Early Galaxies May Be Four Times More Massive Than Previously Thought

Astronomers have discovered that some of the largest galaxies in the early universe contain a significantly greater number of small, faint stars than previously understood. This hidden population of stars suggests these ancient galaxies could be three to four times more massive than earlier estimates indicated.

This finding, made by an international team including researchers from Penn State, presents a new challenge to current theories regarding the formation and evolution of the first galaxies. The results were published in *Nature Astronomy*.

The research utilized observations from the National Aeronautics and Space Administration's (NASA) James Webb Space Telescope (JWST) to examine nine massive, mature galaxies that ceased forming stars billions of years ago. By combining JWST data with earlier ground-based observations from the Very Large Telescope, scientists were able to estimate the relative proportions of small, faint stars and larger, brighter stars in these distant galaxies.

Astronomers determined the stellar composition by analyzing the spectrum of light emitted by each galaxy. Small variations in color within the spectrum reveal the types of stars present. While large, luminous stars dominate the light, smaller stars are much dimmer and more difficult to detect. The Penn State team provided expertise in modeling the light from these galaxy systems.

Traditionally, astronomers have assumed that stars formed in similar proportions throughout the universe when estimating the mass of small, faint stars. This new research challenges that assumption. The most massive galaxies in the early universe appear to have a much higher proportion of low-mass stars compared to smaller galaxies like the Milky Way.

One galaxy, formed less than one and a half billion years after the Big Bang, stood out as potentially four times more massive than prior calculations suggested. This discovery has significant implications for understanding how galaxies developed in the early universe and could also suggest that planets around low-mass stars were more common in the early universe than previously believed.