Galaxies in the early universe have fewer metals than expected. Observations from the James Webb Space Telescope (JWST) have shown that these galaxies don’t follow a fundamental rule about galaxy evolution that is at work in the relatively nearby – and therefore relatively recent – universe.
Kasper Heintz at the University of Copenhagen in Denmark and his colleagues used JWST to look at 16 galaxies, all of which formed within the first 750 million years after the big bang. They found that these galaxies had fewer heavy elements, or metals as they’re called in astronomy, than we’d expect based on our understanding of closer galaxies.
“The physics that drives galaxy formation and evolution at these early epochs must be drastically different than what we observe today,” says Heintz. This was predicted by some simulations and there were some hints in other observations, but this is the first solid evidence.
The observations suggest that these galaxies are diluted by pristine gas without metals in it. They’re most likely born as we’d expect, with relatively low metal abundances but not abnormally low, and then they gobble up gas from the surrounding intergalactic material.
This means that these galaxies are not as independent of their surroundings as the ones we see in the nearby universe. “If we are to understand galaxy evolution at the earliest epochs, we can no longer treat them as individual ‘ecosystems’,” says Heintz. “We have to take into account their intimate connection to the surrounding intergalactic or cirgumgalactic gas.”
This isn’t the first anomaly spotted in early galaxies – JWST has also found that these galaxies are far more massive and abundant than we’d expect. These new observations might actually make that problem with our understanding worse, because the huge amounts of gas required to dilute early galaxies would make them even more shockingly massive.
- James Webb space telescope