Risa Wechsler named 2022 Physical and Biological Sciences Distinguished Graduate Student Alumna

Risa Wechsler (Ph.D. Physics’ 01) has been named UC Santa Cruz’s Physical and Biological Sciences Distinguished Graduate Student Alumna. 

Each year, UC Santa Cruz’s five academic divisions—Arts, Baskin School of Engineering, Humanities, Social Sciences, and Physical and Biological Sciences—selects one graduate student alumnus/a/i as their Distinguished Graduate Student honoree. The awards ceremony for the 2022 cohort will take place on April 23 of Alumni Weekend. Risa Wechsler has been named UC Santa Cruz’s Physical and Biological Sciences Distinguished Graduate Student Alumna. 

Risa Wechsler (Ph.D. Physics’ 01) has always been interested in the biggest questions of the universe: 

How did the universe form? What is it made of? How did it evolve over the last 13.8 billion years? How did structure form in the universe? 

Those questions stayed with Wechsler throughout her academic career as she pursued an S.B. in physics at the Massachusetts Institute of Technology (MIT) and a Ph.D. in physics at UC Santa Cruz. She has since played an instrumental role in groundbreaking research in the cosmology field, with pioneering galaxy structure and cosmic structure surveys and more than 300 widely cited publications. Wechsler has also taken strides in ensuring the growth of diversity and inclusion within the physics and astronomy community.  

“One of the great privileges of being in this field is that I get to think about these really big questions every day,” Wechsler said. “The last 25 years in this field have been incredible.”

Wechsler said that it wasn’t until she began graduate school at UCSC that she truly dove into the cosmology field. She added that the years 1996-2001, while she was at UCSC, were a fascinating time to be in the cosmology field. 

“While I was in graduate school at Santa Cruz, there was a real revolution in our understanding of this question of what the universe was made of, this question of how much matter is there, and then the question of dark energy,” Wechsler said. “A lot of that got pinned down when I was at Santa Cruz, so it was a very exciting time.”

Wechsler’s research interests are focused on understanding the growth of structure in the universe, how structure formation drives galaxy formation, and how galaxies can be used to probe the fundamental physics of the universe. A majority of her work looks at the nature of dark matter and dark energy. Wechsler uses large computer simulations, physical and empirical models, and the deepest and largest galaxy surveys to determine how the universe formed and evolved.

At UCSC, Wechsler’s Ph.D. dissertation, “Dark Halo Merging and Galaxy Formation,” focused on creating simulations of the formation of dark matter halos and their implications in the universe. 

“Everything in the universe is connected to that dark matter skeleton,” Wechsler said. “The evolution of this underlying structure has implications for galaxies on all scales, from the tiniest to the largest. It has implications for understanding how black holes form and merge and how gas gets into galaxies. I love working in this area because understanding how structure evolves in the universe helps us understand how everything in the universe evolves and what it is made of."

She worked with her advisor, UCSC professor Joel Primack, with professors Sandra Faber and former UCSC Chancellor George Blumenthal. Wechsler was one of the last students to work with Blumenthal while he was a professor for her first-year project on cosmological models of dark matter halos. 

“Santa Cruz had the best of both worlds, in terms of being a strong physics department, but also having a really broad and exciting program in astronomy and astrophysics,” Wechsler said. “That definitely was one of the things that brought me there and contributed to my lifelong interest in working at the interface of theory and observations.” 

After graduating from UCSC in 2001, Wechsler pursued research fellowships at the University of Michigan and then at the University of Chicago. 

From 2014 to 2018, she was the co-spokesperson for the Dark Energy Spectroscopic Instrument (DESI) and is a founding member of the Dark Energy Survey (DES) and the LSST dark energy science collaboration. Wechsler has also played an important role in understanding the smallest galaxies in the Universe and understanding how our home galaxy, the Milky Way is connected to other similar galaxies, including through a project she leads with another former UCSC alumna, Marla Geha, called the Satellites Around Galactic Analogs ( SAGA) survey.

Wechsler is currently a professor of physics at the SLAC National Accelerator Laboratory and Stanford University. She is also the director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). Committed to public outreach and the advancement of diversity and equity, Wechsler founded an equity and inclusion committee within KIPAC, citing the underrepresentation of women and people of color not only within Stanford, but in the physics and astronomy communities as a whole. 

“I felt that there was a lot more we could be doing locally,” Wechsler said. “Being at a top department like Stanford means that when we do things, it can have a significant impact. The students we graduate often become leaders in the field. So if we’re able to not only train a more diverse set of students but also cultivate scientists who are thoughtful about how to build inclusive practices into the way we do science, it can have a real impact on the physics community.” 

In the last five years, Wechsler said the department saw a 50% increase in the fraction of women that got undergraduate degrees in physics.

“The universe is for everyone,” Wechsler said. “That’s really what motivates me every day. It’s such an amazing privilege to get to think about how the universe works and our place in it, and that motivates me to open that opportunity to more people.”