Tim Tai

Yale researchers co-authored the study uncovering “ultra-massive” galaxies formed briefly after the Big Bang, the creation of the universe.

The discovery was based on observations from the James Webb Space Telescope, or JWST, which began to orbit the sun in 2021 and was designed to gaze into the universe’s origins. These extremely large galaxies discovered by researchers challenge the existing understanding of galactic evolution.

“In our model for the formation of structure in the universe, galaxies start out small and gradually build up over many billions of years,” explained Pieter van Dokkum, professor of astronomy and physics and the paper’s co-author. “Seeing these ‘monster’ galaxies early in the history of the universe doesn’t fit very nicely with this model.”

These “ultra-massive” galaxies are also referred to as “monster galaxies” due to their size and rapid star formation. Instead of seeing smaller, low-mass galaxies that grow, researchers observed massive galaxies, some larger than the Milky Way, that formed early.

Researchers identified the galaxies’ startling sizes by detecting their light emissions with the JWST. There are often two ways to determine the size of a galaxy — from the stars’ light emissions or by material caught in the spiral of a massive black hole. 

Dokkum explained that identifying the cause of this light can be difficult, especially within early galaxies like the ones found in the study. 

“We see something that’s very bright, but we don’t know if it’s because there are a lot of stars there or because there is a big black hole there,” Dokkum said. However, “for these three galaxies, we see that the light is spread out. That means it’s not all coming from a single point, which is what we would have if the light came from material falling into a black hole.”

Observations of such “monster” galaxies continue to raise new questions for researchers at Yale. 

Josephine Baggen GRD ’28, a researcher in van Dokkum’s Group studying high-redshift galaxies detected with JWST data, is trying to understand how the current model can accommodate these unexpected phases of galaxy formation.

“This does not mean the model is wrong, it is just likely missing some growth mechanisms at the early phases of galaxy formation,” Baggen said.

To accommodate for the discovery, Baggen explained, the paper calls for some “accelerated growth phase” in the early universe, rapid growth phases that created the “monster galaxies” observed in the study.

These new findings add to the understanding of galaxy formation and it presents a more efficient method scientists hope to explore further. At Yale, Dokkum’s lab continues to study early massive galaxies like these using JWST data.

For Camille Chiu ’26, an astrophysics major who studies the chemical and dynamical properties of galaxies, these results could not be more fascinating.

“The findings are an important step forward in our understanding of how the first galaxies formed and are a testament to the unique and powerful capabilities of JWST in probing the early Universe. This kind of research would not have even been possible five years ago,” Chiu wrote to the News. “It is motivating to witness both the rapid pace of discovery and the emergence of so many new, unanswered questions.”

The Milky Way is roughly 100,000 light-years in diameter.