Distant galaxies could be far more massive than we thought, scientists say.
Far away galaxies, so distant that the light reaching us is from the early universe, could in fact have many more small stars in than we expected, according to a new study. That suggests they might be far more massive than we suspected.
That in turns could change our understanding of how the earliest galaxies formed, the researchers behind the discovery say.
The new findings come from a team of researchers using data from Nasa’s James Webb Space Telescope (JWST). They looked at nine massive, mature galaxies that stopped forming stars billions of years ago.
That allowed them to look at the proportions of tiny, faint stars and giant, bright stars in those distant galaxies.
“These galaxies are different,” said Joel Leja, a professor at Penn State and co-author of the new paper. “They’re different in the way that is really challenging to understand, because they are more massive than we expected — like a lot more massive, they have three or four times more mass than we expected.”
To measure the stars, researchers split the light from the galaxies into a spectrum, using the differences in colours to see the types of stars. Usually, the massive, bright stars dominate, making it harder to see the fainter and lower-mass ones.
“If a galaxy were a city, the brightest stars would be the skyscrapers that immediately catch your eye from afar,” said lead author of the paper Chloe Cheng. “Our models demonstrate that a far more numerous population of low-mass stars is concealed by those rare, bright stars, like houses hidden between skyscrapers.
“As a result, this galaxy turns out to be much more massive than previous estimates suggested.”
In the past, researchers measured the mass of the small, faint stars by assuming that the stars formed in roughly similar proportions across the universe. But the new study suggests that the most massive galaxies in the early universe actually have far more of those lower-mass stars than less massive ones, such as our own Milky Way.
“This discovery has crucial implications for our understanding of the early universe,” said Professor Leja. “Since the launch of JWST, astronomers have found surprisingly massive and mature galaxies that already existed shortly after the Big Bang.
“These very early galaxies are thought to evolve into the type of galaxies studied in this work; adding up to four times more stars to these massive, early-forming galaxies sharpens these tensions further.”
That suggests that these early galaxies were probably even more massive than we have previously thought. Scientists must now work to understand how they were able to form such a vast amount of tiny stars so early in the universe.
The work is reported in a new paper, ‘Hidden mass in early galaxies revealed by bottom-heavy initial mass functions’, published in the journal Nature Astronomy.