In the centres of the Milky Way and M83, the global environmental properties thought to control star formation are very similar. However, M83’s nuclear star formation rate (SFR), as estimated by synchrotron and H α emission, is an order of magnitude higher than the Milky Way’s. To understand the origin of this difference we use ALMA observations of HCN (1 − 0) and HCO+ (1 − 0) to trace the dense gas at the size scale of individual molecular clouds (0.54 arcsec, 12 pc) in the inner ∼500 pc of M83, and compare this to gas clouds at similar resolution and galactocentric radius in the Milky Way. We find that both the overall gas distribution and the properties of individual clouds are very similar in the two galaxies, and that a common mechanism may be responsible for instigating star formation in both circumnuclear rings. Given the considerable similarity in gas properties, the most likely explanation for the order of magnitude difference in SFR is time variability, with the Central Molecular Zone (CMZ) currently being at a more quiescent phase of its star formation cycle. We show M83’s SFR must have been an order of magnitude higher 5–7 Myr ago. M83’s ‘starburst’ phase was highly localized, both spatially and temporally, greatly increasing the feedback efficiency and ability to drive galactic-scale outflows. This highly dynamic nature of star formation and feedback cycles in galaxy centres means (i) modelling and interpreting observations must avoid averaging over large spatial areas or time-scales, and (ii) understanding the multiscale processes controlling these cycles requires comparing snapshots of a statistical sample of galaxies in different evolutionary stages.

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M83的中心和银河系：共同恒星形成周期的相反极端

在银河系和 M83 的中心，被认为控制恒星形成的全球环境特性非常相似。然而，根据同步加速器和 H α 发射估计，M83 的核恒星形成率 (SFR) 比银河系高一个数量级。为了了解这种差异的起源，我们使用 ALMA 对 HCN (1 - 0) 和 HCO+ (1 - 0) 的观测来追踪内部 ∼500 pc 的 M83，并将其与银河系中类似分辨率和半心半径的气体云进行比较。我们发现，两个星系中的整体气体分布和单个云的性质都非常相似，并且一个共同的机制可能是导致两个环核环中恒星形成的原因。鉴于气体性质相当相似，恒星形成率数量级差异的最可能解释是时间变异性，中央分子区（CMZ）目前处于其恒星形成周期的更静止阶段。我们展示了 M83 的恒星形成率在 5-7 Myr 之前一定要高一个数量级。M83 的“星暴”阶段在空间和时间上都高度局部化，大大提高了反馈效率和驱动银河尺度外流的能力。星系中心恒星形成和反馈周期的这种高度动态特性意味着（i）建模和解释观测必须避免在大空间区域或时间尺度上进行平均，