Nonlinear Hydrodynamics in Gravitational-Wave, High-Energy, and Exoplanetary Astrophysics
by
Online
Tsung-Dao Lee Institute
Host: Dong Lai
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Abstract:
Nonlinear hydrodynamics plays a central role in shaping the evolution of compact binaries across astrophysics. In this talk, I will discuss nonlinear effects in two classes of systems. The first is coalescing neutron star (NS) binaries. I will show that nonlinear interactions primarily manifest as shifts in the natural frequencies of NS oscillation modes, in particular, the fundamental and gravity modes. As a result, nonlinearities can substantially enhance the dynamical tidal response of NSs and produce gravitational-wave phase shifts of order one radian. Modeling this effect provides a new probe of NS physics beyond the linear tidal deformability, while neglecting it can bias the equation-of-state inference, especially when information from a population of detections is combined. The same theoretical framework also enables a first-principles description of post-merger oscillations in merger remnants. In the second half of the talk, I will discuss how nonlinear hydrodynamics determines the Roche limit in eccentric, asynchronous binaries. This theoretical breakthrough explains results from previous numerical simulations and enables their reliable extrapolation. As an application, I will present a new model of repeated partial tidal disruption events (rpTDEs) that naturally produces the irregular recurrence times that have been observed in at least some candidates.
Biography:
Hang Yu is a theoretical astrophysicist and Assistant Professor of Physics at Montana State University (2023-). He received his Ph.D. in Physics from MIT in 2019, followed by postdoctoral fellowships at Caltech (2019-2022) and the Kavli Institute for Theoretical Physics (2022-2023). His research focuses on nonlinear hydrodynamics and tidal interactions in compact binaries, with applications to gravitational-wave sources, high-energy transients, and exoplanetary systems.
