Gravity seminar - Ivan Markin Seminar

Event details

Title: Black hole-neutron star mergers with equal and near-equal mass ratios

Abstract: The gravitational-wave (GW) event GW230529 confirmed the existence of black hole-neutron star (BHNS) mergers with component masses more similar than was generally expected, with the black hole being only around 2.5 times more massive than the neutron star. In contrast to more asymmetric BHNS systems, such near-equal-mass and equal-mass BHNS mergers produce massive remnant disks responsible for bright electromagnetic (EM) transients like kilonovae and gamma-ray bursts. Observations of gravitational waves and the EM counterparts of these systems can help us understand the formation channels of BHNS systems and constrain the properties of nuclear matter at the most extreme densities found in neutron stars. However, numerical-relativity simulations of these systems are scarce, and the parameter space remains sparsely populated. Simulations with long inspiral stages are required to calibrate gravitational wave models, which is crucial for accurate and unbiased interpretation of GW events. Moreover, the postmerger properties of disks and ejecta are crucial for interpreting the EM emission and are yet to be systematically mapped. In this seminar, I will discuss the astrophysics of equal- and near-equal-mass BHNS, the numerical challenges and insights from their recent simulations, and the new questions they raise.