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A universal route for the formation of massive star clusters in giant molecular clouds


Young massive clusters (M ≥ 104Mʘ) are proposed modern-day analogues of the globular clusters that were products of extreme star formation in the early Universe1,2,3,4. The exact conditions and mechanisms under which young massive clusters form remain unknown4,5—a fact further complicated by the extreme radiation fields produced by their numerous young stars6,7,8,9. Here, we show that massive clusters are naturally produced in radiation-hydrodynamic simulations of isolated 107Mʘ giant molecular clouds with properties typical of the local Universe, even under the influence of radiative feedback. In all cases, these massive clusters grow to globular cluster masses within 5 million years (Myr) via a roughly equal combination of filamentary gas accretion and mergers with less massive clusters. Lowering the heavy-element abundance of the molecular cloud by a factor of ten reduces the opacity of the gas and better represents the high-redshift Universe10,11. This results in higher gas accretion, leading to a mass increase of the largest cluster by a factor of around four. When combined with simulations of less massive molecular clouds12 (104–6Mʘ), a clear relation emerges between the maximum cluster mass and the mass of the host cloud13. Our results indicate that young massive clusters—and potentially globular clusters—are simple power-law extensions of local cluster formation, and are insensitive to star formation thresholds. A universal picture emerges without the need for exotic formation scenarios1315.

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Fig. 1: Formation of the most massive star cluster and its merging partners.
Fig. 2: Accretion-merger histories of the YMCs.
Fig. 3: Gaseous flow rate in the vicinity of the YMCs.
Fig. 4: Maximum cluster mass produced by a given GMC mass.


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This research was financially supported by the Natural Sciences and Engineering Research Council through a postgraduate scholarship and Discovery Grants. Computations were performed on the GPC supercomputer at the SciNet HPC Consortium. SciNet is funded by the Canada Foundation for Innovation under the auspices of Compute Canada; Government of Ontario; the Ontario Research Fund: Research Excellence; and the University of Toronto.

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Authors and Affiliations



C.S.H. carried out the simulations and completed the data analysis and figure production. All authors contributed to the interpretation of the results and were involved in writing the final manuscript.

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Correspondence to Corey S. Howard.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Figures 1–5, Supplementary Video captions 1–6, Supplementary discussion

Supplementary Video 1

Full cloud visualization of the column density and cluster movement for the solar metallicity (Zʘ) simulation

Supplementary Video 2

Zoomin of the central 35 pc region showing only the clusters that merge to the young massive cluster (1 Zʘ simulation)

Supplementary Video 3

Full cloud visualization of the column density and cluster movement for the 0.1 Zʘ simulation

Supplementary Video 4

Zoom-in of the central 35 pc region showing only the clusters that merge to the young massive cluster (0.1 Zʘ simulation)

Supplementary Video 5

The density and gas flow rate of a 5 pc spherical region centered on the 1 Zʘ young massive cluster

Supplementary Video 6

The density and gas flow rate of a 5 pc spherical region centered on the 0.1 Zʘ young massive cluster

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Howard, C.S., Pudritz, R.E. & Harris, W.E. A universal route for the formation of massive star clusters in giant molecular clouds. Nat Astron 2, 725–730 (2018).

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