Superstars shaped the universe
Many more stars million times brighter than the Sun overturn past models.
Our Sun is commonly held to be an average sized star. Sadly, it now appears to be a pipsqueak compared to the monsters that ruled the early cosmos.
That’s the finding of a team of international astronomers who pointed the European Southern Observatory’s Very Large Telescope in Chile at the Large Magellanic Cloud, a galaxy about 160,000 light-years away.
The team examined about 800 stars in a ‘starburst’ region called 30 Doradus or the Tarantula Nebula, and were surprised to count dozens of stars 30 to 200 times the mass of the Sun.
Their findings, published in the journal Science, challenge the belief that small stars comprised the vast majority of primordial stellar matter. If the findings from this nearby galaxy hold true for more distant, early galaxies, it has major ramifications for understanding the history of the universe.
After the initial fury of the Big Bang, cosmologists believe that the early universe was a cold, dark place populated by clouds of neutral hydrogen and helium. The ‘dark age’ ended a few hundred million years later, as gravitational attraction between the atoms caused them to slowly clot and form the first stars and galaxies. As these stars ignited, they not only brought light back to the Universe, but showered it with ionizing radiation, stellar winds and shock waves from exploding supernovae. These pressed back against the condensing gas, putting the brakes on the rate of star formation.
This “regulated” the star-forming process so it continues today, says the study’s lead author, Fabian Schneider of the University of Oxford. “Otherwise it would have stopped early on.”
The discovery of so many superstars suggests that these giants may have played a larger role in this process than previously realised. That’s because the impact of these massive stars lies not so much in their size but their brightness.
A star 100 times the mass of the Sun would be a million times brighter, Schneider explains.
Such stars are ‘cosmic engines’, blasting out ionising radiation and strong stellar winds. They also die young in massive explosions that create black holes and neutron stars, and disperse elements – such as carbon, oxygen, silicon and iron – necessary to create planets and life.
The biggest caveat to the new find is that the Tarantula Nebula may not be typical of star-forming regions in the earliest galaxies. For one thing, it has too many heavier elements, typical of more mature galaxies.
But if the predictions are correct, and superstars were common, that means the universe will also have more black holes than predicted since they are the end stage of massive stars. According to Schneider, the formation rate might be 180% higher.
If the new paper – “An excess of massive stars in the local 30 Doradus starburst” – is correct, we should detect more gravitational waves from black hole mergers, says Brad Tucker, an astrophysicist and cosmologist at Australian National University: “Simply put, more larger stars equals a more exciting universe.”