James Bullock
Dean, School of Physical Sciences, Professor Physical Sciences, Physics & Astronomy UC Irvine
- Irvine CA
James Bullock studies how galaxies and their constituent dark matter halos have formed and evolved over billions of years of cosmic time.
Media
Social
Biography
Aided by super-computer simulations and analytic models, Professor Bullock studies how galaxies and their constituent dark matter halos have formed and evolved over billions of years of cosmic time. By analyzing data that astronomers have collected using the Hubble Space Telescope, the Keck Observatory, and other ground and space telescopes, he works to understand how galaxies, including the Milky Way and its Local Group of galaxies, emerged from the primordial universe. One of his long-standing interests has been the use of astrophysical observations to constrain the microphysical nature of dark matter.
Professor Bullock currently serves as Chair of the James Webb Space Telescope User’s Committee. Previously he was Chair of the working group that recommended the Hubble Frontier Fields Program, which is responsible for galaxy cluster image on the top of this page. He is passionate about science outreach and appears regularly on the Science Channel’s How the Universe Works.
Areas of Expertise
Education
University of California, Santa Cruz
PhD
Physics
1999
The Ohio State University
BS
Physics and Math
1994
Links
Media Appearances
UCI celestial census indicates that black holes pervade the universe
UCI News online
2017-08-07
“We think we’ve shown that there are as many as 100 million black holes in our galaxy,” said UCI chair and professor of physics & astronomy James Bullock, co-author of a research paper on the subject in the current issue of Monthly Notices of the Royal Astronomical Society.
Galactic Features Reveal Dark Matter’s Invisible Hand
SciTechDaily online
2024-07-22
“Observed galaxies seem to obey a tight relationship between the matter we see and the inferred dark matter we detect, so much so that some have suggested that what we call dark matter is really evidence that our theory of gravity is wrong,” said co-author James Bullock, professor of physics at UCI and dean of the UCI School of Physical Sciences. “What we showed is that not only does dark matter predict the relationship, but for many galaxies, it can explain what we see more naturally than modified gravity. I come away even more convinced that dark matter is the right model.”
Explore space science at the Discovery Cube
The Orange County Register online
2024-01-28
Guests may venture out even further in the Solar System Encounter, a popular returning exhibit that features a colorful, large-scale model of the sun, planets and other objects at its center. Here, visitors may participate in space-themed experiments, find out what they’d weigh on other planets, and – new this year – view images from NASA’s James Webb Space Telescope provided through a collaboration with James Bullock, an astrophysicist and dean of UC Irvine’s School of Physical Sciences.
Dark matter does exist, simulations indicate
Futurity online
2024-04-30
“Observed galaxies seem to obey a tight relationship between the matter we see and the inferred dark matter we detect, so much so that some have suggested that what we call dark matter is really evidence that our theory of gravity is wrong,” says coauthor James Bullock, professor of physics at UC Irvine and dean of the UCI School of Physical Sciences. “What we showed is that not only does dark matter predict the relationship, but for many galaxies it can explain what we see more naturally than modified gravity. I come away even more convinced that dark matter is the right model.”
Galaxies without dark matter might be possible after all
Futurity online
2022-03-09
James Bullock, an astrophysicist at the University of California, Irvine, described how he and the team didn’t build their model just so they could create galaxies without dark matter—something he says makes the model stronger, because it wasn’t designed in any way to create the collisions that they eventually found. “We don’t presuppose the interactions,” says Bullock.
Scientists discover how galaxies can exist without dark matter
Phys.org online
2022-02-14
UCI's James Bullock, an astrophysicist who's a world-renowned expert on low-mass galaxies, described how he and the team didn't build their model just so they could create galaxies without dark matter—something he said makes the model stronger, because it wasn't designed in any way to create the collisions that they eventually found. "We don't presuppose the interactions," said Bullock.
Articles
Accurate mass estimates from the proper motions of dispersion-supported galaxies
Monthly Notices of the Royal Astronomical SocietyAlexandres Lazar, James S Bullock
2020
We derive a new mass estimator that relies on internal proper motion measurements of dispersion-supported stellar systems, one that is distinct and complementary to existing estimators for line-of-sight velocities. Starting with the spherical Jeans equation, we show that there exists a radius where the mass enclosed depends only on the projected tangential velocity dispersion, assuming that the anisotropy profile slowly varies.
A profile in FIRE: resolving the radial distributions of satellite galaxies in the Local Group with simulations
Monthly Notices of the Royal Astronomical SocietyJenna Samuel, Andrew Wetzel, Erik Tollerud, Shea Garrison-Kimmel, Sarah Loebman, Kareem El-Badry, Philip F Hopkins, Michael Boylan-Kolchin, Claude-André Faucher-Giguère, James S Bullock, Samantha Benincasa, Jeremy Bailin
2019
While many tensions between Local Group (LG) satellite galaxies and Λ cold dark matter cosmology have been alleviated through recent cosmological simulations, the spatial distribution of satellites remains an important test of physical models and physical versus numerical disruption in simulations.
Astro2020 APC White Paper: Theoretical Astrophysics 2020-2030
arXiv preprint arXiv:1912.09992Juna A Kollmeier, Lauren Anderson, Andrew Benson, Tamara Bogdanovic, Michael Boylan-Kolchin, James S Bullock, Romeel Dave, Federico Fraschetti, Jim Fuller, Philip F Hopkins, Manoj Kaplinghat, Kaitlin Kratter, Astrid Lamberts, M Coleman Miller, James E Owen, E Sterl Phinney, Anthony L Piro, Hans-Walter Rix, Brant Robertson, Andrew Wetzel, Coral Wheeler, Andrew N Youdin, Matias Zaldarriaga
2019
The past two decades have seen a tremendous investment in observational facilities that promise to reveal new and unprecedented discoveries about the universe. In comparison, the investment in theoretical work is completely dwarfed, even though theory plays a crucial role in the interpretation of these observations, predicting new types of phenomena, and informing observing strategies.
Stars made in outflows may populate the stellar halo of the Milky Way
arXiv preprint arXiv:1912.03316Sijie Yu, James S Bullock, Andrew Wetzel, Robyn E Sanderson, Andrew S Graus, Michael Boylan-Kolchin, Anna M Nierenberg, Michael Y Gurdić, Philip F Hopkins, Dušan Kereš, Claude-André Faucher-Giguère
2019
We study stellar-halo formation using six Milky Way-mass galaxies in FIRE-2 cosmological zoom simulations. We find that 5−40% of the outer (50−300 kpc) stellar halo in each system consists of in-situ stars that were born in outflows from the main galaxy. Outflow stars originate from gas accelerated by super-bubble winds, which can be compressed, cool, and form co-moving stars.
Be it therefore resolved: cosmological simulations of dwarf galaxies with 30 solar mass resolution
Monthly Notices of the Royal Astronomical SocietyCoral Wheeler, Philip F Hopkins, Andrew B Pace, Shea Garrison-Kimmel, Michael Boylan-Kolchin, Andrew Wetzel, James S Bullock, Dušan Kereš, Claude-André Faucher-Giguère, Eliot Quataert
2019
We study a suite of extremely high-resolution cosmological Feedback in Realistic Environments simulations of dwarf galaxies (Mhalo≲1010M⊙), run to z = 0 with 30M⊙ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with Mhalo≳108.6M⊙ is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field.
