Simulations suggest JWST’s Little Red Dots are rapidly growing early-Universe black holes

Sunmyon Chon of the Max Planck Institute for Astrophysics and colleagues used the ATERUI III supercomputer to run simulations showing that the James Webb Space Telescope’s puzzling Little Red Dots are rapidly growing black holes from the early Universe, published in Nature in 2026. The findings address how supermassive black holes with millions or billions of solar masses could exist less than 600 million years after the Big Bang. Observing distant galaxies means looking into the past, since light travels at a finite speed.

The simulations reveal a natural pathway to these enormous black holes. Intense far-ultraviolet radiation from nearby galaxies can prevent star formation inside some gas clouds. Gas blocked from star formation collapses into a single supermassive star, which then collapses to create a black hole seed, and once these seeds form, thick disks of dense gas surround them, trapping radiation and enabling efficient material consumption. Under these conditions, black holes can grow dozens of times faster than would be possible today, according to the model.

The research began simulations on the scale of a young galaxy and progressively focused on smaller regions until reaching individual clouds of gas. The conditions needed to create and rapidly grow black holes developed naturally in the early Universe without exotic assumptions or rare coincidences, according to the model. Co-authors included Shingo Hirano, Tomoaki Ishiyama, Seok-Jun Chang, and Volker Springel.

The James Webb Space Telescope revealed a population of red objects called Little Red Dots whose true nature had remained unclear. When JWST began science operations in July 2022, hundreds of these faint, blood-red objects appeared across deep-field images, prompting calculations that their abundance implied far more massive supermassive black holes than standard models predicted. The objects appeared roughly 600 million to 1.6 billion years after the Big Bang and then seemed to vanish from the more recent universe, a disappearance that once fueled speculation that cosmology was broken.

A paper published July 29, 2026, in The Astrophysical Journal provides a nearby analog. The key galaxy, nicknamed the Saguaro for its prominent arms, is a redshift-2 object roughly 10.4 billion light-years away, about 3.3 billion years after the Big Bang. It came to the team’s attention through archival JWST data. Pierluigi Rinaldi of the University of Arizona’s Steward Observatory led the finding.

JWST and the Hubble Space Telescope observed the full Saguaro spiral galaxy at high resolution, disentangling light from its extended disk, star-forming arms, and luminous core.

The Saguaro’s compact, intensely luminous red nucleus matches every known characteristic of a little red dot, exhibiting the defining V-shaped spectral profile that makes these objects brighter in ultraviolet and infrared light than in visible wavelengths. NASA’s Chandra X-ray Observatory detected faint X-ray emission from the Saguaro’s core, weak but present. Carys Gilbert, a Master’s student at the University of Cape Town and co-author of the paper, said the obscured and X-ray weak combination fits the puzzle of little red dots nicely.

The Rinaldi team’s work shows the disappearing little red dot population was never gone; too far for JWST to detect its context, leaving only the compact central dot bright enough to survive across 13 billion light-years. The team mathematically moved the Saguaro to simulate what JWST would detect if the galaxy sat at 13 billion light-years instead of 10.4 billion. The galaxy’s spiral arms, star-forming regions, and extended disk all disappeared below detection, leaving only the compact, intensely luminous red nucleus visible, indistinguishable from any of the 341 catalogued little red dots. At high redshifts, extended objects dim dramatically because their surface brightness scales with (1+z)^4 while point sources fade more slowly.

Other researchers have proposed different origins for these objects. An arXiv study posted November 5, 2024, described quasi-stars as massive envelopes around accreting black holes that formed when supermassive stars collapsed, and said the standard path to those stars needs strong Lyman-Werner backgrounds, sustained gas inflow, and rotational backing. The paper shows supermassive dark stars powered by dark matter annihilation satisfy key requirements while relaxing those restrictive conditions, and these dark stars are zero metallicity gas clouds powered by dark matter annihilation rather than nuclear burning, remaining cool while accreting at roughly 10^-2 solar masses per year and reaching roughly 10^6 solar masses. Quasi-stars formed through this pathway begin with prompt black hole masses of at least 10% of the progenitor mass, and their cool photospheres at roughly 3,000 to 6,000 kelvin can reproduce key features of many JWST Little Red Dots with luminosities of roughly 10^11 to 10^12 solar luminosities.

George Rieke of the University of Arizona said everything created in the early universe must evolve into something around us, and these results show how to find little red dot progeny. Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics described the Saguaro as a prototypical little red dot and one of the few found at lower redshift, usable to study their evolution through cosmic time. The researchers plan to search JWST’s archival data for intermediate-redshift galaxies with little red dot-like nuclei to build an environmental census. Not every little red dot follows the Saguaro’s example; the objects cover many luminosities, redshifts, and spectral traits, and some may form or end differently.