Collaborative Research: WoU-MMA Constraining the nuclear equation of state and population of neutron star mergers through observations of transient and persistent phenomena

Neutron stars (NSs) are formed when a massive star reaches the end of its life: the outer layers of the star are ejected in a violent explosion but the core of the star collapses to form a small, dense remnant. NSs that form a binary system with another NS sometimes in-spiral and merge, producing gravitational waves and a bright transient that is thousands of times more luminous than a nova (a so-called kilonova). NS-NS mergers have been detected by the NSF-funded Laser Interferometer Gravitational wave Observatory (LIGO). A team from the Rochester Institute of Technology and the University of Tennessee Knoxville will continue their program to use advanced computational models to better understand NS-NS mergers and NS physics. They will produce realistic models of the kilonova explosion, improve estimates of the neutron mass distribution, and better understand neutron star populations. The models will be benchmarked against gravitational wave and electromagnetic detections of NS-NS mergers. The program includes training and mentoring of graduate students and postdoctoral researchers; participation in a Rochester Institute of Technology program (ROAR) that introduces high school students from underrepresented minorities to research; and development of a new undergraduate course at the University of Tennessee Knoxville focused on gravitational waves. The detailed science goals of the proposal are; extend ongoing work to produce more systematic kilonova models, calibrated to simulations and exploring relevant systematic uncertainties; incorporate rapid r-process observations systematically into joint inference about NS population properties and the equation of state (EOS), allowing for alternatives, to assess the origin of r-process elements; use the tools developed as part of this program to reconstruct the population of NS, the nuclear EOS, and the origin of r-process elements; and assess the ability of the tools to draw these inferences. The proposed research involves producing realistic models of the kilonova explosion that occurs when neutron stars collide and merge. These models will be benchmarked against gravitational wave and electromagnetic detections of NS-NS mergers, thereby improving estimates of the neutron mass distribution and better understanding neutron star populations. Thus, this project is aligned with the science mission of the Windows on the Universe: Multi-Messenger Astronomy (WoU-MMA) 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.