WoU-MMA: Collaborative Research: Combining Theory with Observations to Unlock the Multi-Messenger Physics of Compact Binary Mergers

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The detection of gravitational waves (GWs) and electromagnetic (EM) radiation from the binary neutron star (NS) merger GW170817, associated with a short gamma-ray burst (GRB), has heralded the new era of multi-messenger astrophysics. The combined analysis of GWs and light at all wavelengths has enabled us to draw a remarkably detailed picture of a cosmic collision between two NSs, solving the riddle of the origin of heavy elements, confirming the link between compact binary mergers and short GRBs, shedding new light on the physics of relativistic jets, and providing new constraints on cosmology. With only one event so far, however, several key questions remain open. A scientific collaboration between Oregon State University (OSU) and Texas Tech University (TTU) will investigate several major scientific issues through a combination of theoretical and observational research. Astronomers do not yet know whether GW170817 is a typical NS-NS merger, or rather a peculiar transient. The diversity of a larger sample of NS-NS mergers must be studied in order to derive statistically meaningful conclusions about the physics involved. Moreover, a new class of transients arising from mergers of black holes (BHs) with NSs is yet to be studied. Two graduate students and more than six undergraduate students will be trained in research at OSU and TTU. Both of these institutions have student populations dominated by first generation students, and students from local rural communities. The co-principal investigators (PIs) will bring age-appropriate presentations and hands-on activities to the public through partnerships with the Oregon Museum of Science and Industry. TTU will host a prize lecture in the Spanish language, to be delivered by the OSU co-PI. The project has three main goals that will be accomplished by developing and comparing specific event-by-event models, constrained by broad-band data: (i) determining the nature of merger remnants (BH vs NS), as well as the acceleration mechanisms at play in their relativistic outflows, by mapping the diversity of time delays between the GW and EM emissions, and of ejecta angular structures; (ii) shedding light on NS-NS binary evolution models by comparing the properties of the ambient medium around different mergers; (iii) characterizing the variety of merger dynamics and NS properties (magnetization and equation of state) by comparing NS-NS events and NS-BH ones. The OSU group has developed a suite of tools for numerical modelling of EM emission from relativistic jets. The TTU group enjoys access to a variety of already approved observing programs for EM follow-up of GWs. Via this OSU-TTU collaborative project, model predictions will be fed back to the observers in real time, maximizing theoretical understanding while minimizing costs in terms of observational resources. 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.