Abstract:
Massive stars end their lives is fiery supernova, leaving behind neutron stars (NSs) and black holes (BHs). These compact remnants of dead stars – the Galactic Underworld –exhibit a fundamentally different distribution and structure to the visible Galaxy. This presentation presents a simulated distribution of NSs and BHs which is significantly less concentrated into a thin disk, with a scale height more than triple that of the visible Galaxy. The differences primarily arise from two effects. Firstly, the distribution of remnants inherits structure from the changing distribution of their parent stars over cosmic time. Secondly, an even larger effect arises from the natal kick received by the remnants during their supernova explosions. We find that almost a third of remnants acquare sufficient kinetic energy to entirely escape the Galaxy, leading to a small Galactic mass loss. The BH–NS fraction increases near the Galactic center: a consequence of smaller kick velocities expected for the former. In the solar neighbourhood, our nearest NS and BH are likely 19 and 21 pc away. Additionally, I'll present some unpublished work predicting how this population can be detected through microlensing events, finding good agreement with independent analysis of Gaia data.