The first images provided by the JWST telescope (James Webb Space Telescope) two years ago caused a bit of a shock in the world of cosmology: Too many big, bright galaxies appeared too close to the Big Bang. Some of these galaxies seemed to have grown so big and so quickly that simulations couldn’t explain them, and some researchers suggested that this meant something was wrong with the Standard Model of cosmology. What if we had miscalculated our numbers and were pushing back the age of the universe?
While there is nothing more exciting in science than an observation that does not fit the theory, this time the waters seem to be returning to normal and there is a rational explanation for this anomaly. According to the results of a new study published this Monday in the journal The Journal of Astrophysics and led by Katherine Chworowsky of the University of Texas at Austin, some of these early galaxies are much less massive than they initially appeared. Chworowsky finds a possible source of the confusion: For one thing, black holes in some of these galaxies make them appear much brighter and larger than they actually are. For another, the relationships between light and mass in the early universe could have changed, so that the observations would still fit the cosmological model.
One thing the new work highlights is that galaxies that seemed too massive are likely home to black holes that are rapidly consuming gas. Friction in fast-moving gas emits heat and light, making these galaxies appear much brighter than they would if that light were coming from stars alone. This extra light, the authors say, can make galaxies appear to contain many more stars and therefore more mass than we would otherwise estimate. When scientists remove these galaxies, nicknamed “little red dots” (because of their red color and small size), from the analysis, the remaining early galaxies are not too massive to match the Standard Model’s predictions.
We’re seeing even more galaxies than expected, although none of them are massive enough to split the universe.
Katherine Chworowsky
— Researcher at the University of Texas at Austin and leader of the study
“We are seeing even more galaxies than expected, although none of them are massive enough to be observed. to break “The universe,” Chworowsky says. “Ultimately, there is no crisis in terms of the Standard Model of cosmology,” adds Steven Finkelstein, co-author of the study and director of the CEERS study (Science of the Early Version of Cosmic Evolution) of the JWST telescope from which the data is obtained. “Anytime you have a theory that has stood the test of time for so many years, you need overwhelming evidence to rule it out. And that’s just not the case,” he says.
Too many massive galaxies
Although they solved the main problem, there remains a less thorny one: In the JWST data on the early universe, there are still about twice as many massive galaxies as expected from the Standard Model. One possible reason could be that stars formed more quickly in the early universe than they do today. “Maybe in the early universe, galaxies were more efficient at turning gas into stars,” Chworowsky says.
Star formation occurs when hot gas cools enough to succumb to gravity and condense into one or more stars. But as the gas contracts, it heats up, generating outward pressure. In our region of the universe, the balance of these opposing forces tends to make the star formation process very slow. But perhaps, according to some theories, because the early universe was denser than it is today, it was harder to expel gas during star formation, allowing the process to go faster.
A mystery with unsolved margins
For the astrophysicist Hector Vivesresearcher at CEFCA (Centre d’Etudes de Physique du Cosmos de Aragon) who was not involved in the study, it seems that these galaxies biased the observations towards higher masses, and the adjustment of the star formation parameters serves to explain the most extreme results. “The light from the accretion disk of the supermassive black hole can dominate the luminosity of the galaxy and make it difficult to calculate the number of stars and therefore their mass,” he explains. “In this study, they exclude the cases where this happens and find that although there appear to be brighter galaxies than expected in the early universe, they are consistent with our models after small adjustments.”
Sara Cazzoli, a researcher at the Institute of Astrophysics of Andalusia (IAA), believes that the results of the article do not solve the mystery of the evolution of galaxies in the early universe. “However, it lays the foundations for future studies with larger samples,” she says. “These must be accompanied by critical information determined by spectroscopic data on stellar populations, for example.” According to her, the results can be used to improve simulations of the early universe, which is still very little known. “It is interesting to see how knowledge of the populations of these ‘red dots’ is increasing rapidly with the latest results of the analysis of the JWST data,” she points out.
“What this study highlights is the difficulty of making a simple interpretation of data from very distant galaxies for which we do not have sufficiently precise information,” explains Isabel Márquez, an astrophysicist at the Institute of Astrophysics of Andalusia (IAA-CSIC). “In fact, although they continue to see galaxies that are more massive than the model indicates, some adjustments correspond to the models.” This would come from the hypothesis that the relationship between baryonic matter (the atoms that make up the visible universe) and dark matter was different in the younger universe, explains the specialist, or from an even simpler possibility, that the transformation between mass and light was different.
“Today we know well in our universe what mass corresponds to each type of star, with this data and the amount of light we can calculate the mass. What these researchers say is that it is possible that the transformation between light and mass for different types of stars worked differently in the young universe. All this could be solved if we had a way to capture these primitive and distant galaxies with an even greater resolution, which would allow us to analyze the spectrum and solve the enigma, he summarizes. “But they do not have enough light, because they are faint galaxies. We would have to measure their light at different wavelengths and this is not yet possible, but I imagine that this is what will happen in the future with large space telescopes,” he says.
No need to change model
“Our work that we have published offers new information in favor of an explanation that does not require drastic changes in the cosmological model,” Spanish astrophysicist Pablo Arrabal Haro, co-author of the article, explains to elDiario.es. “For more than a year now, the consensus among those of us who are dedicated to it is that the overabundance of bright galaxies in the early universe is due to the fact that several physical phenomena were different at that time in the universe, but it does not require a different cosmological model.”
The glut of bright galaxies is due to several different physical phenomena at that time in the universe, but it does not require a different cosmological model.
Pablo Arrabal Haro
— Astrophysicist and co-author of the article.
For the specialist, the initial idea that the cosmological paradigm needed to be changed was a sensationalist exaggeration that quickly proved to be useless. “This result reveals some of the physical mechanisms that favor less massive galaxies being more luminous in the ancient times of the universe compared to more recent times,” he says. And although the problem of the overabundance of bright galaxies is still present, he admits, “we are already able to implement different physical effects that solve the problem, but now we have to verify which of these processes are actually at play in the first few hundred million years, and in what proportion. “This is where the main problem lies at the moment.”
