Neutron Stars & Black Holes: Astrophysical Laboratories for Nuclear Physics and Nuclear Yardsticks for Astrophysical Phenomena

Reed Essick (University of Toronto) — May 29, 2025

Abstract

The physics of compact objects, such as Neutron Stars and Black Holes, remains at the forefront of astronomical theory and experiment. In particular, there is significant uncertainty in the nuclear physics that governs the cores of Neutron Stars and sculpts the entire population of stellar remnants. I will discuss how to use theoretical insights about the behaviour of these exotic objects, together with cutting-edge inference techniques, to improve constraints from multi-messenger observations. Similarly, I will show a few examples of how improved theoretical understanding of compact object properties can inform our understanding of a broad range of astrophysical phenomena. I will discuss the current state of the field, with a focus on insights enabled by the technology I’ve developed, what we are likely to learn over the coming years, and promising paths towards deep physical insights about the behaviour of supranuclear matter and dynamic, strong-field gravity.

Beyond the first wave: understanding binary neutron star and black hole formation channels

Lieke Van Son (Harvard University) — November 25, 2024

Abstract

After the first waves of gravitational-wave detections, it often seems as though we are left with more questions than answers. The hope of finding “one formation channel to rule them all” has given way to “one channel for every system.” This shift is not necessarily a drawback: moving away from a single unifying framework allows us to focus on specific properties—such as mass ranges—and connect observed features to their progenitors.

In this talk, I will focus on lower-mass compact objects and discuss key findings on which recent studies are converging, such as: why binary neutron stars are expected to form through only a single channel, and why binary black hole formation is metallicity dependent, while binary neutron star formation is not (or much less so). I will explore the “if” and “why” behind each of these findings, their broader implications for merger predictions and cosmology, and how we can test them with upcoming gravitational-wave and electromagnetic observations.

Given the increasing sensitivity of existing gravitational wave detectors, we expect gravitational waves from neutron star mergers to be observed in the coming years. In order to extract as much information as possible from these observations, reliable models of the gravitational wave and electromagnetic signals powered by mergers are necessary. In this talk, I will discuss our efforts to study binary mergers using general relativistic simulations. I will in particular focus on recently developed gravitational wave models which account for tidal effects in neutron stars, on the electromagnetic transients powered by radioactive decays in the matter ejected by neutron star mergers, and on the outcome of nucleosynthesis in that ejecta. Tidal effects in neutron star mergers can provide us with information about the size of neutron stars, an important observable in nuclear physics, while radioactively powered transients can offer both improved localization of the merger events and additional information about the properties of the merging objects.

Details

Francois Foucart

Lawrence Berkeley National Lab

December 8, 2016