Original title: Bright star-forming galaxies naturally forming at z>10 in the Shark semi-analytic model
Claudia D. P. Lagos, Angel Chandro-Gomez, Chris Power, Aaron S. G. Robotham · September 2026
The James Webb Space Telescope spotted surprisingly bright ultraviolet galaxies in the very early universe, at redshifts greater than 10. These detections challenge current ideas of how galaxies form in a cold dark matter universe. To investigate this puzzle, researchers tested a computer model called Shark. They tuned this model only to match the local universe today. Without changing any of its physics or parameters, the model successfully matched real observations all the way back to redshift 17. It also matched how galaxy masses grew from redshift 0 to 10, plus cosmic star formation rates up to redshift 15. The secret lies in violent disk instabilitiesLarge-scale gravitational disturbances in a galaxy's disk that trigger intense star formation episodes., where chaotic disturbances inside rotating galaxies trigger sudden, massive bursts of star formation. Without these intense starbursts, the model galaxies are simply not bursty enough to recreate the bright early galaxies that telescopes see.
Imagine baking a cake with a recipe that's perfect for your sea-level kitchen. At high altitude, the lower air pressure changes how the cake rises, often causing it to fall flat. In this paper, the Shark model includes a mechanism for natural star formation bursts, which adjusts to the conditions at high redshift, so it predicts bright galaxies without altering its base physics.
JWST discovered unexpectedly bright galaxies from the early universe, which could strain our understanding. If a model based on local physics fits these observations, it reinforces the standard cosmological model.
The abstract does not state specific limitations, but it implies that the model reproduces current observational constraints reasonably well. It does not claim to solve all potential issues in galaxy formation theory.
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Bright star-forming galaxies naturally forming at z>10 in the Shark semi-analytic model — Claudia D. P. Lagos, Angel Chandro-Gomez, Chris Power et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.