NASA’s James Webb Space Telescope has captured images of massive, bright, disky galaxies from the early universe that have surprised astronomers. These galaxies lived 11-12 billion years ago, just a few billion years after the Big Bang, but appear much more structured and developed than models predicted for galaxies at that age.
Disky Structures Unlike Predictions
Scientists expected early galaxies to be small, chaotic, and bursting with star formation. But the galaxies spotted by Webb show grand spiraling disk structures stretching across 60,000 lightyears or more – two or three times wider than our Milky Way galaxy today.
“Their disk-like appearance is more organized than astronomers expected,” said astronomer Erica Nelson of the University of Colorado. “These galaxies are dynamically mature at an unexpectedly early epoch. Galaxies at this time were still supposed to be building themselves up, accreting gas, and forming new stars throughout the entire galaxy, not just the core.”
Bright Center Regions Still a Mystery
These massive disky galaxies also have extremely bright central regions, suggesting they host active supermassive black holes at their cores. But theoretical models do not predict mature supermassive black holes existing this early on.
“Our predictions could be incomplete. We thought disks and black holes came later in the life cycle of galaxies,” Nelson said. “These JWST images challenge all of the textbook cartoons predicting chaotic and clumpy galaxies early on.” Resolving this mystery about the inner structure, mass, and luminosity of these early galaxies will be a key goal for Webb scientists in coming years.
Implications for Models of Galaxy Formation
The existence of these surprisingly structured early galaxies requires rethinking models for how galaxies assemble themselves. Richmond University astronomer Rebecca Larson said, “Seeing developed disk galaxies this early means galaxy maturation must happen earlier and faster than our theories predicted. These galaxies will force us to revise our basic assumptions.”
There are multiple theories about what could explain these precocious galaxies. Some possibilities include:
- Very rapid bursts of star formation early on
- Earlier start to supermassive black hole growth
- Different distributions of dark matter influencing gas cloud collapse
- Faster accretion of gas into denser disks due to environment
“Any explanation must allow galaxies to reach this level of maturity and organization much sooner after the Big Bang,” Larson said.
|Intense bursts of star formation could rapidly fuse gas clouds into disks
|Early black holes
|Unpredicted fast growth of central black holes
|Dark matter differences
|Subtle dark matter changes influencing gas disk shapes
|Environmental gas flows
|More rapid flows of gas into disks based on location
Webb Program Director: Findings Will “Transform Cosmology”
Dr. Amber Straughn, Astrophysics Division Director for the Webb telescope, said these surprising observations are exactly why NASA built Webb – to discover the unexpected and transform our view of the cosmos.
“These early massive disk galaxies will force us to revise models of galaxy assembly. Webb’s finds have shattered many assumptions about the early universe. We expected chaos, not order. The textbooks will need rewriting,” Straughn said at a press conference revealing the results.
“This is just the start of Webb’s exploration,” she added. “We will soon study these galaxies in more detail and discover many more surprises about the early cosmos. Webb is poised to transform cosmology in ways we never imagined.”
What’s Next: More Observations Over Coming Year
The disky galaxies were spotted in just Webb’s first deep field image. Researchers have already booked extensive Webb observation time over the next year to analyze these galaxies in more detail and find more early universe galaxies.
Goals for follow-up study include:
- Precisely dating galactic chemical compositions to confirm ages
- Learning more about star formation rates and conditions
- Charting exactly how common these massive disk galaxies were
- Using gravitational lensing to map dark matter structure
- Finding more examples to increase study sample size
- Connecting galactic features to theories about fast formation
A key open question is exactly how rare or common these galaxies were at that time. If very rare, they may have been an unusual pocket of precocious development. If more common, then theories predicting slower galaxy evolution are seriously incomplete. Resolving this will require finding and studying more examples researchers said.
Within a year, Webb scientists hope to have a much clearer picture of massive galaxy development near cosmic dawn. Until then, textbooks about the early universe will need major revisions amidst the surfboard-shaped surprises spotted by the Webb telescope.
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