An upper limit to the masses of stars


There is no accepted upper mass limit for stars. Such a basic quantity eludes both theory and observation, because of an imperfect understanding of the star-formation process and because of incompleteness in surveying the Galaxy1. The Arches cluster2,3,4,5,6,7 is ideal for investigating such limits, being large enough to expect stars at least as massive as 500 solar masses ( 500 M; based on a typical mass function), and young enough for its most massive members to still be visible. It is also old enough to be free of its natal molecular cloud, it is at a well-established distance, and it is close enough for us to discern its individual stars2. Here I report an absence of stars with initial masses greater than 130 M in the Arches cluster, whereas the typical mass function predicts 18. I conclude that this indicates a firm limit of 150 M for stars; the probability that the observations are consistent with there being no upper limit is 10-8.

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Figure 1: Observed frequency distribution and inferred masses of stars in the Arches cluster versus brightness.
Figure 2: Frequency distribution versus mass for stars in the Arches cluster extracted from data in Fig. 1.


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I acknowledge discussions with P. Najarro, R. Larson, N. Walborn, J. Puls, N. Panagia, M. Morris, C. Weidner, P. Kroupa, R. M. Rich, V. Bromm and M. Livio.

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Correspondence to Donald F. Figer.

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Supplementary information

Supplementary Figures 1-4 and Legends

Supplementary Figure 1: The Arches cluster, as imaged in infrared light with the Hubble Space Telescope Near-Infrared Camera and Multi-object Spectrometer. Supplementary Figure 2: Luminosity versus temperature for massive stars. Supplementary Figure 3: Present versus initial mass for massive stars at a variety of ages. Supplementary Figure 4: Results of Monte-Carlo simulation. (DOC 745 kb)

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Figer, D. An upper limit to the masses of stars. Nature 434, 192–194 (2005).

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