Greenbelt, Maryland — NASA’s James Webb Space Telescope is revolutionizing our comprehension of the cosmos by delivering extraordinary insights into the origins and structures of faraway galaxies. Recent research from the Webb team has uncovered pivotal information regarding the development of disk galaxies, including our own Milky Way.
Disk galaxies, which bear a distinctive disk-like formation, generally feature a prominent outer disk thick with stars and a thinner inner disk. With Webb’s capability to examine galaxies that existed up to 11 billion years ago, astronomers are poised to gain a clearer picture of how these intricate formations came into being.
The current configuration of disk galaxies, like the Milky Way, consists of two primary structures: a robust outer disk and a more delicate inner disk. The Milky Way’s thick disk extends roughly 3,000 light-years from its core, while the thinner disk measures about 1,000 light-years in thickness. For years, scientists have grappled with the enigma of how and why these dual structures developed. By meticulously analyzing Webb’s data, researchers are beginning to outline the timeline and processes responsible for the formation of these galactic structures.
Focusing on 111 edge-on disk galaxies, a study reveals how these cosmic entities evolved since roughly 2.8 billion years after the Big Bang. This marks a groundbreaking achievement, as it represents the first instance where scientists can effectively distinguish between thick and thin disk components across such vast distances. According to Takafumi Tsukui, the lead author, Webb’s unparalleled resolution has enabled astronomers to measure and differentiate between these structures, which were previously deemed indistinguishable.
A significant finding from this research is that thick disks emerge before their thinner counterparts. The timing of this formation appears to hinge on the mass of the galaxy. For example, more massive galaxies transitioned to the dual-disk structure around 8 billion years ago, while their less massive counterparts began forming thinner disks only about 4 billion years ago.
To understand the timing differences, the team examined gas dynamics within these galaxies. Utilizing data from the Atacama Large Millimeter/submillimeter Array (ALMA) and various ground-based surveys, they found that the evolution aligns with the “turbulent gas disk” hypothesis. This concept posits that early galaxies were enriched with turbulent gas, which sparked vigorous star formation and led to the creation of a thick stellar disk. As star formation progressed, it stabilized the gas, allowing the disk to settle down and gradually thin out.
The transition from a singular, thick disk to a dual-disk anatomy is a slow, continuous process. The thick disk continues to grow as the galaxy evolves, but at a pace that lags behind the thinner disk.
Webb’s advanced sensitivity has proven transformative in the study of distant galaxies. Its exceptional capabilities allow researchers to investigate smaller and fainter galaxies resembling the Milky Way from earlier epochs of cosmic history. This extraordinary sensitivity was crucial in pinpointing the formation timelines of disk structures in galaxies located up to 11 billion light-years away.
For the first time, astronomers successfully resolved thin stellar disks at such high redshifts, revealing that these structures may have begun to form as early as 8 billion years ago. Emily Wisnioski, a co-author of the study, remarked on the unexpected nature of this finding, highlighting how surprising it was to discover that thin disks existed so long ago.
As the James Webb Space Telescope continues its mission, the astronomical community eagerly anticipates further revelations from its observations, with implications that could redefine our understanding of galaxy formation and the early universe.