Astronomers using the James Webb Space Telescope and the Very Large Telescope have discovered that massive early galaxies formed within 500 million years of the Big Bang contain a hidden population of low-mass stars, suggesting these ancient cosmic systems are more massive than previously estimated.
The Webb space telescope has helped astronomers peer into the distant cosmos, revealing a population of galaxies that had grown into their massive size within a mere 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 uncovered a previously hidden population of tiny, faint stars in the most massive galaxies of the early universe. The new findings suggest those galaxies contained a lot more smaller stars than expected and are even more massive than scientists once thought.
Hidden Stars and Cosmic Cities
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 sought to measure the amount of tiny, faint stars compared to giant, bright ones residing in those galaxies. To do that, they observed the different spectrum of light emanating from the galaxies and looked for subtle differences in color. Bright stars tend to dominate the light, making observations of their smaller, faint counterparts much more challenging.
If a galaxy were a city, the brightest stars would be the skyscrapers that immediately catch your eye from afar,
Chloe Cheng, a researcher from Leiden University and lead author of the study, said in a statement.
We needed not only a telescope capable of magnifying very distant galaxies,
co-author Martje Slob, of Leiden University, explained, 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.
The team’s models revealed a far more numerous population of low-mass stars is concealed by those rare, bright stars, like houses hidden between skyscrapers,
Cheng added. The results suggest that those galaxies are much more massive than previous estimates had predicted. One galaxy in particular that had formed less than one and a half billion years after the Big Bang may be four times more massive than previously believed.
Galactic Mystery and Proportions
Scientists had previously assumed that stars form in equal proportions across 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 first began observing the early universe, scientists learned that ancient galaxies were already much larger than their model had previously suggested. The new findings, therefore, have implications of our understanding of the early universe and how the most ancient galaxies formed.
Ferrara’s team is exploring the infancy of the universe, pushing the frontier a little bit further,
as he puts it, to get closer to the Big Bang and discover the first stars that formed within the earliest galaxies. Currently, Ferrara’s team is observing galaxies that were already in place and functioning about 300 million years after the Big Bang. One of their latest discoveries is that these baby galaxies are rich in heavy elements and dust. His team is currently studying the most distant galaxy we know, called GS-z14-0, or GS14 for short. Ferrara explains that they didn’t expect to find a galaxy so large and bright in this extremely early phase of cosmic evolution.
High Spatial Density in Baby Galaxies
Observations reveal that these early galaxies are small – almost 100 times smaller than those around us. Galaxies grow through a process of coagulation,
Ferrara explains. They start as tiny pieces; the very first galaxies formed, then merged over time to create larger and larger galaxy systems.
Due to their small size, the stars are heavily packed, or more rigorously, their spatial density is very high.
Learning more about the first galaxy has become possible with the James Webb Space Telescope (JWST). Ferrara notes that now is the right time to make discoveries and close the circle, since the JWST will not last forever.
This result shows that much more mass than previously thought is hidden in low-mass stars,
Mariska Kriek, a researcher at Leiden University who led the research. That 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.
