Astronomers studying the earliest galaxies have found that the James Webb Space Telescope is revealing supermassive black holes buried so deeply in dust that decades of optical and X-ray surveys missed them entirely. One striking case, a galaxy called Virgil at a spectroscopic redshift of 6.6379, looks like an ordinary star-forming system in ultraviolet and optical light but harbors an actively growing black hole visible only in mid-infrared wavelengths. The discovery is part of a broader pattern: multiple JWST programs now report that the number of obscured, actively accreting black holes in the early universe far exceeds previous estimates built from X-ray data alone.
Why mid-infrared detection is rewriting the black hole census
For two decades, the standard method for counting growing supermassive black holes relied on X-ray telescopes like Chandra and XMM-Newton. X-rays can penetrate moderate amounts of gas and dust, so surveys assumed they captured most active galactic nuclei, or AGN. A 2005 study published in Nature established that dust obscures most supermassive black hole growth and that mid-infrared selection could recover type-2 quasar populations invisible to other methods. That finding raised an alarm, but the instruments available at the time could not push the search to the highest redshifts where galaxies were forming their first massive black holes.
JWST’s Mid-Infrared Instrument, known as MIRI, changed the equation. Operating at wavelengths between roughly 5 and 28 micrometers, MIRI can detect thermal emission from AGN-heated dust even when the surrounding cocoon of material is thick enough to block X-rays. The hypothesis that a simple color cut, comparing brightness in the NIRCam F444W filter against the MIRI F1500W filter, could flag these hidden objects is now being tested across multiple deep survey fields. Per an analysis of the galaxy Virgil, the source exhibits an extreme red color of F444W–F1500W equal to 2.84 plus or minus 0.04 mag, a signature consistent with hot dust heated by an obscured AGN rather than by young stars alone. Without MIRI data, Virgil registers as a standard Lyman-alpha emitter during the epoch of cosmic reionization, roughly 800 million years after the Big Bang.
This approach effectively inverts the logic of traditional AGN searches. Instead of looking for high-energy photons that escape the obscuring material, astronomers look for the reradiated glow of dust grains heated to a few hundred kelvins. The mid-infrared excess stands out when compared with the galaxy’s stellar emission in the near-infrared, allowing even compact, faint systems to be tagged as AGN candidates. Because these color selections can be applied uniformly across large imaging surveys, they provide a powerful statistical handle on how many black holes were actively growing at early times.
CEERS, MEOW, and the scale of the missing population
The Virgil case is not isolated. CEERS Key Paper VI, published in The Astrophysical Journal Letters volume 950 in June 2023, reported that MIRI observations in the Cosmic Evolution Early Release Science field identified heavily obscured AGN at redshifts above 3 that Chandra X-ray data had not flagged. According to that study, the inferred black-hole accretion density exceeded X-ray-based results by approximately 0.5 dex, a factor of roughly three. That gap is large enough to reshape models of how black holes grew alongside their host galaxies in the first few billion years of cosmic history.
A separate program called the MIRI Early Obscured AGN Wide Survey, or MEOW, extended the search across a broader redshift range from 0 to 6. Its results show AGN abundances higher than both UV-selected luminosity functions and X-ray-based estimates, according to the MEOW analysis. The consistency between CEERS and MEOW strengthens the case that mid-infrared selection is not simply finding a few unusual objects but is instead recovering a large, systematically missed population of growing black holes.
A parallel line of evidence comes from direct comparisons between JWST-selected AGN candidates and deep Chandra imaging. One study cross-matching the two datasets found that many JWST-identified AGN are either Compton-thick, meaning their surrounding gas columns are dense enough to absorb even hard X-rays, or intrinsically weak in X-rays. Either explanation means that X-ray surveys, long considered the gold standard for black hole census work, have a blind spot that grows more severe at higher redshifts where dust and gas fractions increase.
These results carry significant implications for cosmic history. If a substantial fraction of black hole growth occurred in such buried phases, then the energy output from accretion-mostly emitted in the infrared-may have played a larger role in heating and stirring the interstellar medium of young galaxies than previously thought. The revised accretion history also feeds back into models of how quickly black holes reached masses of a billion suns by redshifts of 6 and beyond, a long-standing challenge for theorists trying to explain the luminous quasars seen when the universe was less than a billion years old.
The “little red dots” puzzle and competing interpretations
Not every JWST-discovered compact red source fits neatly into the obscured AGN framework. A class of objects nicknamed “little red dots,” or LRDs, has complicated the picture. These sources often display broad hydrogen Balmer emission lines, a classic AGN signature, yet many lack detectable X-ray, radio, and mid-infrared emission, according to a Nature Astronomy report on their apparent transition into quasars. That combination is difficult to reconcile with standard AGN models, which predict that broad-line objects should produce detectable emission across multiple wavelength bands.
The tension arises because broad emission lines are usually associated with gas orbiting close to the black hole, within a few light-days to light-weeks, where velocities reach thousands of kilometers per second. In conventional unification schemes, seeing this region implies a relatively unobscured line of sight to the central engine. If that is the case, the accretion disk and its corona should emit strongly in the ultraviolet and X-ray, while surrounding dust should glow in the mid-infrared. LRDs, by contrast, seem to show the broad-line region without the expected multiwavelength signatures.
Several explanations have been proposed. One possibility is that some LRDs host black holes accreting at extreme rates relative to their mass, producing unusual spectral energy distributions that peak in the optical and near-infrared while remaining faint in X-rays. Another is that their X-ray emission is scattered or absorbed in ways not captured by simple models, perhaps due to complex, clumpy structures in the inner regions. A more radical idea is that a subset of LRDs might not be powered by conventional AGN at all but by exotic stellar processes or transient events that mimic broad-line profiles.
Virgil and similar mid-infrared-bright systems help anchor one end of this spectrum, representing heavily buried AGN where dust reprocessing dominates the observable output. LRDs, with their puzzling mix of broad lines and weak high-energy signatures, occupy the other end, challenging astronomers to refine their understanding of how black holes light up their surroundings. Together, they underscore that JWST is not just adding more examples to known categories but is exposing gaps in the taxonomy itself.
What comes next for JWST and early black holes
The emerging picture from MIRI surveys, color-selected candidates like Virgil, and enigmatic populations such as the little red dots suggests that the early universe hosted a far more diverse set of black hole growth modes than previously appreciated. To turn this qualitative realization into a quantitative census, astronomers will need larger, uniformly selected samples with spectroscopic confirmation and coordinated follow-up across the electromagnetic spectrum.
Future JWST programs aim to combine deep MIRI imaging with NIRSpec spectroscopy to measure black hole masses, accretion rates, and host galaxy properties for statistically meaningful samples at redshifts above 5. At the same time, longer Chandra exposures and upcoming X-ray missions will test whether current non-detections truly reflect intrinsic X-ray weakness or simply push against the sensitivity limits of existing data. Radio interferometers and submillimeter observatories will probe jets and cold gas reservoirs, offering complementary views of how these buried engines interact with their environments.
As these efforts unfold, Virgil’s mid-infrared glow and the curious behavior of the little red dots will serve as touchstones. They highlight both how much black hole growth has been hiding in plain sight and how incomplete our theoretical frameworks remain. JWST’s ability to see through the dust is forcing a revision of the cosmic black hole growth story-one in which obscured, unconventional, and still-mysterious phases may turn out to be the rule rather than the exception.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
