Harvard astronomers are proposing a new theory that the mysterious “little red dots” first spied by the James Webb Space Telescope two years ago represent new galaxies forming inside spinning dark matter halos, placing the puzzling objects as essential elements of galactic evolution.
Since astronomers first spotted little red dots two years ago, they have proposed various explanations for the small, faint objects from the edge of the universe whose light is so distant that it only reaches us now from billions of years in the ancient past. Some of those suggestions have included the possibilities of massive black holes and densely packed galaxies.
Cosmic Time Machines
“Telescopes are time machines,” said lead author Fabio Pacucci, a Clay Fellow in the Harvard-Smithsonian Center for Astrophysics. “If you look at the moon, you see it as it was one second ago, and if you look at the sun, as it was eight minutes ago. If you look at these little red dots, it was billions of years ago.”
The James Webb Space Telescope was designed to be one of these “time machines,” with studying the “cosmic dawn” as a primary objective. That is the universal epoch following the Big Bang, which saw the birth of the first stars and black holes. Since its launch in 2021, James Webb has journeyed a million miles from Earth, where it orbits our Sun, looking off into the edges of time and space. So far, it has spotted hundreds of the little red dots.
Little Red Dots
As light travels across billions of light-years, the pull of the universal expansion widens the light’s wavelengths, causing a redshift, which combines with intervening dust to create the little red dots’ unique coloration. At some point, following their formation 600 million years after the Big Bang, the dots vanished, only being present in the most ancient light. Their combination of brilliance and small size either suggests the presence of a black hole or an incredible density of tightly packed stars.
“They are like cosmic fireworks,” said Pacucci. “They magically appear, and they are very visible for about 1 billion years. Then they just disappear.”
The researchers produced a new model, which indicated that the little red dots are not a unique type of galaxy, but the slowest spinning one percent of galaxies, existing inside of dark matter halos. This would suggest that our present means of observation are creating the anomaly, not that the little red dots are particularly unusual. With our current technological limitations, larger galaxies with a lower density and greater redshift may be invisible, leaving the most common examples of galaxies represented by little red dots as undetected.
A team of astronomers sifted through James Webb Space Telescope data from multiple surveys to compile one of the largest samples of “little red dots” to date (Image: NASA, ESA, CSA, STScI, Dale Kocevski (Colby College)).
Dark Matter Halos
“If you assume the little red dots are typically in the first percentile of the spin distribution of dark matter halos, then you explain all their observational properties,” said co-author Avi Loeb, the Frank B. Baird Jr. Professor of Science at Harvard.
“A dark matter halo is a cradle to form a galaxy,” said Pacucci. “The bigger the dark matter halo, the bigger the galaxy at the center.”
The new research places the little red dots as examples of dark matter halos. Astronomers suggest that halos made of mysterious dark matter may be important to galactic birth and evolution. As dark matter emits no light and is therefore invisible, these halos have not been directly observed; their existence is only extrapolated from data on the motion of objects in the cosmos and the bending of light.
“This potentially adds to our fundamental understanding of these objects,” leading little red dot researcher Dale Kocevski commented. “In addition, it provides a physical model that we can test going forward.”
“We are now debating what is the nature of a fundamentally new kind of galaxy that we’ve never seen before,” Pacucci said. “This will fundamentally change how we view the early evolution of the universe.”
The paper, “Cosmic Outliers: Low-spin Halos Explain the Abundance, Compactness, and Redshift Evolution of the Little Red Dots,” appeared in The Astrophysical Journal Letter on August 11, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.