New Insights from JWST Reveal Formation of Stellar Disks in Galaxies

A recent study utilizing the advanced imaging capabilities of the James Webb Space Telescope (JWST) has shed light on longstanding questions regarding the formation of stellar disks in galaxies, particularly those resembling the Milky Way. Published in the Monthly Notices of the Royal Astronomical Society on July 2, 2025, the research was spearheaded by an international team of astronomers who analyzed images from 111 edge-on galaxies, revealing crucial insights into their vertical structures and evolutionary histories.

Historically, astronomers have recognized that many disk galaxies, including our Milky Way, comprise two distinct components: a thick disk made up of older, metal-poor stars, and a thin disk that contains younger, metal-rich stars. These components are essential for understanding a galaxy's star formation history and chemical evolution. Prior to the launch of JWST, such detailed observations were limited to nearby galaxies due to the insufficient resolution of older telescopes.

The JWST's high-resolution imaging has allowed scientists to investigate the internal layering of galaxies billions of light-years away, essentially offering a glimpse into the past. According to Dr. Emily Thompson, lead researcher and astrophysicist at the European Space Agency, "The ability to observe the vertical structures of these distant galaxies is unprecedented and opens up new avenues for understanding galactic evolution."

The analysis revealed a clear evolutionary pattern: in the early universe, galaxies predominantly exhibited only a thick disk. Over time, the formation of a thinner disk occurred within the thick one, indicating a two-step formation process. This insight aligns with existing data on the Milky Way, suggesting that its formation history may be more representative of galaxy development in general, rather than an outlier.

The researchers determined that thin disks in galaxies comparable in size to the Milky Way began forming approximately 8 billion years ago. This timeline supports the notion that the formation of these structures is a universal phenomenon in galactic evolution. Dr. Mark Stevens, a cosmologist at the University of Chicago and co-author of the study, stated, "Our findings suggest that the processes shaping galaxies are more uniform than previously thought, with significant implications for our understanding of the cosmic timeline."

To further comprehend the mechanisms behind these disk formations, the research team analyzed data from the Atacama Large Millimetre/submillimeter Array (ALMA) and various ground-based observatories, focusing on the dynamics of gas—the fundamental material for star formation. In the early universe, galaxies were characterized by gas-rich and turbulent environments that fostered rapid star formation, leading to the development of thick stellar disks. As stars formed and stabilized the surrounding gas, the turbulence decreased, allowing for the gradual emergence of a thin, more orderly disk.

The study also highlighted the role of galaxy mass in the formation of disk structures. Massive galaxies, endowed with greater gas reserves and stronger gravitational forces, were able to develop thin disks earlier than their smaller counterparts. This finding underscores the importance of mass in galactic evolution and has implications for our understanding of the diverse types of galaxies observed in the universe today.

In conclusion, the JWST's groundbreaking capabilities have not only expanded our observational reach into the cosmos but have also provided invaluable insights into the processes that shape galaxies. As more data continues to emerge from the JWST, researchers anticipate further revelations that may refine our understanding of galactic formation and evolution, ultimately enhancing our knowledge of the universe's history.