Massive stars many times larger than the sun are even bigger, and far more common, than previously believed. New research published in Science has shown these “cosmic engines” could reach 200 to 300 times the size of the sun—a feat previously believed impossible by many astronomers. Their surprising abundance could rewrite our understanding of the universe itself.
Stars that hold more than eight to 10 times the mass of the sun are often called “massive.” Their explosive lifecycles shape the very fabric of our universe by producing black holes, neutron stars and strong stellar winds.
“These massive stars are cosmic engines that have helped to transform the pristine universe [to] the one we live in today,” lead study author and physicist Fabian Schneider from the University of Oxford explained to Newsweek.
But until recently, said Schneider, many astronomers did not think a star approaching 200 times the mass of the sun was even possible. In this new study, the team estimates that the maximum mass of stars at birth could be up to 300 solar masses.
The Tarantula Nebula
The researchers used the Very Large Telescope in Chile to scour a plot of sky known as 30 Doradus, or the “Tarantula nebula.” This section of space is home to some of the largest and fastest stars ever observed, and is marked by extreme starburst events from the early universe. This enormous stellar nursery sits 180,000 light years away in the Large Magellanic Cloud.
The international team used spectroscopy to determine the surface temperature, surface acceleration, rotation rate and luminosity of the stars in 30 Doradus.
“We split the light into its individual wavelength components,” Schneider explained. “This gives a characteristic 'fingerprint' of stars.”
This information enabled the researchers to further determine the age and mass of stars by comparing their data to theoretical models that can predict the appearance of stars.
Schneider and his team have spent years building up a range of analytical tools that enabled this breakthrough discovery. The spectroscopy data meant they could determine the “initial mass function” (IMF) of each star. The IMF, Schneider explained, is central to astrophysical research because it provides data that can shine light on how mass is distributed in a group of stars. Schneider and team believe this is the first time such a determination has been made using spectroscopy alone.
The researchers were stunned to confirm nearly 1,000 stars with masses between 15 and 200 times that of the sun. “There is a significant excess of massive stars in 30 Doradus,” said Schneider. The team estimates that the nebula produces 70 percent more supernovae than previous calculations assumed. The black hole formation rate is nearly tripled in the new estimate. But how 30 Doradus accomplished this feat is unknown.
“We still do not understand how this was possible,” he said.
A “stepping stone” to the distant universe
The team’s work was limited to one local star nursery, but the implications of their results should reach throughout space.
“If nature managed to form so many stars there, it will also be able to do so in other, similar regions in the universe,” Schneider said. “30 Doradus, thus, is a stepping stone to the distant universe."
Having an accurate representation of massive stars is essential to understanding the universe. These stars have a “profound impact” on their surroundings because they produce strong stellar winds, extreme radiation and supernova explosions, features that are crucial for the evolution of galaxies.
“For all of these applications,” Schneider said, “one needs to understand how many massive stars are born over cosmic time.”