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tokens: physical motion of a single massive star-forming region. 3.1. Two Morphological Classes of FIRE-CMZs The FIRE galaxies presented here cover a range of morphologies in their centers because these simulations were not designed to match the detailed structural properties of our Galactic center. Within the sample of seven galaxies, we see two distinct classes of central morphology in their fiery cores (gas and star formation distributions within R ≈ 1.5 kpc): (a) “Asymmetric/Bursty” (m12b, m12c, m12f, and m12w): Large, asymmetric gas clouds and star-forming complexes are seen. Star formation is concentrated in intense starbursts whose feedback dramatically shapes the local gas environment (see m12b, upper subfigure of Figure 1 ). Two simulations falling in this category (m12b and m12f) simultaneously match the MW CMZ gas and SFR measurements. The two others (m12c and m12w) do not simultaneously have SFR and dense gas tracers within the central 145 pc at any point in this time window. (b) “Smooth” (m12i, m12m, and m12r): Gas and star formation is smoothly distributed within the galactic centers, with clear feeding of gas into center, and a cirrus of star formation (see m12m, lower subfigure of Figure 1 ). Feedback events do not dramatically alter the local gas environment, as the feedback is relatively dispersed across their centers. Interestingly, none of the galaxies here exhibit the ring structures, presumed to be long-lived, seen by studies of the central regions of other spiral galaxies and the MW CMZ (Kormendy Kennicutt 2004 ; Molinari et al. 2011 ). We note the lack of strong bars in the centers of any of these FIRE galaxies at this time (m12m did develop a strong bar around z ≈ 0.2, but it does not survive to z = 0; Debattista et al. 2019 ); without the presence of bars in these simulations at z = 0, we cannot speak to the dynamical importance of bars in producing central galactic environments similar to the MW CMZ. Other work has highlighted the potential impacts of bars in funneling gas core-ward and forming rings (Sormani et al. 2015 , 2018 ). However, bar-induced effects would likely push these simulated galactic centers toward more asymmetric states, supporting the idea that bursty, rather than steady-state, star formation is necessary to explain MW CMZ observations. Specifically, Sormani et al. ( 2018 ) showed that the gas flow in a barred potential naturally becomes turbulent and asymmetric, even in the absence of any type of stellar feedback. And so, we leave it to future work to investigate the gas flows driven in FIRE galaxies by the bars that form at higher redshift. The structures in the centers of the FIRE galaxies appear to be fairly transient in nature, existing for ≲10 Myr (similar to the GMC lifetimes seen in these simulations more broadly by Benincasa et al. 2020 ). We should be clear: spiral structures do exist core-ward in these simulations (see the clear presence of spiral arms in both m12b and m12m in Figure 1 ). In