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One of the last predictions of Einstein’s theory of general relativity was the existence of gravitational waves, ripples in the fabric of spacetime that distorted the distances between nearby objects. Nearly 100 years after their prediction, scientists detected the first gravitational waves from merging binary black holes in 2015, ushering in an entirely new era of astronomy. Since that first detection, the Laser Interferometer Gravitational-wave Detector (LIGO) has detected tens of merging black holes and neutron stars, with hundreds more detections expected over the next few years.

Our group is interested in the astrophysical origin of these new gravitational-wave sources. Using a combination of high-performance computing simulations, semi-analytic statistics, and analytic theory, we explore how binary black holes and binary neutron stars can form and merge within the age of the universe. We want to answer questions like: does the rate of gravitational-wave mergers change in different parts of the universe? Do the masses and spins of LIGO’s binary black holes suggest one origin, or many? Are all of LIGO’s binaries on circular orbits? Can gravitational waves tell us about the lives of the galaxies they come from, and about the expansion of the universe itself?

There are many proposed astrophysical pathways to merge two compact objects. We focus in particular on the ways in which stellar dynamics, the movement of objects due to their mutual gravity, can form binaries with unique observational properties (including the large masses of the black holes observed by LIGO, Rodriguez et al., 2015). These simulations of massive star clusters use high-performance parallel computing techniques to solve the gravitational N-body problem. Broadly, our group is interested in the formation, evolution, and destruction of these star clusters in their host galaxies across cosmic time. These include not only open and globular star clusters, but also the nuclear star clusters in the centers of galaxies, the homes of the largest supermassive black holes.

Image of the globular cluster 47 Tuc. Dense cluster of stars on a black background.
The Globular Cluster 47 Tuc (NGC 104), captured by the VISTA instrument at the Paranal Observatory in Chile.

More recently, the Rodriguez group has been working on the evolution of massive stars, specifically the progenitors of black holes and neutron stars. This has included new work on the production of detached black hole-star binaries (such as the recently detected binaries in Gaia, as well as the known systems in NGC 3201). We have also begun to work on galactic archeology, understanding the dynamics of stars and star clusters in broader galactic and cosmological context.