This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers have discovered that the most massive galaxies in the early universe contain far more small stars than expected. As a result, these early galaxies were likely much more massive than initial measurements suggested.
This discovery challenges current understanding about how the first galaxies formed. The results are published today in Nature Astronomy. An international team of researchers led by scientists at Leiden University leveraged the James Webb Space Telescope (JWST) to make this discovery.
The team studied nine massive, mature galaxies that ceased forming stars billions of years ago, combining extremely deep JWST spectra with previous ground-based observations from the Very Large Telescope. The researchers used these observations to reliably determine the proportions of tiny, faint stars and giant, bright stars present in such distant galaxies for the first time. To achieve these measurements, astronomers split the light from a galaxy into a spectrum, in which subtle differences in color reveal the types of stars within the galaxy.
This spectrum is typically dominated by massive, bright stars, making the much fainter, low-mass stars extremely challenging to detect. "If a galaxy were a city, the brightest stars would be the skyscrapers that immediately catch your eye from afar," says lead author Chloe Cheng from Leiden University, who earned her Ph.D. in June based in part on this research. "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." To estimate the unseen mass locked up in small, faint stars, astronomers historically assumed that stars formed in roughly the same proportions everywhere in the universe. These new results challenge that assumption and show that the most massive galaxies in the early universe contain a much larger fraction of low-mass stars than less massive galaxies, such as our own Milky Way. For one of the galaxies in the sample, the effect is particularly striking.
That galaxy likely formed less than one and a half billion years after the Big Bang and may be as much as four times more massive than previous estimates indicated. "Until recently, measurements like these were simply impossible," says co-author Martje Slob from Leiden University. "We needed not only a telescope capable of magnifying very distant galaxies, but also spectra of exceptional quality and new analysis techniques to reliably detect the subtle signatures of faint, low-mass stars hidden within these cosmic titans." This discovery has crucial implications for our understanding of the early universe.
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