Since it began operations, JWST has identified distant galaxies that seem to host surprisingly large populations of ancient black holes. Astronomers have dubbed these anomalous galaxies little red dots because they appear this way in the telescope’s highly sensitive instruments. The timeline of these compact objects challenges established views of cosmic evolution. Priyamvada Natarajan, a theoretical astrophysicist at Yale University, notes that these observations far exceed theoretical predictions. “James Webb is discovering many more black holes than most of us theorists predicted in our most optimistic models,” says Natarajan. “The universe is just littered with black holes.”
The Problem with Early Universe Black Holes
In standard cosmological models, black holes typically form when massive stars exhaust their nuclear fuel and collapse. However, finding these objects so early in the universe’s history means there was not enough time for sufficiently massive stars to form, live, and die. To explain this discrepancy, scientists previously turned to the concept of primordial black holes. These black holes theoretically formed in violent space-time spasms immediately following the Big Bang, before any stars existed.
However, this violent formation process conflicts with the milder ripples astronomers observe in the cosmic microwave background (CMB). The CMB is faint light left over from the primordial universe, representing radiation released roughly 380,000 years after the Big Bang. It contains tiny temperature fluctuations that reflect the distribution of matter. To make violent primordial black hole theories align with these gentle CMB fluctuations, theorists had to propose complicated, unproven new laws of physics to artificially enhance early universe density perturbations.
Dark Matter Seeds and the Cosmic Microwave Background
Wenzer Qin and Neal Weiner at New York University, alongside Soubhik Kumar at Tufts University, realized there was another mechanism that requires no invented physics. They began by assuming milder ripples of this invisible matter moved through the early universe. They argued that large primordial black holes would be able to form inside these dense clumps.
Crucially, the intensely hot CMB at that time acted as a filter. The radiation would keep ordinary matter—gas and dust—hot enough to prevent it from collapsing into smaller black holes. Meanwhile, the invisible mass could clump quietly, providing the necessary gravitational wells for large primordial black holes to form directly. The researchers call these objects “not-quite-primordial” black holes because they form before stars but rely on dark matter rather than violent space-time spasms.
This distinction is vital. Traditional models required extreme density unevenness, which would leave visible scars in the CMB. By shifting the heavy lifting to a substance that does not interact with light directly, the researchers elegantly bypass the CMB constraints. They argue this process provides a viable explanation for the JWST discovery of black holes without requiring drastic changes to cosmologists’ existing picture of the early universe.
Validating the Primordial Black Holes Model
To ensure their logic held up, Qin and his collaborators reached out to Natarajan, who is well-known for her work on black holes and unseen cosmic mass. “This is a case where you could actually have a black hole forming before the stars. And that I found really exciting,” says Natarajan. The success of the model hinges on the subtle interplay between unseen matter and radiation during the cosmic dawn.
The idea that black holes existed before stars ignited alters the sequence of the cosmic timeline. If these massive objects were produced first, they could have served as gravitational anchors for early galaxies. Their immense gravity would have attracted surrounding gas, accelerating star formation and creating the densely packed, luminous galactic cores that JWST observes.
John Regan at Maynooth University in Ireland, who was not involved in the paper, praised the approach for its restraint. “What’s nice about the model is that it invokes less speculative physics than traditional primordial black hole physics,” says Regan. “Having said that, what we need ultimately will be concrete observations. We’ll need to see some ultra-early-Universe signatures of black holes, be that from gravitational waves or from some future CMB observations, to see if black holes truly existed at the very earliest times.”
What Happens Next
Qin and his team are already preparing for those necessary observations. Their immediate next step is to simulate this new formation process computationally. By running these simulations, they hope to determine what spectrum of light should be emitted from the accretion disk surrounding a not-quite-primordial black hole. They can then directly compare these specific spectral predictions to the little red dots data currently gathered by JWST. If the emission signatures match the simulations, the theory will gain substantial support.
Beyond JWST, the researchers are looking forward to future satellite missions, such as the proposed Primordial Inflation Explorer (PIXIE). If launched, the PIXIE satellite should be able to measure the CMB spectrum precisely enough to find physical evidence for their dark matter-driven black hole formation proposal. Astronomers are also monitoring gravitational wave signals, which could reveal the echoes of these ancient black holes colliding in the early universe. Combining theoretical models, JWST optical data, and future CMB spectral readings could finally confirm the true origins of these ancient black holes. The research is detailed in the journal Physical Review Letters.
— Priya Nair, science desk, AXO News