Dynamical Tides in White Dwarf Binaries: Theory and Applications

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The end stage of a star like the Sun is a compact star called a white dwarf (WD). A white dwarf no longer produces energy by nuclear fusion, but will glow from residual heat for billions of years. A research team at Cornell University will study WDs that are in a binary system with another astrophysical object. These binary systems can lead to the formation of exotic objects (such as Type Ia supernovae or tidal disruption events), and they are important sources of low-frequency (mHz) gravitational waves (GWs) to be detected by the future Laser Interferometer Space Antenna (LISA). This program will seek to understand the physics of tidal dissipation in the WD, the effect of tidal dissipation on the WD structure and evolution, and how tides affect the GW emission and detection. Visualizations of the results (such as gravity wave breaking and its connection to ocean waves and surfing) will be published on the web for educational purposes. This program will provide support for graduate students, who will receive training in many of the multidisciplinary areas, and in scientific computing. The lead investigator will continue to engage talented undergraduate students in research. The research team will carry out numerical simulations of tidal dissipation via nonlinear internal gravity wave breaking in binary WDs (with the goal of determining the tidal heating profile in the WD), study WD thermal evolution prior to merger, and quantify how tidal effects influence the optical emission and mHz GW signals. The team will also study the long-term evolution of highly eccentric WD-MBH binaries prior to tidal disruption of the WD. They will examine the chaotic growth of WD oscillation modes (“chaotic tides”) due to repeated pericenter passages around the MBH, taking account of the effect of gravitational radiation and WD rotation. The researchers will explore the linear and nonlinear dampings of these modes and study their effects on the WD evolution and mHz GW emission from the WD-MBH binaries. Compact WD binaries are an important source of GW radiation for LISA. The detection of GWs from WD binaries by LISA relies on matched filtering, where a library of template waveforms is matched against instrument data. As such, the accuracy and completeness of the template library is of utmost importance. The scientists will use their tidal binary WD evolution model to compute gravitational waveforms for use in the LISA detection pipeline. This project advances the goals of the NSF Windows on the Universe Big Idea.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.