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A new study based on the first data release of the James Webb Space Telescope (Webb or JWST) has revealed the existence of galaxies nearly as massive as the Milky Way, filled with mature red stars, that seem to have appeared in the universe shortly after the Big Bang. Astronomers are experiencing a headache due to the unexpected presence of these galaxies, whose formation is currently unexplainable.
James Webb Space Telescope Reveals Enormous Mature Galaxies
Galaxies viewed by the James Webb Space Telescope appear as tiny reddish dots due to their distance from Earth. But by analyzing the light emitted by these galaxies, astronomers have established that they are observing them only 500 to 700 million years after the Big Bang. The galaxies found in the Webb images are so shockingly big, and the stars in them are too old, that they are in conflict with existing ideas of how the universe looked and evolved in its early years, and don’t match earlier observations made by Webb’s less powerful predecessor, the Hubble Space Telescope.
Unexpected Mature Galaxies Confound Astronomers
According to Joel Leja, assistant professor of astronomy and astrophysics at Penn State and one of the authors of the study, previous studies of the early universe with Hubble and other instruments tend to find small, blue, baby galaxies at early times: objects that have just recently formed out of the primordial cosmic soup and are themselves building their early stars and structures. However, in ancient galaxies that Webb was built to spot, astronomers had not expected to see old red stars or galaxies more massive than perhaps a billion suns. But those reddish dots revealed in Webb’s deep fields appear 50 times more massive than that, Leja said.
Theories Requiring Revisions to Explain Mature Galaxies
Before astronomers start rewriting cosmology theories to explain how these galaxies came together so quickly after the Big Bang, they will have to ensure the odd red dots they are looking at are not something else. However, most of the alternative explanations also require entirely new concepts, Leja said. For example, stars in the early universe might emit light in exotic ways due to their lack of heavy elements, and perhaps we’re not incorporating those in our models. Or alternatively, perhaps our understanding of how stars form locally, e.g. how many stars form from gas as a function of the mass of the stars, is totally inapplicable in the early universe. These things would also be exciting to discover and would also overturn our understanding of star formation in the early universe — just in a very different way.
Webb Telescope’s Deep Field Images and Future Observations
Webb’s Near Infrared Camera (NIRCam) obtained the images that revealed these puzzling galaxies as part of the Cosmic Evolution Early Release Science (CEERS) program. Astronomers plan to soon turn Webb’s mirror to these galaxies again to, this time, obtain light spectra of those distant dots. Spectra break down the observed light according to its wavelength composition and thus reveal the chemical and physical properties of its source. “The most important thing is that spectra give very precise distances to these objects,” said Leja. “The “distance” and the “identity” of these objects is correlated: if we know the distance, we can pin down the identity, and vice versa. So a spectrum will pretty immediately tell us if our hypotheses are correct.”
Only a little over a month after the launch of the James Webb Space Telescope, scientists already face the challenge of rewriting their theories about the early universe due to the discovery of enormous mature galaxies that they did not expect to find. The existence of these galaxies, filled with red stars, is puzzling astronomers and requiring them to revise their understanding of how the universe evolved in its early years. Webb’s images have revealed galaxies that are nearly as massive as the Milky Way, observed only 500 to 700 million years after the Big Bang. These ancient galaxies are so big and contain stars that are too old to match existing theories of the universe’s evolution, and they don’t match earlier observations made by Hubble.