Some of the universe’s earliest galaxies appear to have far fewer stars than previously thought, according to observations from the James Webb Space Telescope (JWST). These stars, some of the very first to form, also seem to be dimmer and bluer than previous telescopes indicated.
Images of the universe’s first galaxies have previously only been captured in visible light by the Hubble Space Telescope and in near-infrared frequencies by JWST and the Spitzer space telescope, but the stars in them emit light over other wavelengths too. This means the true nature of these galaxies’ early stars remained elusive.
Now, at the Texas A&M University and his colleagues have used JWST’s mid-infrared instrument, MIRI, to see the longer wavelength light these galaxies emit.
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Initially, these bright bodies appeared much dimmer and “bluer” than they were predicted to be at these wavelengths. “I was actually kind of shocked at first, because a couple of these galaxies we expected to be pretty bright in this longer wavelength data,” says Papovich.
If the data from MIRI had matched previous data in visible and near-infrared light, the researchers would have seen a brighter MIRI signal, which would suggest lots of longer-lived stars like the sun that tend to give off light in longer wavelengths – but they didn’t see this and Papovich and his team calculate that this indicates an order of magnitude fewer stars than previously thought.
The researchers fed the brightness data into models for the early galaxies, and this suggested that, on average, the stars weren’t as old as expected, contained fewer heavy elements and produced more ultraviolet light than stars in galaxies that we see at an older age, such as the Milky Way around us, which is about 13.6 billion years old. The big bang happened about 13.8 billion years ago.
Our best guess is that we are seeing stars when they were just 100 million years old or so, says Papovich, but their light has been travelling to us for nearly 14 billion years.
“Our measurements show the galaxies are forming stars slower than previously thought,” he says.
Early JWST observations had indicated that some very old galaxies had unusually high masses, which didn’t align with current models of galaxy formation and may have meant a drastic rethink was required, but the newer readings allay any fear of a crisis in astrophysics.
“It’s a very early sample, but it already indicates that the crisis that people were starting to talk about is not a real crisis, it’s just due to the lack of these kinds of filters,” says at the University of Oxford.
While the results are still within the bounds of what many models of early galaxies allow, astronomers will now need to run the data through those models to work out how fast the galaxies actually formed, says Cappellari.
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