Posted in | Quantum Physics

Astronomers Reveal Overabundance of Massive Stars in a Neighboring Galaxy

An 'astonishing' overabundance of massive stars has been revealed in a neighboring galaxy by a global team of astronomers.

This discovery in the gigantic star-forming region 30 Doradus in the Large Magellanic Cloud galaxy, is known to have 'far-reaching' consequences for the understanding of how stars changed the pristine Universe into the one that humans live in today.

The results have been featured in the journal Science.

We were astonished when we realized that 30 Doradus has formed many more massive stars than expected.

Fabian Schneider, Key Author

The team, as part of the VLT-FLAMES Tarantula Survey (VFTS), made use of ESO's Very Large Telescope in order to observe almost 1,000 massive stars in 30 Doradus, a gigantic stellar nursery also called the Tarantula nebula. The team used in depth analyses of almost 250 stars with masses between 15 and 200 times the mass of the Sun in order to define the distribution of massive stars born in 30 Doradus - the so-called initial mass function (IMF).

Massive stars are mainly vital for astronomers due to their enormous impact on their surroundings (called their 'feedback'). They are capable of exploding in spectacular supernovae towards the end of their lives, developing some of the most interesting objects in the Universe - black holes and neutron stars.

Co-author Hugues Sana from the University of Leuven, Belgium said: '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.' Until recently, the presence of stars up to 200 solar masses was greatly disputed, and the study demonstrates that a maximum birth mass of stars of 200-300 solar masses appears likely.

In most parts of the Universe analyzed by astronomers to date, stars have become rarer the more gigantic they are. The IMF forecasts that most stellar mass is in low-mass stars and that less than 1% of all stars have originated with masses in excess of 10 times that of the Sun. Measuring the proportion of massive stars is very difficult - mainly due to their scarcity - and there are just a handful of places in the local Universe where this can be performed.

The team employed to 30 Doradus, the largest local star-forming region, which hosts some of the most gigantic stars ever found, and determined the masses of massive stars with exceptional observational, statistical and theoretical tools. This huge sample permitted the scientists to derive the extremely accurate high-mass segment of the IMF to date, and to demonstrate that massive stars are indeed much more abundant than earlier thought. Chris Evans from the Science and Technology Facilities Council's UK Astronomy Technology Centre, the chief investigator of VFTS and a co-author of the study, said: “In fact, 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.”

Stars are considered to be cosmic engines and have generated most chemical elements heavier than helium, from the oxygen humans breathe daily to the iron present in their blood. During their lives, gigantic stars generate ample amounts of kinetic energy and ionizing radiation via strong stellar winds. The ionizing radiation of gigantic stars was important for the re-brightening of the Universe after the Dark Ages and their mechanical feedback motivates the evolution of galaxies. Philipp Podsiadlowski, a co-author of the study from the University of Oxford, said: “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.”

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. 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.

Fabian Schneider, Key Author

The team's research presents a number of open questions, which they plan to examine in the future: how common are the findings, and what are the consequences of this for the evolution of the cosmos and the occurrence of gravitational wave and supernovae events?

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