This award supports research in relativity and relativistic astrophysics and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. The Laser Interferometer Gravitational-Wave Observatory (LIGO) is now repeatedly detecting gravitational waves (GWs)---ripples in space and time---emitted by the collision of compact objects millions, sometimes billions, of light-years from Earth. Most of these objects have been black holes, others have been neutron stars. From the GWs, scientists can measure properties (locations, masses, spins) of the objects and learn about how they might have formed and how they warp space and time as they collide; for neutron stars, the collision also produces gamma-rays and other electromagnetic radiation, and together with the GWs this teaches scientists how matter behaves at ultra-high densities and how some chemical elements were formed. But these studies require comparing the detected GWs with detailed predictions of the waves. The predictions are made using the equations of General Relativity, written down by Einstein in 1915 but unsolvable (for colliding compact objects) until about 2005 with the development of advanced methods and powerful supercomputers. This project supports theoretical work designed to underpin and improve LIGO's ability to extract from observed GWs the rich information that the waves carry, and to improve the interpretation of LIGO events with electromagnetic counterparts. This includes the improvement and use of the Spectral Einstein Code (SpEC), currently the most accurate computer code for solving Einstein's equations for black hole binaries. SpEC will be used to carry out numerical solutions of black-hole collisions for the purpose of analyzing LIGO data. In addition, a next-generation computer code SpECTRE, under development, will be used to predict GWs from two colliding neutron stars and from a black hole colliding with a neutron star, and will be used to study accretion disks that form after the merger. This program will also serve as a training ground for young physicists and astrophysicists. The new code SpECTRE and its output will be publicly released. The group members will reach out to the general public through lectures, interactive web pages, and YouTube videos.
By combining analytical techniques and numerical simulations with the Spectral Einstein Code (SpEC): (i) GW signals for BBHs will be generated for use in LIGO data analysis in poorly-explored regions of the BBH parameter space, and will be used to produce numerical surrogate models that can evaluate a single waveform in milliseconds while retaining the accuracy of full numerical simulations; and (ii) the dynamical behavior of highly curved spacetime will be explored via analytic, perturbative, and numerical approaches, which will include studies of quasinormal mode excitations, exotic compact objects, beyond-Einstein theories of gravitation, and extreme mass ratio inspirals. A combination of analytic techniques and the next-generation open-source code SpECTRE will be applied to studies of BHNS and NSNS binaries and accretion disks to understand multi-messenger events. This will include investigations of post-merger accretion disks and tidal coupling. Parameter estimation will be investigated for signals that might be detected by both ground-based and space-based detectors, and the science case for possible future deci-Hertz gravitational-wave detectors will be explored.
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.
