Observations of 30 Doradus, a star-forming region in a nearby galaxy called Large Magellanic Cloud, reveal that massive stars are more prevalent than models have predicted.

30 Doradus, also known as the Tarantula Nebula or NGC 2070, resides 170,000 light-years away in the Large Magellanic Cloud, a small satellite galaxy to our Milky Way.

It is an example of an HII region — a large cloud of partially ionized hydrogen within which new stars are being born.

Star formation in 30 Doradus started tens of millions of years ago, though it was not confined to a specific region. Instead, as enough gas accumulated, pockets of star birth burst to life erratically, like the finale of a fireworks show.

“We were astonished when we realized that 30 Doradus has formed many more massive stars than expected,” said Dr. Fabian Schneider, from the University of Oxford, UK.

As part of the VLT-FLAMES Tarantula Survey, Dr. Schneider and colleagues used ESO’s Very Large Telescope to observe nearly 1,000 stars in 30 Doradus.

They used detailed analyses of about 250 stars with masses between 15 and 200 times the mass of our Sun to determine the distribution of massive stars born in the region – the so-called initial mass function (IMF).

“We have not only been surprised by the sheer number of massive stars, but also that their IMF is densely sampled up to 200 solar masses,” said Dr. Hugues Sana, from the University of Leuven, Belgium.

Until recently, the existence of stars up to 200 solar masses was highly disputed, and our study shows that a maximum birth mass of stars of 200-300 solar masses appears likely.

“Our results suggest that most of the stellar mass is actually no longer in low-mass stars, but a significant fraction is in high-mass stars,” said Dr. Chris Evans, from the Science and Technology Facilities Council’s UK Astronomy Technology Centre.

Stars are cosmic engines and have produced most chemical elements heavier than helium, from the oxygen we breathe every day to the iron in our blood. During their lives, massive stars produce copious amounts of ionizing radiation and kinetic energy through strong stellar winds.

The ionising radiation of massive stars was crucial for the re-brightening of the Universe after the so-called Dark Ages, and their mechanical feedback drives the evolution of galaxies.

“To quantitatively understand all these feedback mechanisms, and hence the role of massive stars in the Universe, we need to know how many of these behemoths are born,” said Dr. Philipp Podsiadlowski, from the University of Oxford.

“Our results have far-reaching consequences for the understanding of our cosmos: there might be 70% more supernovae, a tripling of the chemical yields and towards four times the ionizing radiation from massive star populations,” Dr. Schneider added.

“Also, the formation rate of black holes might be increased by 180%, directly translating into a corresponding increase of binary black hole mergers that have recently been detected via their gravitational wave signals.”

The research is published in the journal Science.

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F.R.N. Schneider et al. 2018. An excess of massive stars in the local 30 Doradus starburst. Science 359 (6371): 69-71; doi: 10.1126/science.aan0106