Neutron Star Mergers
A small fraction of all neutron stars (NS) end their life with a violent collision with another compact object, another NS or a Black Hole (BH). These collisions can be driven by the loss of orbital energy due to the emission of gravitational waves at the end of a complex binary evolution, or they can occur as a result of many-body interactions in dense stellar environments (for example, in globular clusters). Presently, about a dozen double NS systems in and around our galaxy are known. Of these, roughly half will merge within a few billions of years. There are currently no known NS-BH binaries.
The estimated event rates based on these observations and other means are still very uncertain. For double NS binaries, the merger rate estimates range from one every thousand years to one every million years for a galaxy lik ours. The rates for NS-BH binaries are even more uncertain, with one predicted every 10,000 to 100 million years per Milky-Way-type galaxy.
A volume rendering of the density after the merger of a 0.6 and 0.9 solar mass white dwarf. This image is from a calculation that was performed on ORNL's Titan supercomputer. The infrastructure for modeling white dwarf mergers is included with Castro.
- White Dwarf Mergers on Adaptive Meshes. I. Methodology and Code Verification, M. P. Katz, M. Zingale, A. C. Calder, F. D. Swesty, A. S. Almgren, & W. Zhang, 2016, ApJ, 819, 94