An article published in “The Astrophysical Journal Letters” reports a study indicating that the early universe was much brighter than predicted by simulations based on current cosmological models. A team of researchers coordinated by the Center for Astrobiology (CAB) in Madrid, Spain, used observations conducted with the James Webb Space Telescope to examine galaxies that formed between 200 and 500 million years after the Big Bang. The combination of observations conducted with the NIRCam instrument and the MIRI Deep Imaging Survey (MIDIS) of the Hubble Ultra Deep Field (HUDF) on a sample of 44 primordial galaxies shows their surprising brightness and compactness.
The image (Courtesy Pierluigi Rinaldi, Rafael Navarro-Carrera, Pablo G. Pérez-González) shows the so-called ultradeep field used in the MIDIS survey and on the right, some of the primordial galaxies at the center of this study are highlighted in the circles.
Many astronomers are trying to figure out when stars and galaxies started forming after the Big Bang. Primordial galaxies were discovered and studied in recent decades using the Hubble Space Telescope and the beginning of the James Webb scientific mission enabled even more detailed studies to begin. That’s bringing improvements in comparisons between cosmological simulations such as Illustris and EAGLE created using current models and collected data.
The James Webb Space Telescope’s NIRCam and MIRI instruments showed that a sample of 44 galaxies that formed within the first 500 million years of the universe’s life is brighter and more compact than predicted by cosmological models. In particular, ultraviolet photons turn out to be ten times more numerous than predicted.
Ultraviolet photons can be generated by hot, massive young stars that have short and intense lifetimes. They can also be generated by the activity of supermassive black holes heating the materials around them. These galaxies are also two or three times more compact than expected and this feature could also be caused by the influence of supermassive black holes. However, this possible answer leads to other questions.
Supermassive black holes were already observed in the early universe and it’s still difficult to explain how they formed so quickly from an astronomical point of view. Some theories were proposed in recent years to try to explain how a black hole can reach a mass millions of times the Sun’s just a few hundred million years after the Big Bang. As with early galaxies, the problem was obtaining observations of sufficient quality to test the various theories.
This study is based on a limited sample of galaxies for which the James Webb Space Telescope just started providing data for analysis. The combination of the NIRCam and MIRI instruments made it possible to detect galaxies ten times fainter than those studied during the first six months of Webb’s science mission. This shows how the tune-up of the instruments and their use by researchers offers considerable room for improvement.
The MIDIS survey offered surprises and new questions. Observing other primordial galaxies will help create statistics about their characteristics, in particular their brightness and their compactness. Models of the formation of massive stars in these galaxies may need to be revised, and new information could emerge crucial to understanding the quick formation of primordial supermassive black holes.
