Research
Giant Planet Dynamics and Demographics
Thousands of exoplanets have been discovered in recent decades, with many exhibiting properties unlike the planets in our solar system. Giant planets at large distances from their host stars (“cold Jupiters”) tend to have much higher eccentricities than the nearly circular orbits of the solar system giants. The presence of many giant planets on short-period orbits (“hot Jupiters") has also been challenging to explain due to the hostile conditions for giant planet formation near stars. High-eccentricity migration has been proposed as a solution to both of these puzzles, in which an initially cold Jupiter is excited to high eccentricities before being tidally dragged onto a short-period orbit. However, the dynamical mechanisms responsible for this process remain unclear. Secular perturbations from an inclined stellar companion are a potential source of eccentricity oscillations, a phenomenon known as the Eccentric Kozai-Lidov (EKL) mechanism. To explore this problem, I have performed simulations of cold Jupiters in stellar binaries that show the eccentricity distribution produced by EKL is consistent with observations, suggesting that this mechanism indeed plays an important role in sculpting the population. I have also developed analytical models to describe the EKL-driven descent of a giant planet in a stellar binary (these models are applicable to hierarchical three-body systems on all scales!).
Cold Jupiter eccentricities: Weldon et al (2024), arXiv:2411.05066
Analytical EKL models: Weldon et al (2024), ApJ 974 302
Supermassive Black Hole Accretion
High-resolution observations of the Milky Way’s Galactic Center over the past two decades have revealed a population of stars orbiting a supermassive black hole (a discovery that earned UCLA Professor Andrea Ghez the 2020 Nobel Prize in Physics). Sgr A* is the variable electromagnetic source associated with accretion of hot plasma onto the black hole and radiation near the event horizon. Because Sgr A* is the nearest such system, the emission characteristics of Sgr A* can be used to study accretion physics in greater detail than is possible in other galaxies. A new opportunity presented itself in 2019 when elevated activity was observed across multiple wavelengths, including the brightest ever flares in the infrared. I used Keck Observatory data to investigate the origin of this unprecedented activity to determine if there was a rain of material from a nearby object (such as the star S0-2 or a gaseous G-object), if Sgr A* underwent a long-term change of state, or if new statistical models are needed. Our results suggest that Sgr A* did experience an episode of enhanced accretion, with material possibly coming from the passage of the gaseous object G2.