Studying compact object mergers from a new perspective

Understanding the electromagnetic signatures of the mergers of binary compact stellar objects is a critical complement to the nascent field of gravitational wave (GW) astronomy, and this can help scientists understand fundamental issues in modern astrophysics: from how ultra-fast relativistic jets of matter are formed in mergers, to the production of heavy metal elements, from testing gravity and the behavior of matter in extreme conditions to the expansion of the universe as a whole. A project at the University of Maryland, College Park (UMD), will apply new scientific models to a systematic study of GW and related gamma-ray burst afterglows, to derive new constraints on the jet structure and geometry, as well as on the rate of events.

The research activities represent outstanding educational opportunities for students, who will be trained in a number of high-demand astronomy sub-disciplines. The program will also support the UMD GRAD-MAP initiative to lessen the barriers faced by minority students who want to enter astronomy or physics graduate school.

The overarching goal of the project is to provide a coherent physical picture of compact object mergers and their aftermaths. These are complex and highly asymmetric astrophysical systems, and the proposed investigation will provide the foundation for an inclination-aware study of their electromagnetic emission. By using a complementary stream of data from GW and electromagnetic observations (from radio to gamma-rays), the project will map the properties of these mergers across all cosmic times and address the following three main questions: (1) do all compact object mergers produce relativistic jets? (2) what is their role in the production of heavy metals? (3) what is the equation of state (EoS) of matter at extreme densities?

These science objectives will be reached by developing close synergies between observational astrophysics, nuclear physics, gravitational wave astronomy and cosmology. The project involves a combination of existing and new observations of compact object mergers, selected either via gamma-ray burst triggers, gravitational wave alerts, or large-scale optical surveys.

Key features of the method involve: i) the inclusion of complex structures and dfferent geometries (collimated versus isotropic) of the relativistic outflow; ii) the inclusion of a broad range of ejecta morphologies, compositions and velocities; iii) a focus on the effects of viewing angles on the observed emission; iv) novel observational tests to the neutron star EoS. 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.