Galaxies in the early universe have less metal than expected. Observations from the James Webb Space Telescope (JWST) show that these galaxies do not follow the basic rules of galactic evolution that operate in the relatively nearby and therefore relatively recent Universe.
caspar heinz Researchers from the University of Copenhagen in Denmark used JWST to study 16 galaxies. All of these galaxies formed within the first 750 million years after the Big Bang. They found that these galaxies had fewer heavy elements, or metals, as they are called in astronomy, than expected based on our understanding of closer galaxies.
“The physics driving galaxy formation and evolution during these early epochs must have been very different from what we observe today,” Heinz says. Some simulations have predicted this phenomenon and other observations have suggested it, but this is the first hard evidence.
This observation suggests that these galaxies are diluted by pure gas without metals. They are probably born with relatively low, but not abnormally low, metal abundances, as we would expect. It then swallows gas from the surrounding intergalactic medium.
This means that these galaxies are not as independent from their surroundings as those seen in the nearby Universe. “If we want to understand the evolution of galaxies, “In the earliest times, we can no longer treat them as separate ‘ecosystems’,” says Heinz. “We need to consider the close relationship with the surrounding intergalactic and ring galactic gas.”
This is not the first anomaly that JWST has discovered in early galaxies. The telescope also discovered that they are much larger and more abundant than we expected. The new observations may actually make the problem of our understanding even worse, because the large amounts of gas needed to dilute early galaxies make them even more astonishingly large.
- james webb space telescope