Dynamical influence of a central massive object on double-barred galaxies: self-destruction mechanism of secondary bars.

The article investigates the dynamical stability of stellar orbits supporting double-barred galaxies—systems featuring a primary large-scale bar and a sub-kiloparsec secondary bar—under the influence of a central massive object (CMO), such as a supermassive black hole or nuclear star cluster. Using test particle simulations within a gravitational potential model that includes a Plummer sphere representation of the CMO, the study reveals that increasing CMO mass induces new orbital resonances that destabilize the secondary bar’s supporting orbits, leading to chaotic motion and eventual destruction of the secondary bar. This destruction typically occurs when the CMO mass reaches approximately 10⁻⁴ to 10⁻³ times the total stellar mass of the galaxy, consistent across varying bar pattern speeds. The findings provide a physical explanation for the co-evolution scenario where the secondary bar drives gas inflow that grows the CMO, which in turn disrupts the secondary bar, halting further CMO growth; this mechanism has implications for understanding the Milky Way’s bulge and the presence or absence of its secondary bar.