The James Webb Space Telescope (JWST) has found that many early galaxies in the universe are not as massive as previously believed, easing concerns about discrepancies between observed galaxy sizes and existing cosmological theories, NASA says.
A recent study led by astronomer Katherine Chworowsky at the University of Texas at Austin is easing concerns about a so-called “crisis in cosmology.” Initially sparked by the discoveries made with NASA’s JWST, this crisis suggested that some early galaxies in the universe were appearing much larger and more massive than current theories could explain.
When researchers first observed galaxies formed shortly after the Big Bang, they expected to find small, young galaxies. Instead, they were shocked to see what looked like “Olympic bodybuilders”—galaxies that seemed to have grown impressively large in a short time. This led to concerns that our understanding of the universe, known as the standard model of cosmology, might need reevaluation.
New Findings
However, Chworowsky’s study, published in the Astronomical Journal, reveals that many of these early galaxies are not as massive as they initially appeared. The brightness of these galaxies is largely attributed to black holes at their centers, which create immense light as they consume gas.
“We are still seeing more galaxies than predicted, although none of them are so massive that they ‘break’ the universe,” Chworowsky said.
This finding was supported by data from Webb’s Cosmic Evolution Early Release Science (CEERS) Survey, which is led by Professor Steven Finkelstein.
Understanding Brightness
According to the new research, the galaxies that appeared overly massive likely have supermassive black holes that rapidly consume surrounding gas. The friction produced by this fast-moving gas generates heat and bright light, making the galaxies seem larger than if their brightness came solely from stars. When researchers removed these exceptionally bright galaxies —coined “little red dots” due to their color and size — from their calculations, they found that the remaining galaxies fit well within the expectations set by the standard model.
“So, the bottom line is there is no crisis in terms of the standard model of cosmology. Any time you have a theory that has stood the test of time for so long, you have to have overwhelming evidence to really throw it out. And that’s simply not the case,” Finkelstein said.
Still More to Explore
While this recent study has resolved some of the main concerns, it has opened up another question: why are there still about twice as many massive galaxies in Webb’s early universe data compared to predictions? One theory suggests that stars formed more rapidly back then than they do today.
“Maybe in the early universe, galaxies were better at turning gas into stars,” Chworowsky said.
In the star formation process, hot gas cools and collapses under gravity, forming stars. However, this process can be slow due to internal pressure caused by heating gas. Some scientists propose that the density of the early universe may have created conditions that allowed stars to form more quickly.
Evidence of Black Holes Continues
In addition to these findings, astronomers are studying the spectra of the “little red dots” discovered by Webb. Research teams, including CEERS, have found signs of fast-moving hydrogen gas, which is a hint of black hole accretion disks. This suggests that much of the light from these compact objects originates from gas swirling around black holes rather than from stars, further supporting the conclusion that these galaxies may not be as massive as initially thought.
More observations are planned to help clarify the contributions of light from stars versus that from the gas near black holes. As research continues, scientists are hopeful that they will gain a deeper understanding of these fascinating early galaxies.
The James Webb Space Telescope is the leading space science observatory in the world, dedicated to uncovering the mysteries of our solar system while also exploring distant worlds around other stars. It delves into the intricate structures and origins of the universe, helping to enhance our understanding of our place within it. This groundbreaking program is an international collaboration led by NASA, the European Space Agency and the Canadian Space Agency.
