| I'm an observational astronomer who focuses on the Milky Way and nearby galaxies. My research interests are pretty broad, covering everything from exoplanets to dark matter. One of my consistent areas of emphasis has been the dwarf galaxies orbiting the Milky Way, which are the oldest, least chemically evolved, and most dark matter-dominated stellar systems currently known. Current projects include: |
| Over the past 20 years, more than 50 new Milky Way satellite galaxies and candidates have been discovered. Along with many collaborators, I aim to measure the masses, chemical composition, ages, and orbits of these objects so that we can use them to learn about dark matter and galaxy formation. |
| Galaxies follow a relatively tight correlation between their stellar mass (or luminosity) and metallicity, as shown most clearly by Christy Tremonti, Evan Kirby, and others. For the very tiniest galaxies with masses below a few thousand solar masses, this correlation appears to break down. My collaborators and I are obtaining improved metallicity measurements in this regime to better understand this behavior. |
| Ultra-faint dwarf galaxies have been extensively studied since 2005. The more compact stellar systems with similar luminosities but smaller radii, called ultra-faint star clusters or ultra-faint compact systems, have been largely ignored (which is at least partially my fault!). There is now evidence emerging that some of these objects could in fact be dark matter-dominated dwarf galaxies, but better observations are needed to confirm this possibility. |
| The exquisite astrometry and spectroscopy from the Gaia satellite make it possible to find black holes in wide binary systems where the companion is an ordinary star. These systems can provide some of the first insight into the Milky Way's black hole population beyond the few dozen X-ray binary systems in which black holes are actively accreting matter from their companion stars. My collaborators and I are using Gaia DR3 data to investigate and confirm black hole candidates. |
| The host stars for most known exoplanets are metal-rich and relatively young, both because those stars have higher planet occurrence rates and because searches have consequently tended to focus where they are most likely to produce positive results. Metal-poor stars are intriguing as planet hosts for several reasons: they can provide insight into planet formation models, they can allow studies of how planet properties change as a function of the available chemical elements, and their planets are the oldest in the Galaxy. My collaborators and I are trying to significantly expand the sample of exoplanets in the metal-poor regime. |
| I was at Las Campanas Observatory observing with the Magellan-Clay Telescope on August 17, 2017. I was therefore able to obtain the first spectrum of the neutron star merger event GW170817/AT2017gfo (as well as the earliest blue photometry of the source). Based on that experience, and combined with my interest in r-process nucleosynthesis from the metal-poor star perspective, I have continued to be involved in Carnegie's gravitational wave followup efforts for additional binary neutron star candidates (e.g., S240422ed, S250206dm). |
| I worked for Jeff Willick on a project called Shellflow, in which we were trying to determine whether the mass causing the Local Group to move with respect to the rest frame of the universe is within about 85 megaparsecs of us or not. If you have a Postscript viewer, you can take a look (be warned: it's a big file). |