One of the longstanding questions in galaxy dynamics is what determines whether a rotating stellar disk remains stable or forms a bar. While local stability criteria—like the Toomre Q parameter—have provided valuable insights, a general global criterion for bar formation has remained elusive. In this talk, I will present results from a new suite of high-resolution N-body simulations designed to test the global stability of stellar disks to the m = 2 bar mode. Crucially, our models do not assume that the disk is isolated and purely self-gravitating. Instead, the disk evolves within an external gravitational field, reflecting more realistic galactic environments. Our analysis identifies two key global, dimensionless parameters that appear to govern the onset of bar instability. These two parameters define a "stability plane" that separates bar-stable from bar-unstable systems. Unlike local criteria, this new framework provides a physically motivated, global condition for bar formation that can be applied across a wide range of galactic environments—including gas-rich, turbulent disks at high redshift. I’ll discuss the implications of this result for understanding the emergence of bars across cosmic time and in galaxies like our own Milky Way.
Speaker: Elena D'Onghia, Associate Professor, University of Wisconsin, Madison
Host: Tjitske Starkenburg
CIERA Astrophysics
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