Astronomers unexpectedly find an abundance of massive stars

The star-breeding nursery in 30 Doradus. Photo: NASA / ESA Hubble Space Telescope

Extremely massive stars may be more abundant in at least one corner of the universe than astronomers have previously thought, according to new research published today in the Science. The finding, if confirmed elsewhere in the cosmos, could change our understanding about the evolution of galaxies, how these stars brought the universe came out of its dark period, the number of supernovae and the occurrence of black hole mergers in the universe.

"These stars and black holes are responsible for converting the universe into the state we see today," says lead author Fabian Schneider from the University of Oxford. "It is important to know how many progenitor stars may have been out in the universe."

How they did it: Using the Very Large Telescope, astronomers observed about 900 stars in 30 Doradus, a star nursery in the Tarantula Nebula that is part of the Large Magellanic Cloud, a galaxy neighboring our own Milky Way. The proximity of 30 Doradus was key because individual stars could be resolved and the distance of the stars was known so their brightness could be calculated, says Schneider.

They analyzed the spectra of the stars to determine their temperature, the acceleration due to gravity on their surface and other information about the stars that allowed them to calculate their mass. By comparing those parameters to theoretical models, they then calculated the age of the stars.

What they found: Focusing on the most massive stars — those 15–200 times the mass of our Sun, they discovered about 1/3 more stars above 30 solar masses than predicted by some star formation models. Other theories have suggested massive stars may be more prevalent than astronomers thought but this is "the first observational hint" that this may be the case, says Schneider.

Ponder this: The diameter of 30 Doradus is 600–700 light years. If you put it at same distance to Earth as the Orion nebula (about 1300 light years away), Schneider calculates it would cover 60 full moons of the night sky. It would be so bright it would cast shadows.

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