Unfolding the Dynamic and Colorful Lives of Compact Object Mergers

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The mergers of two astronomical compact objects (neutron stars and/or black holes) in a binary system serve as sources of gravitational wave emission, potential sites of heavy element nucleosynthesis, and laboratories for high-energy astrophysical processes not seen elsewhere in the universe. With the onset of advanced gravitational wave detectors, only recently have astronomers begun to place direct constraints on these processes. Short gamma-ray bursts (SGRBs), which are detected at cosmological distances, also offer a unique and independent window into the dynamic and colorful lives of compact object mergers. A research group at Northwestern University, under the direction of the principal investigator (PI), will capitalize on complementary streams of data from gravitational wave observatories, ground-based telescopes and space-based gamma-ray and X-ray missions to: (i) develop informed follow-up strategies for electromagnetic (EM) observations following gravitational wave events, (ii) confront theoretical models of heavy element production in mergers with optical and near-infrared observations, (iii) place constraints on the fraction of mergers that produce SGRBs with radio through X-ray observations, and (iv) decipher the histories of the pre-merger binary systems with a complete census of their host galaxies. To make this research publicly accessible in a novel way, the PI will partner with Evanston (Illinois) Township High School (ETHS) which has an on-campus planetarium. The PI will use the planetarium as a venue for engaging students with research material and exposing students to Astronomy researchers from diverse backgrounds.The research group will utilize the inferred properties of previous SGRBs to build light curve prediction tools that will optimize an observatory's chance of an EM counterpart detection following a gravitational wave event. These adaptable tools will serve as an important community resource, not only for determining current observing strategies but also for planning future EM surveys. The research group will also place direct, observational constraints on the role of mergers in populating the Universe with heavy elements, by determining independently-measured ejecta masses and event rates. The researchers will build a complete census of SGRB host galaxies and the spatial offsets of bursts from the galaxy centers. From these observations, the researchers will determine the distributions of merger kick velocities and delay times. These distributions are vital inputs for binary evolution models, yet they are highly uncertain. The project is well-designed to exploit both methods of merger discovery: gravitational wave emission from Advanced LIGO/Virgo and gamma-ray burst detection from space-based missions. For all objectives in this proposal, the research group will make crucial connections between the local population of compact object mergers discovered by Advanced LIGO/Virgo and their cosmological analogues.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.