Gravitational-Wave Data Analysis and Population Inference

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This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. Gravitational waves, ripples in space-time predicted by Albert Einstein, have been a major boon to the field of astrophysics since they were first directly detected in 2015 by NSF's Laser Interferometric Gravitational-Wave Observatory (LIGO). These gravitational waves travel billions of light years across the universe to Earth and carry clues about how they were originally produced. The violent collisions of black holes and neutron stars have been responsible for the nearly 100 gravitational waves detected so far and provide an excellent testbed for the nature of black holes, nuclear physics, astrophysics of stars, and the expansion of the universe. Under this award, the team at Northwestern University will analyze data collected in the fourth observing run of the advanced interferometer era to characterize gravitational waves and ultimately understand the story of how black holes and neutron stars come into contact with each other in the universe. Their findings will be disseminated to both the astrophysics community as well as the broader public through open-source code bases, eye-catching visualizations, public lectures and hands-on workshops, and a program offering astrophysics research experiences for K-12 teachers.The large number of detections expected in the fourth observing run of the LIGO-Virgo-KAGRA interferometer network will present new computational and organizational challenges for gravitational-wave astrophysicists. At the same time, larger samples of detected gravitational waves will bring to light new questions and in some cases firm answers regarding the formation and evolution of black-hole and neutron-star binaries. The Northwestern University group will develop a concrete framework to analyze the population of binary merger sources, expand abilities for interpretation of the observed population properties, and help plan future observing runs. In parallel, they will identify exceptional gravitational-wave events among the new discoveries and investigate how they may challenge our best understanding and push the frontiers of black-hole and neutron-star astrophysics. Specifically, the team will target a number of problems: the assessment of the significance of event triggers, population inferences from the ensemble of detections, and comparisons with simple models that answer targeted questions about how pairs of black holes and neutron stars come to be and eventually collide with one another.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.