Neutron stars are extremely dense stellar corpses which sometimes exist in orbiting pairs known as binary neutron star (BNS) systems. The mass ratio (q) of a BNS system is defined as the mass of the heavier neutron star divided by the mass of the lighter neutron star. Over time the neutron stars will inspiral toward one another and produce a merger event. Although rare, these events can be rich sources of observational data due to their many electromagnetic emissions as well as the gravitational waves they produce. The ability to extract physical information from such observations relies heavily on numerical simulations of merger events. In this project, we report results of six simulations for BNS mergers having total system masses of 2.50 or 2.75Msun and with mass ratios of 1.75, 2.00, and 2.25 (the highest mass ratio simulated in the world). Our goals are to (a) test community-developed models of the ejecta produced by BNS mergers, (b) examine the gravitational waveforms for distinctive spectral characteristics, and (c) estimate the electromagnetic emissions of the merger remnants. Simulations are run using the Einstein Toolkit and employ a semirealistic seven-segment piecewise-polytrope model for the neutron stars based on the Skyrme-Lyon equation of state. We find that the community models of ejecta are robust, with some systematic overestimation of the amount of ejecta produced at extremely high mass ratios. Also, several gravitational wave and electromagnetic characteristics are identified, such as reduced gravitational spectral peaks and extended kilonova emissions in the near infrared for weeks after the merger.
"Binary Neutron Star Mergers: Testing Ejecta Models for High Mass-Ratios,"
The Journal of Purdue Undergraduate Research:
Vol. 10, Article 16.