Rethinking Bar Formation in Disk Galaxies

Stellar bars are ubiquitous in disk galaxies, yet despite decades of theoretical and numerical work, a predictive understanding of when disks become bar unstable remains elusive. Classical approaches based on local stability criteria or idealized global arguments often fail to capture the behavior of realistic disks embedded in external potentials.

In this seminar, I will present results from a suite of high-resolution N-body simulations that point to a new organizing principle for bar formation. Rather than being regulated by local conditions at a specific radius, disks arrange themselves within a global stability landscape defined by their overall dynamical state. Within this framework, disks occupy well-defined regions of stability and instability, naturally explaining why some dynamically cold disks remain stable while others rapidly develop strong bars, and why central mass concentrations play a decisive stabilizing role.

I will then apply this global perspective to the recent discovery of a barred galaxy at z~3 in JWST data, showing how the existence of a bar at such early cosmic times can be naturally understood within this stability landscape. Finally, I will discuss how this criterion is scale-free and extends to disks on much smaller scales, offering a unified view of global m=2 stability from compact disks to galaxies across cosmic time.