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The problem of how some disk galaxies avoid forming bars remains unsolved.Many galaxy models having reasonable properties continue to manifest vigorousinstabilities that rapidly form strong bars and no widely-accepted idea has yetbeen advanced to account for how some disk galaxies manage to avoid thisinstability. It is encouraging that not all galaxies formed in recentcosmological simulations possess bars, but the dynamical explanation for thisresult is unclear. The unstable mode that creates a bar is understood as astanding wave in a cavity that reflects off the disk center and the corotationradius, with amplification at corotation. Here we use simulations to addressone further idea that may perhaps inhibit the feedback loop and thereforecontribute to stability, which is to make the disk center dynamically hotand/or to taper away mass from the inner disk, which could be masked by abulge. Unfortunately, we find that neither strategy makes much difference tothe global stability of the disk in the models we have tried. While deepdensity cutouts do indeed prevent feedback through the center, they stillreflect incoming waves and thereby provoke a slightly different instabilitythat again leads to a strong bar.

The stability of some galaxy disks is still perplexing