Ethan O. Nadler
Galaxy formation, dark matter, and near-field cosmology
Department of Astronomy & Astrophysics, UC San Diego
Welcome!
I am an Assistant Professor at the University of California, San Diego in the Department of Astronomy & Astrophysics.
My research focuses on galaxy formation, dark matter, and near-field cosmology. A central question my group has been pursuing is whether completely dark (galaxy-free) dark matter halos exist; the answer would reveal how small-scale cosmic structure forms and provide new insight into the nature of dark matter. We tackle these problems using cosmological simulations, models of the galaxy–halo connection, dark matter theory, and observations of dwarf galaxies and strong gravitational lenses.
Building an inclusive scientific community through mentoring, outreach and community service, and teaching is important to me; my efforts in these contexts are described on the corresponding pages.
I am a co-convener of the Dark Energy Science Collaboration (DESC) Dark Matter Working Group and a member of the Satellites Around Galactic Analogs Survey (SAGA) and DECam Local Volume Exploration Survey (DELVE).
Please see my CV, publications, and media for more information!
Dark matter physics on small scales
On large scales, dark matter behaves like a cold, collisionless fluid (CDM). However, dark matter physics beyond gravity can drastically alter the abundance and internal structure of low-mass halos. Our simulations predict these signatures for observations of dwarf galaxies, strong gravitational lenses, and stellar streams. Each image below shows the same simulated Milky Way; drag the slider to transition from CDM to other dark matter models.
Warm dark matter (3 keV)
Thermal-relic warm dark matter streams freely on small scales, suppressing structure formation.
Simulations from COZMIC I; see all of our simulations.
GalaxyHalo Group @ UCSD
News
- Nov 2026The Targeted Simons Research Group on Dark Matter Dynamics is awarded, with UC San Diego as one of its nodes; it begins in January 2027.
- Jul 2026Ollie Jackson is selected for an ARCS Foundation Fellowship.
- Jun 2026Sophia Um graduates with honors after her thesis research in the group (thesis paper).
- Apr 2026Zewei Wu is selected for the LSST Discovery Alliance Data Science Fellowship Program.
- Apr 2025UC San Diego Today features AstroReach SD, which began at The Preuss School with the course Dark Matter & Python.
- Jan 2025The GalaxyHalo Group starts at UC San Diego, alongside the launch of the Department of Astronomy & Astrophysics.
Research opportunities
I am recruiting undergraduate, graduate, and postdoctoral researchers to join my group at UC San Diego. If you're interested, please email me at enadler@ucsd.edu.
About me
From 2021 through 2024, I was a joint postdoctoral research fellow at Carnegie Observatories and the University of Southern California. In 2021, I received my Ph.D. in Physics from Stanford University, where I was an NSF Graduate Research Fellow at KIPAC. In 2016, I received my B.S. in Physics from the College of Creative Studies at UC Santa Barbara.
I am passionate about interdisciplinary research. I am currently a Lattimer Research Fellow for Cross-disciplinary Explorations at UC San Diego. Earlier, I co-founded the research collective comp-syn. My interdisciplinary work is described here.