Three-color images of the galaxy candidate identified by the study, based on a composite of different color filters. The left image appears as red due to the very high redshift, resulting in no detected flux in the filters for blue and green colors. The right image shows an approximated "true" color image. The scale bar corresponds to 1 kilo-parsec. Credit: ApJl Dec 2022 Vol.940 / CC BY 4.0.
A bright galaxy dating back to 400 million years after the Big Bang has been detected by the James Webb Space Telescope (JWST), according to a study in The Astrophysical Journal Letters, co-authored by Italian astronomers1.
The galaxy is part of a cluster the telescope has been observing in the past year, that belong to an age of the Universe in which such big, bright galaxies are not expected by the standard cosmological theory. Theoreticians are scrambling to explain these findings.
The JWST, launched in December 2021, allows a view deeper in time than its predecessor Hubble. It captures images of galaxies with a larger redshift (the changes in the radiation from distant objects due to the accelerated expansion of the Universe), that existed in a remote time.
Since the first results of the JWST have started to flow, scientists have been surprised by images of bright galaxies with redshift above 10, corresponding to less than half-a- billion years after the Big Bang. The one reported in the article has an estimated redshift of 12. This means the image represents the galaxy as it looked like around 400 million years after the beginning of the Universe.
In these preliminary stages of data analysis, the redshift is estimated by photometry, which is a processing of the pictures themselves, and may contain some errors. This is why scientists refer to these findings as ‘candidate’ galaxies. The studied galaxy was presented in a preprint this summer with a redshift of 14, and tagged as the oldest ever observed, but this estimate was later corrected to 12.
The definitive measure should be provided by a more detailed analysis of the light emitted by the galaxy called spectrometry.
“It’s unexpected to find so many bright galaxies in the first billion years after the Big Bang, when just a small percentage of the stars had formed”, says Marco Castellano, a researcher at Osservatorio Astronomico di Roma-INAF, and co-author of the paper.
“The standard cosmological model says that big galaxies are formed by aggregating smaller ones,” says Andrea Ferrara, a cosmologist at Scuola Normale Superiore di Pisa, who was not involved in the article. Going back in time, we expected to find smaller, fainter galaxies”,
Physicists are putting forward a range of hypotheses to explain JWST’s observations. One possibility is that these galaxies are being spotted by chance at a point when they are in a peak of stellar formation, leading to high brightness. Another option is that they look bright because stellar winds may have removed a lot of dust around them, enhancing their brightness without them being big. It may even be that the JWST has sampled by chance the few patches of the sky where these ‘anomalous’ galaxies are concentrated, and that not many more will be found in larger samples.
If any of these hypotheses is true, the standard model would be preserved. But the theory would be untenable if the JWST finds a lot of galaxies with large redshift that are also very massive.
“It takes a substantial amount of time to start building up a galaxy” says Charlotte Mason, a cosmologist at the University of Copenhagen, who was not involved in the article. “Even in the case where you assume that all the gas that these galaxies were accreting is converted into star, you could still not form such a mass in that short period of time”.
If that were the case, one possible explanation would imply pushing back the date of the Big Bang. That would allow for a large enough timelapse after the beginning of the Universe to grow such large galaxies. “It’s exciting to be in a period that is questioning the theory”, says Mason.
