The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M⊙ stellar mass limit

By P. Crowther, O. Schnurr, R. Hirschi, N. Yusof, R. Parker, S. Goodwin, H. A. Kassim. 2010

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Spectroscopic analyses of hydrogen-rich WN5‐6 stars within the young star clusters NGC 3603 and R136 are presented, using archival Hubble Space Telescope and Very Large Telescope spectroscopy, and high spatial resolution near-IR photometry, including MultiConjugate Adaptive Optics Demonstrator (MAD) imaging of R136. We derive high stellar temperatures for the WN stars in NGC 3603 (T∗ ∼ 42±2 kK) and R136 (T∗ ∼ 53± 3 kK) plus clumping-corrected mass-loss rates of 2 ‐ 5 ×10 −5 M⊙ yr −1 which closely agree with theoretical predictions from Vink et al. These stars make a disproportionate contribution to the global ionizing and mechanical wind power budget of their host clusters. Indeed, R136a1 alone supplies ∼7% of the ionizing flux of the entire 30 Doradus region. Compar isons with stellar models calculated for the main-sequence evolution of 85 ‐ 500 M⊙ accounting for rotation suggest ages of ∼1.5 Myr and initial masses in the range 105 ‐ 170 M⊙ for three systems in NGC 3603, plus 165 ‐ 320 M⊙ for four stars in R136. Our high stellar masses are supported by consistent spectroscopic and dynamical mass determinations for the components of NGC 3603 A1. We consider the predicted X-ray luminosity of the R136 stars if they were close, colliding wind binaries. R136c is consistent with a colliding wind binary system. However, short period, colliding wind systems are excluded for R136a WN stars if mass ratios are of order unity. Widely separated systems would have been expected to harden owing to early dynamical encounters with other massive stars within such a high density environment. From simulated star clusters, whose constituents are randomly sampled from the Kroupa initial mass function, both NGC 3603 and R136 are consistent with an tentative upper mass limit of ∼300 M⊙. The Arches cluster is either too old to be used to diagnose the upper mass limit, exhibits a deficiency of very massive stars, or mo re likely stellar masses have been underestimated ‐ initial masses for the most luminous stars in the Arches cluster approach 200 M⊙ according to contemporary stellar and photometric results. The potential for stars greatly exceeding 150 M⊙ within metal-poor galaxies suggests that such pair-instab ility supernovae could occur within the local universe, as has been claimed for SN 2007bi.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/0438620bdd9fe0adb1d8ca51ecedfa5a9842b48e

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Citations in the corpus

• The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class (2014, methodology): “While the highest initial mass for which tracks are given by Meynet & Maeder (2005) is 120 M , the most luminous star of this group (BAT99 108), if indeed a single star, requires about 300 M , as already pointed out by Crowther et al. (2010).”
• The stellar and sub-stellar IMF of simple and composite populations (2011, methodology): “The star-burst cluster R136 is associated with super-canonical stars (Crowther et al. 2010) and is therefore a super-saturated population.”
• Ultraluminous X-ray sources in the Chandra and XMM-Newton era (2011, background): “This is not becauseof the lack of very massive stars (in fact, several stars with ini ial masses∼ 150–300M⊙ may exist in the LMC; Crowther et al. 2010), but because Helium cores more massive than≈ 70M⊙ (corresponding to initial stellar masses& 140M⊙ at zero metallicities) undergo an…”
• The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of He II λ1640 in young star clusters (2016, methodology): “Star T∗ log L XH Code Minit vinit Mcurrent τ (kK) (L ) ( per cent) (M ) (km s−1) (M ) (Myr) R136a1 53 ± 3 6.94 ± 0.09 – Bonn 325+55−45 100+180−60 315+60−50 0.0+0.3−0.0 53 ± 3 6.94 ± 0.09 40 ± 10 Bonn 315+50−20 440+20−85 280+35−30 0.8 ± 0.2 53 ± 3 6.94 ± 0.09 40 ± 5 Geneva 320+100−40 400 265+80−35 1.”
• Fluctuating feedback-regulated escape fraction of ionizing radiation in low-mass, high-redshift galaxies (2017, background): “At these scales, the IMF cannot be fully sampled: Crowther et al. (2010) found, for instance, several stars with masses above 150 M in the R136 star cluster in the Milky Way.”
• Core-collapse explosions of Wolf–Rayet stars and the connection to Type IIb/Ib/Ic supernovae (2011, background): “…most W-R stars are inferred to stem from stars with a main-sequence mass in excess of 25 M⊙, potentially extending to huge masses of a few 100 M⊙ (Crowther et al. 2010), generically characterised by a large luminosity of 105–106 L⊙ and large mass-loss rates of∼10−5M⊙ yr−1 (Crowther 2007).”
• The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “There may also be an upper cutoff somewhere between 100 and 150 M (Elmegreen 2000; Weidner & Kroupa 2004; Figer 2005), although this possibility has been challenged by recent observations of stars that appear to exceed the proposed limit (Crowther et al. 2010; Doran et al. 2013).”
• The Observer's Guide to the Gamma-Ray Burst-Supernova Connection (2016, background): “[409, 410]) which contains many of the most massive and luminous stars known, including R136a1 (M∼ 315 M , L∼ 8.”
• Dawes Review 6: The Impact of Companions on Stellar Evolution (2016, background): “The most massive stars, such as the ∼320 M R136a1 (Crowther et al., 2010), are also quite likely to be binary star mergers (Schneider et al., 2014).”
• Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Still higher initial masses (105-170 M⊙) for the stars in NGC3603 and even higher in R136 (165-320 M⊙) have been suggested (Crowther et al. 2010).”
• A PANCHROMATIC VIEW OF THE RESTLESS SN 2009ip REVEALS THE EXPLOSIVE EJECTION OF A MASSIVE STAR ENVELOPE (2013, background): “This implies Lbol > 2× 106 L , thus rivaling the most luminous stars ever discovered (e.g. Crowther et al. 2010).”
• The great escape: how exoplanets and smaller bodies desert dying stars (2011, background): “However, observations do suggest that stars up to 300 M exist (Crowther et al. 2010).”
• Stellar population effects on the inferred photon density at reionization (2015, background): “There is now observational evidence a small number of stars at M=100-300M⊙ in nearby star forming regions (Crowther et al. 2010).”
• Evolutionary roads leading to low effective spins, high black hole masses, and O1/O2 rates for LIGO/Virgo binary black holes (2017, methodology): “We adopted a rather conservative maximum initial mass for the stars: MZAMS < 150 M , although there appears to be evidence that stars with masses of ∼200−300 M may exist even in the local Universe (Crowther et al. 2010).”
• Massive black hole binaries from runaway collisions: the impact of metallicity (2016, background): “First, the most massive stars MNRAS 000, 000–000 (0000) in the local Universe are often found in binary systems (Crowther et al. 2010).”
• Evolution and fate of very massive stars (2013, methodology): “Core-collapse SNe produce of the order of 0.05 M (ejected masses) of iron, 1 M of each of the α-elements.”
• The effect of pair-instability mass loss on black-hole mergers (2016, methodology): “Such massive stars exist (Crowther et al. 2010) and were already considered in terms of BH formation (Yusof et al. 2013) and as progenitors of massive BH-BH mergers (Belczynski et al. 2014; Marchant et al. 2016).”