Dr. Gabriel Perez-Giz is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the Massachusetts Institute of Technology (MIT) Kavli Institute for Astrophysics and Space Research (MKI). The study of orbital motions is core to astronomy and astrophysics. The dynamics of black hole (BH) binaries is especially dynamically rich since the nonlinear footprint of general relativity (GR) will be most visible in the regime of large masses and small separations achievable by such massive compact objects. Unlike in classical celestial mechanics, the motion in such ultra-relativistic binaries is complicated by the loss of energy and angular momentum to gravitational waves (GWs), which causes the orbiting bodies to spiral inward and eventually merge. Unfortunately, systematic numerical study of inspiraling black hole binaries is not possible in the status quo with either numerical relativity (too computationally expensive) or Post-Newtonian approximations (too inaccurate).
However, when the ratio of the masses is extremely small, as when a stellar-mass BH orbits a supermassive galactic BH, the inspiral calculation becomes tractable. The background Kerr spacetime of the larger BH can be regarded as static, the motion of the smaller BH is well approximated as test particle motion in that spacetime, and GW emission and fluxes of conserved quantities can be calculated perturbatively and their back-reaction on the orbit determined. The resulting extreme mass ratio inspiral (EMRI) can be calculated as an adiabatic transit through a sequence of Kerr geodesics. Dr. Scott Hughes at MIT and his collaborators have developed a gold-standard frequency domain code that computes extremely accurate orbits and waveforms for EMRIs of arbitrary initial inclination and eccentricity. Alas, the code still requires ~1.5 CPU-years to generate a single inspiral, making it unsuitable in its present form to study EMRI dynamics systematically.
Dr. Perez-Giz will adapt this code to achieve a many-fold improvement in computational efficiency via a technique exploiting special properties of periodic geodesics around Kerr black holes. An analog to CMBFAST for EMRIs, the resulting GWFaster will make batch calculation of EMRIs on MIT?s Beowulf cluster computationally feasible. Such a tool to compute EMRIs in bulk over large ranges of parameters will allow systematic numerical exploration of myriad unanswered questions in the dynamics of EMRIs, including how initial conditions determine the routes to merger, whether there can be transient resonances between the different orbital frequencies of the infalling object during the inspiral, and how adding spin to the test particle would affect the dynamics. The results will fill a crucial gap in our knowledge of dissipative gravitational dynamics in the only regime in which comparisons to analytic GR solutions are possible.
Dr. Perez-Giz will also conduct a pilot program to help minority and low-income students to access higher education in the physical sciences. Through partnerships with the AT Foundation, a charitable organization that seeks to address the nation's enduring crisis of inequality in education, and Prep for Prep and the Leadership Enterprise for a Diverse America (LEDA), two organizations that advance the educations of minority and low-income students, the proposed educational program will introduce into Prep for Prep and LEDA both advanced research exposure and tiered mentoring for high school and undergraduate students. Both groups already place their low-income and minority participants in top-tier boarding schools and undergraduate institutions in the Boston area but have no formal science-specific research skills training, mentoring or advising in their programs. Giving their student bases the opportunity to develop basic "knife skills" for the physical sciences while they are still in high school and offering guidance during and beyond their undergraduate careers will be a powerful vehicle for addressing the underrepresentation of these same students in the physical sciences.
