admin When scientists saw the first images of the universe’s first galaxies taken by the James Webb Space Telescope (JWST), they were shocked. Young galaxies appear to be too bright, too massive, and too mature to have formed so soon after the Big Bang. It’s like a newborn baby will become an adult in just a few years.
This astonishing discovery even caused some physicists to question the standard model of cosmology, wondering whether it should be changed.
Thanks to new simulations, a team of astrophysicists led by Northwestern University has discovered that these galaxies may not be so big after all.Although a galaxy’s brightness is usually determined by its mass, new findings show that less massive galaxies can also shine brightly from bright, irregular bursts of star formation.
This discovery not only explains why young galaxies appear massive, but it also fits with the standard model of cosmology.
The study was published October 3 in the Astrophysical Journal. “The discovery of these galaxies was a big surprise because they are significantly brighter than expected,” said Claude-André Faucher-Giguère of Northwestern, lead author of the study.
“Normally, a galaxy is bright because it is large. But because these galaxies formed at the dawn of the universe, not enough time has passed since the Big Bang. How did galaxies Could this giant assemble so quickly? Our simulations show that Guochao Sun, who led the study, added: “The key is to reproduce enough light in a system in a short period of time”. “This can happen because the system is really big or because it has the ability to produce a lot of light quickly. In the second case, a system does not need to be that large. If star formation occurs in bursts, it would create Faucher-Giguère is an associate professor of physics and astronomy in the Weinberg College of Arts and Sciences at Northwestern and a member of the Discovery Center. and Interdisciplinary Research in Astrophysics (CIERA).Sun is a CIERA postdoctoral fellow at Northwestern.
A period of time lasting about 100 million to 1 billion years after the Big Bang, the cosmic dawn was marked by the formation of the first stars and galaxies in the universe. Before JWST was launched into space, astronomers knew very little about this ancient period.
“JWST has given us a lot of knowledge about the cosmic dawn,” Sun said. “Before JWST, most of our knowledge about the early universe was speculation based on data from very few sources. Thanks to greatly increased observational capabilities, we can see physical details about galaxies and use this powerful observational evidence to study physics and understand what is happening”.
In the new study, Sun, Faucher-Giguère and their team used advanced computer simulations to model the formation of galaxies immediately after the Big Bang. The simulations produced galaxies Galaxies at the dawn of the universe were brighter than those observed by JWST These simulations are part of the Feedback on Relativistic Environments (FIRE) project co-founded by Faucher-Giguère with collaborators at the California Institute of Technology, Princeton University, and the University of California at San Diego.
The new study includes collaborators from the Center for Computational Astrophysics at the Flatiron Institute, the Massachusetts Institute of Technology, and the University of California. California School, Davis.
FIRE simulations combine astrophysical theory and advanced algorithms to model galaxy formation. The models allow researchers to study how galaxies form, evolve and change shape, while also taking into account the energy, mass, momentum and chemistry that stars rotate through again.
When Sun, Faucher-Giguère and their team ran simulations to model the first galaxies formed at the dawn of the universe, they found that stars form in batches, a concept concept called “abundant star formation”. In giant galaxies like the Milky Way, stars form at a constant rate, their numbers increasing over time. But so-called explosive star formation occurs when stars form in an alternating pattern: many stars at once, followed by millions of years of very few new stars, then many new stars all at once.
“Bursty star formation is especially common in low-mass galaxies,” Faucher-Giguère said. “The details of why this happens are still the subject of ongoing research. But what we think happens is that a burst of stars form, then a few million years later, those stars explode as supernovae. The gas gets kicked out and then falls back in to form new stars, driving the cycle of star formation.”
“But when galaxies get massive enough, they have much stronger gravity. When supernovae explode, they are not strong enough to eject gas from the system. The gravity holds the galaxy together and brings it into a steady state.”
The simulations also were able to produce the same abundance of bright galaxies as the JWST revealed. In other words, the number of bright galaxies predicted by simulations matches the number of observed bright galaxies.
Although other astrophysicists have hypothesized that bursty star formation could be responsible for the unusual brightness of galaxies at cosmic dawn, the Northwestern researchers are the first to use detailed computer simulations to prove it is possible. And they were able to do so without adding new factors that are unaligned with our standard model of the universe.
“Most of the light in a galaxy comes from the most massive stars,” Faucher-Giguère said. “Because more massive stars burn at a higher speed, they are shorter lived. They rapidly use up their fuel in nuclear reactions. So, the brightness of a galaxy is more directly related to how many stars it has formed in the last few million years than the mass of the galaxy as a whole.”
