Galaxies have traditionally been viewed as evolving from their centers, with star formation concentrated in their cores and expanding outwards over time. However, this newly discovered galaxy, situated over 12 billion light-years away, has challenged this notion by showing active star formation on its outer edges, leaving an aging, inactive core.
The Early Universe and Star Formation
The prevailing model of galaxy formation suggests that galaxies evolve by pulling intergalactic gas into their cores, leading to the birth of new stars. This gravitational pull is most concentrated in the core of a galaxy, making it a prime location for star formation. As the gas is consumed, star formation spreads outwards, causing galaxies to grow in size and complexity over time. However, this recent discovery, made possible by the James Webb Space Telescope (JWST), offers a contrary perspective—one where the most intense star formation happens not in the center, but at the galaxy’s edges.
Using the JWST’s advanced capabilities, astronomers were able to capture detailed spectra from this distant galaxy, revealing that the core is dominated by older stars that are slowly fading, while the outskirts are bustling with new star formation. This inside-out growth presents a new model of galaxy evolution, prompting questions about the role of gas inflow, the environment of the early universe, and how other galaxies might have followed similar paths.
The Role of the James Webb Space Telescope
The discovery would not have been possible without the JWST. Equipped with sensitive infrared instruments, the JWST can peer through cosmic dust and observe structures billions of light-years away, which was a limitation for older telescopes like Hubble. The JWST’s spectroscopic instruments provided astronomers with the ability to map the galaxy in different wavelengths, allowing them to calculate the age and distribution of stars across its structure.
This observational power revealed the surprising fact that the older, dimmer stars were clustered in the core, while new, hot stars were forming on the periphery of the galaxy. By identifying where star formation is taking place, the JWST has allowed researchers to challenge long-standing theories about how galaxies grow and evolve in the early universe.
The data obtained from the JWST’s observations offers a new framework for understanding the process of star formation. It suggests that early galaxies may not rely solely on mergers and collisions to grow. Instead, they might develop in isolation, drawing in gas from their surroundings to form stars in their outskirts, a process that was previously only speculated but never observed directly.
Challenging the Conventional Model
For decades, astronomers believed that galaxies primarily grew through a combination of mergers and star formation concentrated in their cores. This conventional model suggested that gas would be funneled into the center of a galaxy, triggering new star births, and causing the galaxy to expand outward. But the discovery of this inside-out galaxy questions whether this model applies to all galaxies, particularly those in the early universe.
The newly discovered galaxy, with its fast-growing edges, supports the idea that some galaxies might develop more organically—by pulling in gas from their surroundings and creating stars in less concentrated regions. This contradicts the earlier assumption that galaxy growth was always dominated by mergers, where two or more galaxies collide, leading to bursts of star formation.
One theory for this discrepancy is that, in the early universe, galaxies were surrounded by more intergalactic gas than previously thought. As these galaxies drew in gas from their outer regions, new stars formed further away from the galactic center. This process, though unexpected, might have been more common than originally believed, especially in the chaotic, gas-rich environments shortly after the Big Bang.
Implications for Galaxy Evolution
This discovery also has implications for the broader understanding of how galaxies like our own Milky Way evolved. Our galaxy is still forming new stars, but at a much slower rate, and mainly in its outskirts. This slow, outward growth contrasts with the rapid star formation seen in the early universe. Understanding how this process unfolded over billions of years can shed light on how different types of galaxies—spiral, elliptical, and irregular—came to dominate the universe.
The rapid star formation in the outskirts of this early galaxy suggests that galaxies in the early universe might have grown much faster than those we observe today. The observed galaxy, despite its small size, is doubling its mass every 10 million years, whereas the Milky Way, in contrast, takes billions of years to double in size. This faster growth rate aligns with cosmological simulations that suggest galaxies in the early universe experienced rapid phases of expansion.
However, this accelerated growth also raises new questions about the availability of intergalactic gas and how galaxies in the early universe accumulated this gas to sustain their rapid development. These findings could help astronomers refine their models of galaxy evolution, particularly in the early stages of the universe’s history.
Inside-Out Growth and the Role of Dark Matter
One of the key factors in understanding galaxy growth is the role that dark matter plays in shaping the structure of galaxies. Dark matter, though invisible and undetectable through conventional means, is thought to make up the majority of the universe’s mass and to provide the gravitational framework that holds galaxies together.
In the case of this inside-out galaxy, the way gas is being drawn in from the galaxy’s outskirts might provide new insights into how dark matter interacts with visible matter. The distribution of stars and gas in this galaxy suggests that dark matter may play a crucial role in supporting the galaxy’s structure and driving star formation away from the core.
Further study of how dark matter influences the flow of gas and the formation of stars in early galaxies will be essential for building more accurate models of galaxy evolution. This galaxy could serve as a case study for understanding the interplay between dark matter, gas, and star formation across cosmic time.
A Broader Context: What We Learn About the Universe’s Past
This discovery offers astronomers a new piece of the puzzle in understanding how galaxies formed and evolved in the universe’s earliest epochs. It challenges the idea that galaxy mergers were the dominant force driving growth in the early universe, offering an alternative pathway where galaxies can grow by accumulating gas and forming stars on their outskirts.
In addition to providing a fresh perspective on galaxy formation, the inside-out growth model could help astronomers refine their understanding of the universe’s large-scale structure. By studying galaxies like this one, astronomers can develop better models for how galaxies cluster together in groups and superclusters, and how these structures have changed over time.
The Future of Cosmic Discovery
As we move forward, the JWST and other next-generation telescopes will continue to push the boundaries of our knowledge. This discovery represents just the beginning of what the JWST is capable of, and as more distant galaxies are observed in similar detail, we may find that inside-out growth is a more common phenomenon than previously thought.
Future research will likely focus on finding more examples of galaxies with this growth pattern to determine whether this was an unusual occurrence or a widespread feature of galaxy evolution in the early universe. If the latter proves true, we may need to revise our models of galaxy formation and consider new mechanisms that govern the development of galaxies over cosmic time.
Conclusion: A New Understanding of Star Formation
The discovery of a galaxy growing from the outside in offers a new chapter in our understanding of how galaxies evolve. While the conventional model of star formation focused on growth from the core outward, this inside-out galaxy suggests that the early universe may have been more diverse in its processes than previously believed.
The implications for this discovery extend far beyond one galaxy. It could reshape how we understand the development of galaxies, the role of dark matter, and the evolution of the universe itself. With the JWST continuing to provide groundbreaking data, we are likely to see even more surprising discoveries in the coming years, each one adding to our understanding of the cosmos.
Reference:Baker, W.M., Tacchella, S., Johnson, B.D. et al. A core in a star-forming disc as evidence of inside-out growth in the early Universe. Nat Astron (2024).
