# Bar formation in the Milky Way type galaxies

## TL;DR

This paper demonstrates that bar formation in cuspy Milky Way-like galaxies is possible when disc thickness is considered, resolving previous discrepancies and suggesting recent formation of such bars.

## Contribution

It shows that including disc thickness in models explains bar formation in cuspy galaxies, challenging prior beliefs about the impossibility of such instabilities.

## Key findings

- Bar formation is possible in cuspy galaxies with thick discs.
- Growth time of bars is about 250 Myr for typical disc masses.
- Rigid halo/bulge potentials increase the growth time significantly.

## Abstract

Many barred galaxies, possibly including the Milky Way, have cusps in the centres. There is a widespread belief, however, that usual bar instability taking place in bulgeless galaxy models is impossible for the cuspy models, because of the presence of the inner Lindblad resonance for any pattern speed. At the same time there are numerical evidences that the bar instability can form a bar. We analyse this discrepancy, by accurate and diverse N-body simulations and using the calculation of normal modes. We show that bar formation in cuspy galaxies can be explained by taking into account the disc thickness. The exponential growth time is moderate for typical current disc masses (about 250 Myr), but considerably increases (factor 2 or more) upon substitution of the live halo and bulge with a rigid halo/bulge potential; meanwhile pattern speeds remain almost the same. Normal mode analysis with different disc mass favours a young bar hypothesis, according to which the bar instability saturated only recently.