James Webb Space Telescope Reveals Milky Way's Evolution Through Cosmic Archeology

In a groundbreaking study, astronomers have utilized the James Webb Space Telescope (JWST) to investigate ancient disk galaxies, providing new insights into the evolutionary history of the Milky Way galaxy and its counterparts. This research, published in the July 2025 edition of the Monthly Notices of the Royal Astronomical Society, uncovers the structures of galaxies that existed up to 11 billion years ago, shedding light on the formation of thick and thin stellar disks and the processes that underpin these formations.

The investigation centered on the analysis of 111 edge-on disk galaxies, which allowed researchers to categorize them into dual-disked and single-disked galaxies. Lead researcher Takafumi Tsukui, an astronomer at the Australian National University, emphasized that this study represents a significant advancement in understanding the timing and conditions under which these disks developed. According to Tsukui, "This unique measurement of the thickness of the disks at high redshift is a benchmark for theoretical study that was only possible with the JWST." The data revealed that high-mass galaxies transitioned to dual-disk structures approximately 8 billion years ago, while their lower-mass counterparts did so around 4 billion years ago.

The JWST's advanced capabilities, including its resolution and ability to penetrate cosmic dust, enabled scientists to distinguish between the two types of stellar disks. Emily Wisnioski, a researcher also at the Australian National University, noted, "To see thin stellar disks already in place 8 billion years ago, or even earlier, was surprising." This discovery is pivotal as it correlates with theoretical models of how the Milky Way itself formed its thin disk.

The team further investigated the dynamics of gas around these galaxies, utilizing data from the Atacama Large Millimeter/submillimeter Array (ALMA) and other observatories. The analysis indicated that turbulent gas in the early universe instigated bursts of intense star formation, leading to the creation of thick stellar disks. As these stars formed, the gas became more stable, allowing for the formation of thin stellar disks.

This dual-disk formation process varies between high-mass and low-mass galaxies due to differences in their star formation efficiencies. The findings contribute to a broader understanding of galactic evolution and provide a new perspective on the Milky Way's formative years.

The implications of this research extend beyond our galaxy. By examining these ancient galaxies, astronomers are not only piecing together the history of the Milky Way but also gaining insights that may apply to other galaxies throughout the universe. Tsukui and his team aim to enhance their study by incorporating additional data on stellar motion, age, and metallicity, which could further refine our understanding of galaxy formation.

In conclusion, the JWST's role as a cosmic archeologist has opened new avenues for exploring the history of the universe. As the research progresses, it promises to bridge the gap between our understanding of nearby galaxies and those from the early universe, revealing the intricate processes that have shaped the cosmos over billions of years.