astronomy, Physics, and Planetary Sciences form the Theoretical Astrophysics Program along with key partnerships with Applied Mathematics and the National Optical Astronomy Observatory (NOAO). Membership is open to all UA faculty, research partners, postdocs, and grad students interested in the field of theoretical astrophysics. Several TAP faculty affiliate members are also recognized members of the National Academy of Science: David Arnett, Randy Jokipii, and Renu Malhotra.


Each year, the TAP offers colloquia covering a broad range of current research topics given by early career scholars as well as senior faculty. TAP also awards the Graduate Student Research Prize to one UA grad student or recent Ph.D. with the winning submission selected for research quality and originality. The TAP Small Grants Program provides limited funding to TAP members to support research-related travel expenses, equipment purchase, research dissemination, etc.

Credit: T.A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF)

Steering Committee

The TAP is directed by a Steering Committee composed of six members and a chairperson with member representation equally distributed across the departments of physics, astronomy, and planetary sciences. The steering committee is responsible for making significant program decisions, including program funding priorities and allocations, selection of student prize recipient, new member applications, and general planning of annual program priorities and directions.

Dimitrios Psaltis, Chair

Professor, Steward Observatory
Dr. Psaltis’ research focuses on the physics of neutron stars and black holes, the properties of magnetohydrodynamic turbulence in accretion flows, the testing of the theory of general relativity in the strong-field regime, and the physics responsible for the accelerating universe.

Areas of Interest:

Theoretical High Energy Astrophysics, General Relativity, Computational Astrophysics.

Erik Asphaug

Professor, Lunar and Planetary Laboratory
Dr. Asphaug specializes in planet formation resulting from pairwise collisions (‘giant impacts’) and the physics of low-gravity bodies such as comets, small satellites and asteroids. He dabbles in the evolution of the martian and lunar surface, and the origin of chondrules. Dr. Asphaug is currently pursuing the development of laboratories in near-Earth space relevant to accessing and processing in situ resources, and missions to asteroids and comets.

Gurtina Besla

Assistant Professor, Steward Observatory

Dr. Gurtina Besla’s research focuses on the formation and evolution of low mass dwarf galaxies. Through numerical simulations, Dr. Besla explores the impact of gravitational interactions on the observed properties of low mass galaxies in various environments. Dr. Besla is a world expert in the study of the closest example of an interacting pair of dwarf galaxies, the Large and Small Magellanic Clouds. Dr. Besla’s research on these galaxies has overturned conventional wisdom, illustrating that the Magellanic Clouds are likely recent interlopers in our neighborhood rather than long term companions to our Galaxy.

Sam Gralla

Assistant Professor, Physics

Dr. Gralla works on the theory of strong gravitational and electromagnetic fields, as occur near black holes and neutron stars.  While most of his research is astrophysically motivated, he also ventures into more theoretical territory like black hole thermodynamics

Kristopher Klein

Assistant Professor, Lunar and Planetary Laboratory

Dr. Klein’s research focuses on studying fundamental plasma phenomena that governs the dynamics of systems within our heliosphere as well as more distant astrophysical bodies. He has particular interest in identifying heating and energization mechanisms in turbulent plasmas, such as the Sun’s extended atmosphere known as the solar wind, as well as evaluating the effects of the departure from local thermodynamic equilibrium on nearly collisionless plasmas which are ubiquitous in space environments.

Shufang Su

Professor of Physics, Department of Physics

Fields of Study: Astrophysics and Cosmology and High Energy Physics

Research Interests: Theoretical elementary particle physics focusing on new physics beyond Standard Model. Phenomenology of new physics models, collider searches, Higgs physics, electroweak precision studies, dark matter and particle cosmology.

Andrew Youdin

Assistant Professor – Astronomer, Steward Observatory

Dr. Youdin is a theoretical astrophysicist whose primary focus is the formation and evolution of planetary systems. He employs various techniques, including analytic derivations, statistical data analysis and detailed numerical simulations. Current research topics include planetesimal formation, giant planet formation, exoplanet statistics and atmospheres, circumbinary dynamics, and accretion disks. His work on the streaming instability, a mechanism to concentrate planet-forming solids in disks, has transformed the modern understanding of planetesimal formation. Dr. Youdin investigates a range of planet formation mechanisms with an eye to ongoing breakthroughs in exoplanet, disk and Solar System observations.

Contact staff with any questions/concerns:

Rosie Johnson

Project Manager
Steward Observatory, Room N334A


Debbie Federico

Administrative Staff
Steward Observatory, Room N334