Hidden stars have changed the way we think about the first galaxies in the universe

Astronomers have discovered that the most massive galaxies in the early universe contain many more small stars than previously thought. Because of this, their total mass could be significantly underestimated, and the existing ideas about the formation of the first galaxies require revision. About what was seen thanks to the James Webb telescope and why the discovery changes the understanding of the early Universe — in the material of Izvestia.

Giants hidden behind bright stars

An international team led by scientists at Leiden University has studied nine massive mature galaxies in the early universe that stopped forming new stars billions of years ago. For the study, the results of which are published in the journal Phys.org The astronomers combined extremely deep spectra obtained with the James Webb telescope with ground-based observations using a Very Large Telescope.

For the first time, researchers have been able to reliably determine the ratio of small, dim stars to large, bright stars in such distant galaxies. To do this, the scientists decomposed the light of the galaxies into a spectrum: small differences in color make it possible to determine which types of stars are inside the object. However, bright, massive stars usually dominate the spectrum and make low-mass stars extremely difficult to detect.

According to new calculations, the proportion of low-mass stars in the most massive galaxies of the early Universe is significantly higher than in less massive galaxies, including the Milky Way. Previously, astronomers estimated the hidden mass based on the assumption that stars form in approximately the same proportions throughout the universe. The new results call this assumption into question.

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Why did the first galaxies turn out to be even more massive?

The effect was particularly noticeable for one of the nine galaxies studied. According to the researchers, it formed less than 1.5 billion years after the Big Bang, and its mass may be up to four times greater than previous estimates showed.

The discovery is crucial for understanding the early universe. After the launch of the James Webb telescope, astronomers discovered unusually massive and mature galaxies that already existed shortly after the Big Bang. Now, the results of a new study indicate that these objects were probably even more massive than originally thought. Models of galaxy formation will have to explain how so many low-mass stars could have formed at such an early stage in the history of the universe.

According to the researchers, the results may have implications for other fields of astronomy. In particular, since many planets orbit low-mass stars, the detected number of such luminaries may indicate that more planets formed in the early universe than previously thought.

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What now remains to be found out

Until recently, such measurements were practically impossible. They required a telescope capable of exploring extremely distant galaxies, high-quality spectra, and new analysis methods to detect faint signs of low-mass stars hidden behind bright luminaries.

The researchers now plan to apply the developed method to even earlier galaxies. In this way, they hope to approach the era when the first generations of stars and galaxies were forming, and to test how widespread the discovered ratio of low-mass and massive stars is.

Thus, the new data show that a significant part of the mass of early galaxies could remain invisible due to the brightness of rare massive stars. Now scientists have to find out how widespread this ratio was in the universe and how it is related to the formation of the first galaxies.