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When galactic discs settle and become massive enough, they are able to formstellar bars. These non-axisymmetric structures induce shocks in the gas,causing it to flow to the centre where nuclear structures, such as nucleardiscs and rings, are formed. Previous theoretical and observational studieshave hinted at the co-evolution of bars and nuclear discs, suggesting thatnuclear discs grow "inside-out", thereby proposing that smaller discs live inyounger bars. Nevertheless, it remains unclear how the bar and the nuclearstructures form and evolve with time. The smallest nuclear discs discovered todate tend to be larger than $\sim200~\rm{pc}$, even though some theoreticalstudies find that when nuclear discs form they can be much smaller. Using MUSEarchival data, we report for the first time two extragalactic nuclear discswith radius sizes below $100~\rm{pc}$. Additionally, our estimations reveal theyoungest bars found to date. We estimate that the bars in these galaxies formed$4.50^{+1.60}_{-1.10}\rm{(sys)}^{+1.00}_{-0.75}\rm{(stat)}$ and$0.7^{+2.60}\rm{(sys)}^{+0.05}_{-0.05}\rm{(stat)}~\rm{Gyr}$ ago, for NGC\,289and NGC\,1566, respectively. This suggests that at least some disc galaxies inthe Local Universe may still be dynamically settling. By adding these resultsto previous findings in the literature, we retrieve a stronger correlationbetween nuclear disc size and bar length and we derive a tentative exponentialgrowth scenario for nuclear discs.

Disc galaxies are still settling: The discovery of the smallest nuclear discs and their young stellar bars