Key Takeaways:

  1. The James Webb Space Telescope’s observations suggest that early galaxies were more mature and numerous than previously believed, challenging existing notions of galaxy formation.
  2. Webb’s enhanced capabilities, including sharper images and greater sensitivity to longer wavelengths, have enabled the identification of 850 early galaxies, shedding light on their shapes and distributions.
  3. Despite their youth, early galaxies exhibit shapes similar to those nearer to us, with the prevalence of disk galaxies remaining relatively constant over cosmic time.
  4. Findings from the CEERS collaboration and other research teams highlight the need for computational methods to aid in the classification of galaxies, as well as the ongoing role of human analysis in scientific research.
  5. The discovery of a significant number of distant galaxies challenges previous models of galaxy formation, prompting re-evaluation of factors such as stellar feedback and the influence of dark matter halos in shaping early galactic structures.

The James Webb Space Telescope, as it surveys vast expanses of the sky adorned with remote galaxies, has led various research teams to make a remarkable discovery: the earliest galactic communities appear to be more developed and numerous than previously assumed. These findings hold the potential to reshape our understanding of the mechanisms behind the formation of the first galaxies.

This image — a mosaic of 690 individual frames taken with Webb’s Near Infrared Camera (NIRCam) — covers a patch of sky near the handle of the Big Dipper. This is one of the first images obtained by the Cosmic Evolution Early Release Science Survey (CEERS) collaboration and contains several examples of high-redshift galaxies with various morphologies, including a surprisingly high fraction of disks. NASA / STScI / CEERS / TACC / S. Finkelstein /M. Bagley / Z. Levay; Cutout images: NASA / STScI / CEERS / TACC / S. Finkelstein / M. Bagley / J. Kartaltepe

As a contributor to the Cosmic Evolution Early Release Science (CEERS) collaboration, Jeyhan Kartaltepe from the Rochester Institute of Technology shared insights into Webb’s observations of galaxies dating back to when the universe was between 500 million and 2 billion years old.

Earlier studies, including those conducted using the Hubble Space Telescope, suggested that as we peer back into the universe’s younger epochs, the orderly, rotating disks seen in contemporary galaxies give way to more chaotic configurations, indicative of the tumultuous mergers that assembled the earliest galaxies. However, previous studies struggled to classify the most distant galaxies, which often appeared as little more than faint smudges. This is where the Webb telescope proves invaluable.

With its ability to detect longer wavelengths, Webb can peer further back in time. Additionally, its images boast greater sharpness and sensitivity compared to those captured by Hubble. Leveraging these advancements, the CEERS team has identified 850 early galaxies, determined their distances, and categorized their shapes as either “disk,” “spheroid,” or “irregular.”

These classifications are not rigidly defined. “Galaxies are intricate and defy simple categorization,” explains Kartaltepe. Some galaxies exhibit characteristics of both a disk and a central bulge, reminiscent of our own Milky Way.

While future classification efforts may rely more on computational methods, such as convolutional neural networks, currently the task remains predominantly human. Three CEERS team members meticulously examined each of the 850 galaxies to assign classifications.

Remarkably, despite their youth, these galaxies bear resemblance to those closer to us. The prevalence of disk galaxies in the early universe only marginally declined, while the proportions of galaxies with a central bulge and those with irregular shapes remained relatively stable over cosmic epochs.

The presence of disk galaxies in an early universe, where serene conditions conducive to disk formation were presumed scarce, is akin to encountering adolescents when expecting toddlers, Kartaltepe remarks. “The existence of disk galaxies isn’t surprising per se,” she clarifies. “What’s astonishing is their abundance. . . . We have yet to witness the nascent stages of galaxy formation.”

A montage of JWST images shows barred galaxies dating back to between 8.4 billion and 11 billion years ago. Though not part of the current study, these barred galaxies are demonstrative of the mature galaxy shapes already present at early times. NASA/CEERS/University of Texas at Austin

Nevertheless, Kartaltepe notes that these early disks differ from their modern counterparts. “They’re not akin to today’s Milky Way,” she points out. “They’re turbulent, disorderly, and warrant further investigation.”

AN EXCESS OF DISTANT GALAXIES

During the same AAS press conference, Haojing Yan from the University of Missouri presented findings on galaxies even earlier in cosmic history. Utilizing Webb’s multi-wavelength images, Yan identified 87 distant galaxies located behind the galaxy cluster SMACS 0723, their light magnified and distorted by the cluster’s gravitational lensing. These galaxies are estimated to originate between 200 million and 400 million years after the Big Bang (corresponding to a redshift as high as 20).

Though these candidates await spectroscopic confirmation, preliminary estimates suggest that the vast majority of previously confirmed distances align with spectroscopic findings. Even if only half of Yan’s selection ultimately prove to be genuinely distant galaxies, the sheer number would still exceed expectations. “Our prior understanding of galaxy formation in the early universe requires reassessment,” Yan asserts.

Addressing this conundrum is theorist Jordan Mirocha from the Jet Propulsion Laboratory, who presented later during the conference. “Either there’s an overabundance of galaxies, or they’re significantly brighter than our conventional models predict,” Mirocha posits. He contends that various interrelated factors are at play, disrupting predictive models.

The earliest galaxies emerged within expanding dark matter halos, with ordinary hydrogen gas gravitationally drawn towards accumulating dark matter particles. Mirocha suggests that this influx of matter may have impeded the stellar feedback mechanisms that regulate star formation in contemporary galaxies. While the rapid formation of new stars would imbue early galaxies with luminosity, it would also generate dust, obscuring their brilliance.

Harmonizing these disparate factors is crucial for comprehending the genesis of the first galaxies. Mirocha understates the challenge: “I believe we have much to ponder.”

 

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