An excess of massive stars in the local 30 Doradus starburst

Two waves of massive stars running away from the young cluster R136

Massive stars are predominantly born in stellar associations or clusters1. Their radiation fields, stellar winds and supernovae strongly impact their local environment. In the first few million years of a cluster's life, massive stars are dynamically ejected and run away from the cluster at high speed2. However, the production rate of dynamically ejected runaways is poorly constrained. Here we report on a sample of 55 massive runaway stars ejected from the young cluster R136 in the Large Magellanic Cloud. An astrometric analysis of Gaia data3-5 reveals two channels of dynamically ejected runaways. The first channel ejects massive stars in all directions and is consistent with dynamical interactions during and after the birth of R136. The second channel launches stars in a preferred direction and may be related to a cluster interaction. We found that 23-33% of the most luminous stars initially born in R136 are runaways. Model predictions2,6,7 have significantly underestimated the dynamical escape fraction of massive stars. Consequently, their role in shaping and heating the interstellar and galactic media and their role in driving galactic outflows are far more important than previously thought8,9.

Star Formation in the Ultraviolet

With the launch of JWST and the upcoming installation of extremely large telescopes, the first galaxies in our Universe will finally be revealed. Their light will be dominated by massive stars, which peak in in the ultra-violet (UV) part of the electromagnetic spectrum. Star formation is the key driver of the evolution of our Universe. At young ages, within 10 Million years, both high and low mass stars generate complex UV emission processes which are poorly understood yet are vital for interpreting high red-shift line emission. For these reasons, the Hubble Space Telescope (HST) will devote 1000 orbits to obtaining a UV Legacy Library of Young Stars as Essential Standards (ULLYSES). The purpose of this Overview is to outline the basic physical principles driving UV emission processes from local (within 100 parsecs of) star formation, ranging from huge star-forming complexes containing hundreds of massive and very-massive stars (VMS), such as 30 Doradus (the Tarantula Nebula) in the neighboring Magellanic Clouds (only 50 kpc away), to galaxies near and far, out to the epoch of Cosmic Reionization.

Massive Stars in the Tarantula Nebula: A Rosetta Stone for Extragalactic Supergiant HII Regions

A review of the properties of the Tarantula Nebula (30 Doradus) in the Large Magellanic Cloud is presented, primarily from the perspective of its massive star content. The proximity of the Tarantula and its accessibility to X-ray through radio observations permit it to serve as a Rosetta Stone amongst extragalactic supergiant HII regions since one can consider both its integrated characteristics and the individual properties of individual massive stars. Recent surveys of its high mass stellar content, notably the VLT FLAMES Tarantula Survey (VFTS), are reviewed, together with VLT/MUSE observations of the central ionizing region NGC 2070 and HST/STIS spectroscopy of the young dense cluster R136, provide a near complete Hertzsprung-Russell diagram of the region, and cumulative ionizing output. Several high mass binaries are highlighted, some of which have been identified from a recent X-ray survey. Brief comparisons with the stellar content of giant HII regions in the Milky Way (NGC 3372) and Small Magellanic Cloud (NGC 346) are also made, together with Green Pea galaxies and star forming knots in high-z galaxies. Finally, the prospect of studying massive stars in metal poor galaxies is evaluated.

Response to Comment on "An excess of massive stars in the local 30 Doradus starburst"

Farr and Mandel reanalyze our data, finding initial mass function slopes for high-mass stars in 30 Doradus that agree with our results. However, their reanalysis appears to underpredict the observed number of massive stars. Their technique results in more precise slopes than in our work, strengthening our conclusion that there is an excess of massive stars (>30 solar masses) in 30 Doradus.

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time

All measurements of cosmic star formation must assume an initial distribution of stellar masses-the stellar initial mass function-in order to extrapolate from the star-formation rate measured for typically rare, massive stars (of more than eight solar masses) to the total star-formation rate across the full stellar mass spectrum ¹ . The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time ² . Classical determinations of the stellar initial mass function in local galaxies are traditionally made at ultraviolet, optical and near-infrared wavelengths, which cannot be probed in dust-obscured galaxies^2,3, especially distant starbursts, whose apparent star-formation rates are hundreds to thousands of times higher than in the Milky Way, selected at submillimetre (rest-frame far-infrared) wavelengths^4,5. The ¹³C/¹⁸O isotope abundance ratio in the cold molecular gas-which can be probed via the rotational transitions of the ¹³CO and C¹⁸O isotopologues-is a very sensitive index of the stellar initial mass function, with its determination immune to the pernicious effects of dust. Here we report observations of ¹³CO and C¹⁸O emission for a sample of four dust-enshrouded starbursts at redshifts of approximately two to three, and find unambiguous evidence for a top-heavy stellar initial mass function in all of them. A low ¹³CO/C¹⁸O ratio for all our targets-alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way ⁶ -implies that there are considerably more massive stars in starburst events than in ordinary star-forming spiral galaxies. This can bring these extraordinary starbursts closer to the 'main sequence' of star-forming galaxies ⁷ , although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.