Recent observations from the James Webb Space Telescope (JWST) have revealed that the universe’s first galaxies were far from the neatly organized structures we see today. Instead, these early galaxies were turbulent, chaotic bundles of gas, undergoing periods of intense star formation, and influenced by rapidly growing supermassive black holes. This paints a vivid picture of a “messy era” in cosmic history.
Observing Galaxies at Cosmic Dawn
A team of astronomers, led by Lola Dunhaive of Cambridge University, used the JWST’s NIRCam instrument to study 272 small galaxies, dating back 800 million to 1.5 billion years after the Big Bang. Light from these distant galaxies has taken billions of years to reach us, providing a unique window into the universe’s early stages – a period known as Cosmic Dawn (50 million to 1 billion years after the Big Bang) that preceded Cosmic Noon (2 to 3 billion years after the Big Bang), when star formation reached its peak.
The Turbulent Nature of Early Galaxies
The observations showed that, unlike the smoothly rotating disks of gas and stars prevalent in nearby galaxies, gas movement in these early galaxies was turbulent. Instead of circling their centers in ordered currents, gas flowed in multiple directions, creating chaotic eddies, shock waves, and uneven clumps of matter. The team described these early galaxies as being “at the dawn of disks”, going through multiple phases of instability before settling into the ordered structures we observe today.
Factors Contributing to the Chaos
Several factors contributed to this turbulent state:
- Rapid Star Formation: Newborn stars, like newborn humans, can be erratic. These young stars emitted powerful stellar winds and blasts of high-energy radiation, disrupting the surrounding gas clouds where they formed.
- Denser Intergalactic Gas: Because the universe has been expanding since the Big Bang, it was a smaller, denser place just before Cosmic Noon. This meant more intergalactic gas flowed into early galaxies, further fueling turbulence.
- Supermassive Black Holes: The supermassive black holes at the centers of these galaxies were actively feeding on gas, expelling matter and radiation, and contributing to the chaotic environment.
- Smaller Size: Compared to galaxies in the present-day universe, these early galaxies were relatively small (ranging from 100 million to 10 billion times the mass of our sun), meaning that events like bursts of star formation and the activity of black holes had a proportionally larger impact on their stability.
Exceptions and Future Research
While most galaxies in the study exhibited turbulent behavior, a few showed signs of earlier stability, tending to be larger and perhaps more resilient. These observations largely confirm predictions from existing models of galactic evolution, solidifying the link between observation and theory.
Dunhaive and her colleagues plan to combine their observations of ionized hydrogen gas with upcoming observations of cold gas and dust, allowing for a more comprehensive understanding of the structure and evolution of these early galaxies. “With more data, we’ll be able to track how these turbulent systems grew up and became the graceful spirals we see today,” explains Sandro Tacchella, a coauthor of the study. The new data will reveal more about the structures and evolutionary paths of these ancient, formative galaxies.
The study offers a valuable insight into the dynamic and often chaotic conditions that characterized the early universe, and underscores the critical role that the JWST plays in unraveling the mysteries of cosmic evolution.
