New observations from the James Webb Space Telescope are transforming our understanding of the universe’s formative years, revealing that the first galaxies were turbulent, messy collections of gas and stars that struggled to achieve order. An extensive survey of more than 250 ancient galaxies has found that, unlike the serene, rotating spirals we see in the modern cosmos, most of their predecessors were chaotic, clumpy, and far from settled. These findings provide the most detailed picture yet of a critical period in cosmic history, charting the clumsy beginnings of galaxies as they slowly evolved from暴风骤雨般的 assemblages into the structured systems that populate the universe today.
This research, published in the Monthly Notices of the Royal Astronomical Society, offers a comprehensive look at a large population of galaxies as they existed between 800 million and 1.5 billion years after the Big Bang. By analyzing the internal movements of gas within these primordial systems, astronomers at the University of Cambridge have shown that the calm, ordered rotation seen in galaxies like our own Milky Way was a rarity in the early universe. Instead, the evidence points to a period dominated by gravitational instability and furious bursts of star formation that constantly churned the galactic contents, puffing up gas in all directions and preventing the emergence of stable, flattened disks. This work helps bridge a significant gap between the dawn of the first stars and a later era known as “cosmic noon,” when star formation reached its peak, illustrating the gradual, difficult transition from chaos to order.
A New Portrait of the Cosmic Dawn
The study provides an unprecedented census of galactic dynamics during a key transitional period of the universe. By focusing on a large and diverse sample of 250 galaxies, researchers were able to move beyond the limitations of earlier observations, which often targeted only the most massive and spectacular examples. This broader view revealed a wide spectrum of galactic states. While a few galaxies showed early signs of settling into organized rotation, the vast majority were still in a state of disarray. First author Lola Danhaive, from Cambridge’s Kavli Institute for Cosmology, noted the significance of observing the entire population at once. “We don’t just see a few spectacular outliers,” she stated. “We found huge variation: some galaxies are beginning to settle into ordered rotation, but most are still chaotic, with gas puffed up and moving in all directions.” This finding paints a picture of the early universe as a far more tumultuous and unsettled place than previously thought, where galaxies were actively struggling to establish the stable structures that would later become commonplace.
The Engine of Galactic Chaos
The turbulence observed in these nascent galaxies was not random but was driven by fundamental physical processes inherent to that era of cosmic evolution. The researchers identified two primary drivers behind the widespread disorder: the vast reservoirs of gas available to young galaxies and the intense star formation that this gas fueled.
Fueling a Star-Forming Firestorm
Early galaxies were immersed in a cosmos rich with hydrogen gas, the raw material for making stars. This abundance of fuel triggered immense bursts of star formation at rates far exceeding those in the modern universe. This rapid conversion of gas into stars was a violent process. The energy and radiation blasting from massive young stars, along with the explosive force of subsequent supernovae, injected huge amounts of energy back into the surrounding gas. This constant feedback acted like a powerful internal engine, stirring the galactic disk and preventing the gas from settling into a calm, orderly rotational pattern. The high gas content essentially made these young galaxies top-heavy and prone to disruption from within.
The Grip of Gravitational Instability
Beyond the turmoil caused by star formation, the sheer quantity of gas made these early galaxies gravitationally unstable. When a galactic disk contains a high proportion of gas relative to its stars, its own gravity can cause it to fragment into dense, clumpy regions. These clumps would then move chaotically, further disrupting any tendency toward smooth rotation. This internal gravitational unsteadiness, combined with the energetic feedback from star birth, created a sustained state of turbulence that defined the character of most galaxies in this epoch. The galaxies were effectively engaged in a constant battle with their own star-forming frenzy and gravitational self-destruction, a phase they had to overcome to evolve into the stable systems seen today.
A Novel Technique in Telescopy
To measure the subtle movements of gas in galaxies billions of light-years away, the research team leveraged a specialized capability of the James Webb Space Telescope. This required not only a unique instrumental setup but also the development of new software to interpret the complex data.
Webb’s Powerful Grism Mode
The astronomers used the telescope’s Near Infrared Camera (NIRCam) in a configuration known as “grism mode.” This technique combines imaging with spectroscopy, allowing the instrument to capture the faint light emitted by ionized hydrogen gas. By analyzing the slight shifts in the wavelength of this light—a phenomenon known as the Doppler effect—the team could create detailed maps of how the gas was moving inside each of the 250 distant galaxies. This powerful method provided a direct window into the internal dynamics, or kinematics, of these systems, revealing whether the gas was rotating smoothly or moving in a more disordered fashion.
Decoding a Flood of Data
The grism mode, while powerful, produces complex data that is challenging to analyze. To overcome this, Danhaive developed new code specifically designed to process the faint signals from these early galaxies. By matching the grism data with other deep-field images captured by Webb, the team could precisely measure the velocity and direction of gas flow across each galaxy. This innovative approach was crucial for turning the raw telescope observations into the clear kinematic maps that underpinned the study’s conclusions about the chaotic nature of these systems.
Re-evaluating Galactic Growth Models
The new findings challenge some earlier interpretations of galaxy formation that were based on smaller, more selective samples. Prior results had hinted that massive, well-ordered disk galaxies could form very early in cosmic history, a scenario that did not align well with many theoretical models of gradual assembly. Dr. Sandro Tacchella, a co-author from the Kavli Institute, explained the importance of the new, larger survey. “Previous results suggested massive, well-ordered disks forming very early on, which didn’t fit our models,” he said. “But by looking at hundreds of galaxies with lower stellar masses instead of just one or two, we see the bigger picture, and it’s much more in line with theory.” The research suggests that the path to order was a marathon, not a sprint, with galaxies requiring billions of years to tame their internal turbulence and settle into the stable spiral structures that are common in the local universe.
Bridging Key Cosmic Eras
This comprehensive study does more than just characterize a single moment in time; it helps connect two of the most critical phases in the evolution of the cosmos. It provides a crucial link between the very early universe and the period when galaxies were at their most productive.
From the First Light to Cosmic Noon
The galaxies observed in this study existed at the tail end of the “epoch of reionization,” when the first stars and galaxies lit up the universe, and just before “cosmic noon,” the period about 2 to 3 billion years after the Big Bang when star formation activity across the universe peaked. “This work helps bridge the gap between the epoch of reionization and the so-called cosmic noon,” Danhaive commented. It reveals the crucial intermediate step where the “building blocks of galaxies gradually transitioned from chaotic clumps into ordered structures.” This provides a clearer timeline of how the universe matured, moving from its simple initial state to one filled with complex, structured galaxies.
The Long Road to the Milky Way
Ultimately, the turbulent systems revealed by Webb are the direct ancestors of mature galaxies like our own Milky Way. The chaotic, gas-rich clumps observed by the telescope eventually merged, stabilized, and consumed their fuel, allowing ordered disks to finally emerge. As the free-floating gas was gradually locked up in stars over billions of years, the primary sources of turbulence diminished, and gravity could finally shape the galaxies into the elegant spirals seen today. This research provides a foundational view of the starting point for that long evolutionary journey, showing that even the most majestic modern galaxies had messy and difficult childhoods.
