JWST spectra find hidden dwarf stars that could triple mass estimates for early galaxies

By the Everything Space news desk · 24 Aug 2026 · written from the sources below

If the earliest massive galaxies also hide swarms of faint low-mass stars, their stellar masses may be three to four times higher, sharpening a puzzle about how fast galaxies grew.

Astronomers using the James Webb Space Telescope report that some massive galaxies contain far more small, dim stars than standard assumptions allow, a finding that could inflate stellar mass estimates for the puzzlingly large galaxies seen in the young Universe.

The work, led by Mariska Kriek of Leiden Observatory with Chloe Cheng of Leiden University, targeted nine massive galaxies observed as they appeared roughly seven billion years ago. The team gathered unusually deep spectra with JWST and combined them with earlier data from the Very Large Telescope in Chile.

Faint stars such as red dwarfs contribute little light but can hold a large share of a galaxy's mass. Because individual dwarfs cannot be resolved at such distances, their numbers are normally inferred by assuming galaxies produce stars in the same proportions seen in the Milky Way — a distribution known as the initial mass function. Low-mass stars do, however, absorb light at particular wavelengths, leaving faint imprints in a galaxy's combined spectrum.

Measuring those features, the team found several galaxies with substantially more low-mass stars than the Milky Way recipe predicts, a pattern described as a bottom-heavy initial mass function. Cheng compared a galaxy to a city in which the brightest stars are the skyscrapers that dominate the distant view, while a much larger population of small stars sits hidden between them.

Two of the oldest galaxies in the sample appear to have formed very early and are plausible descendants of the extremely massive galaxies JWST has identified within roughly the first billion years after the Big Bang. Those objects are already hard to explain, since there seems to have been too little time for them to assemble so much mass. If they share the same abundance of faint stars, their stellar masses could be three to four times larger than current estimates.

Kriek noted that because low-mass stars frequently host planets, the result may also hint that more planets formed in the early Universe than assumed. The link to the earliest galaxies remains an inference, however: the team studied likely descendants rather than the ancient galaxies themselves. Future observations will attempt the harder measurement of stellar populations closer to the era when those first galaxies took shape.

Written in Everything Space’s own words by our news-desk model from the sources above, and checked against them in code: every number in this report appears in its sources, and no sentence is copied from them.