NSF-BSF: Getting to the Core of Core Formation and Core Dynamics

The central regions of galaxies are extremely diverse; while some galaxies have extremely dense 'cusps' of stars and dark matter, others have extended low-density cores. This suggests that there are multiple pathways to the formation of galactic nuclei. A team of experts from the US (NSF-funded) and Israel (BSF-funded) will undertake a comprehensive study of both core formation and core dynamics. They will make reliable estimates of the merger rate of super-massive black holes (SMBHs) detectable with the Laser Interferometer Space Antenna and for the off-centering fractions of SMBHs and nuclear star clusters in dwarf galaxies. Complementing this research program, this team will contribute to K-12 science education and outreach, addressing the critical need for students to engage in STEM-related disciplines. They will promote careers and interest in STEM through Yale’s Pathway to Science Summer Scholars program by developing and running summer programs in astronomy. While the Cold Dark Matter (CDM) paradigm predicts that dark matter halos have dense central cusps, some galaxies have central constant-density cores. The presence of such cores either hints at an alternative to CDM, such as self-interacting dark matter (SIDM), or requires intriguing dynamical processes involving baryons or supermassive black holes (SMBHs). Cores are also intriguing because they manifest unexpected dynamics. In particular, simulations have shown that dynamical friction does not operate inside cores, causing ‘core-stalling’, and that massive objects within a core experience a ‘dynamical buoyancy’ that pushes them outward. These processes can prevent massive objects such as nuclear star clusters and/or SMBHs from reaching, or remaining, at the center of their potential well, which can have important implications. The investigators will (i) further develop the novel model CuspCore and test it against numerical simulations, opening up a new avenue to analytically model the response of multi-component, gravitational systems to a wide variety of perturbations without having to resort to CPU-intensive simulations, and (ii) establish the necessary conditions for core stalling and buoyancy to operate in both CDM and SIDM halos. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.