The Webb Space Telescope has helped astronomers peer into the distant cosmos, revealing a population of galaxies that had reached their massive size just 500 million years after the Big Bang. A closer look at those ancient galaxies suggests they may be even larger than previously estimated, challenging current models of the early universe. In a study published last week in Nature Astronomy, researchers discovered a previously hidden population of tiny, faint stars in the most massive galaxies of the early universe. The new findings suggest that those galaxies contained many more smaller stars than expected and are even more massive than scientists once thought. Hidden stars The team of researchers behind the new study examined nine massive galaxies that had stopped forming new stars billions of years ago. Using Webb’s deep spectra, combined with ground-based observations from the Very Large Telescope, the researchers attempted to measure the number of small, faint stars compared to the giant, bright ones residing in those galaxies. To do this, they observed the different spectrums of light emanating from galaxies and looked for subtle color differences. Bright stars tend to dominate the light, making observations of their smaller, fainter counterparts much more challenging. “If a galaxy were a city, the brightest stars would be the skyscrapers that immediately attract attention from afar,” Chloe Cheng, a researcher at Leiden University and lead author of the study, said in a statement. “We needed not only a telescope capable of magnifying very distant galaxies,” explained co-author Martje Slob of Leiden University, “but also exceptional quality spectra and new analysis techniques to reliably detect the subtle signatures of faint, low-mass stars hidden within these cosmic titans.” The team’s models revealed that “a much larger population of low-mass stars is hidden by these rare, bright stars, like houses hidden between skyscrapers,” Cheng added. The results suggest that these galaxies are much more massive than previous estimates had predicted. One particular galaxy that formed less than one and a half billion years after the Big Bang may be four times more massive than previously believed. Galactic mystery Scientists had previously assumed that stars form in equal proportions throughout the universe, but the new results revealed that the most massive galaxies in the early universe contained a much larger population of low-mass stars than smaller galaxies. Since Webb began observing the early universe, scientists have discovered that ancient galaxies were already much larger than their model had previously suggested. The new findings therefore have implications for our understanding of the early universe and how the oldest galaxies formed. “This result shows that much more mass is hidden in low-mass stars than previously thought,” said Mariska Kriek, a researcher at Leiden University who led the research. “This has consequences for many areas of astronomy. For example, as many planets orbit low-mass stars, this could even indicate that more planets formed in the early universe than we had previously assumed.”
