Mergers of binary systems involving neutron stars and/or black holes are the main source of gravitational waves for ground-based interferometers like LIGO, Vigo, and KAGRA. While the precision in sky localization from gravitational waves alone is limited, the simultaneous detection of electromagnetic counterparts significantly reduces uncertainties and provides complementary information about these events. This synergy was demonstrated by the multi-messenger detection of the neutron star merger GW170817.
One of the most easily detectable electromagnetic counterparts is the transient known as a kilonova. Kilonovae arise from mass ejected during the merger, and are powered by the radioactive decay of newly-formed heavy (r-process) elements like gold or lead.
Mass ejection during the merger can occur through various processes that operate on the dynamical (orbital), thermal, or accretion (viscous or secular) timescales. Our research primarily focuses on characterizing mass ejection from the accretion disk around the merger remnant, which occurs over thousands of orbital times. To achieve this, we employ multi-dimensional magneto-hydrodynamic simulations that incorporate neutrino radiation transport and nuclear physics.
Stellar-mass black holes are born following the core-collapse of a massive star, either when the supernova explosion fails or when matter collapses back to the center in an under-energetic explosion. The groundbreaking detection of numerous binary black hole events by the LIGO/Virgo gravitational wave observatories has revolutionized our understanding of the universe's black hole population and motivates further scientific inquiries. These include investigating the ratio of successful to failed supernovae, elucidating the internal rotation of presupernova stars, and exploring other factors such as the onset of pair instability in massive stars.
Our research focuses on characterizing the observational signatures of black hole formation in failed supernovae. We investigate diverse aspects, ranging from mass ejection in non-rotating failed supernovae to outflows from accretion disks in collapsars, where significant progenitor rotation is present. Our models generate predictions for the electromagnetic signal emitted during these events, directly impacting transient surveys. Additionally, our research provides quantitative estimates of heavy element yields, contributing to nucleosynthesis studies.