When the universe was barely 750 million years old, a supermassive black hole launched a jet of material almost directly at Earth.

Researchers have discovered VLASS J041009.05−013919.88, a blazar residing in the epoch of reionization. This marks the most distant blazar ever confirmed. The object harbors a black hole weighing approximately 700 million times the mass of our sun, all wrapped in a cosmic engine that defies expectations about how quickly such monsters could grow.

Blazars are rare. They're quasars whose relativistic jets happen to point toward us, amplifying their brightness through a trick of physics. Finding one this far back in time raises immediate questions about what else might be lurking in the early universe.

Radio Whispers Across Cosmic Time

The discovery began with a systematic search. Scientists cross-matched optical surveys with radio observations, hunting for objects invisible in visible light but screaming in radio wavelengths. J0410−0139 fit the profile perfectly: undetected in optical bands, yet producing strong radio emission at 1.4 and 3 gigahertz.

The clincher came from observing the radio flux increase by 35 percent between two observation epochs separated by less than three years in the observer's frame. Variability at this level suggested something extraordinary.

Spectroscopic confirmation arrived on November 7, 2020. A 30-minute exposure revealed a prominent Lyman-alpha emission line placing the quasar at redshift 7.0. Follow-up observations with near-infrared spectrographs detected characteristic broad emission lines including carbon IV and magnesium II, standard signatures of actively accreting supermassive black holes. The spectral slopes and emission line profiles remained consistent across multiple observations spanning a year, indicating stability in the accretion disk and broad line region.

Five Signatures of Extreme Physics

Blazars announce themselves through distinctive observational fingerprints. J0410−0139 satisfies all five criteria used to identify these objects.

First: strong variable radio emission. The source exhibited flux density changes by a factor of three over just 14 days in the quasar's rest frame. Radio observations spanning from 1 to 12 gigahertz revealed dramatic spectral evolution. In 2021, the spectrum showed a turnover around rest-frame 40 gigahertz, characteristic of gigahertz-peaked radio sources. By 2022, the spectrum had flattened considerably.

Second: flat or peaked radio spectrum. The observed spectral behavior resembles blazars at lower redshifts and suggests either a young jet or a flaring event.

Third: compact radio morphology. Very Long Baseline Array observations at 1.5 gigahertz achieved a resolution of 75 by 37 parsecs, resolving a dominant marginally-resolved source with a flux density of 4.46 milliJansky. The derived brightness temperature exceeds two billion Kelvin, demanding relativistic motion.

Fourth: hard X-ray emission. Combined observations from XMM-Newton and Chandra yielded an X-ray photon index of 1.47, significantly harder than the average value of 2.4 found in other redshift-greater-than-six quasars. The X-ray luminosity in the 2 to 10 kiloelectronvolt band reaches 3.2 times 10 to the 45th ergs per second.

Fifth: favorable X-ray to ultraviolet flux ratio. The rest-frame 10 kiloelectronvolt to 2,500 angstrom flux ratio measured at negative 1.25 exceeds the threshold of negative 1.36 used to classify blazars, confirming jet-dominated emission.

The Population Hiding in Plain Sight

The existence of one blazar at this epoch implies a much larger population of similar objects whose jets don't point toward us. Basic geometry provides the constraint. If the bulk Lorentz factor of the jet's emitting plasma falls between 4 and 15—typical values for blazars—then somewhere between 30 and 450 similar jetted sources should exist at comparable redshifts.

Only two other spectroscopically confirmed jetted quasars are known at similar distances, around redshift 6.8. Many more await discovery.

But here's where things get interesting. The radio loudness parameter for J0410−0139 ranges from 74 to 331 depending on observation epoch and measurement method. This firmly places it in the radio-loud category by conventional definitions. However, relativistic Doppler boosting could enhance the observed flux by factors of 7 to 15, potentially making an intrinsically weak jet appear radio-loud.

Two scenarios emerge, each with profound implications.

Scenario One: Universal Jets

If J0410−0139 hosts an intrinsically weak jet that appears bright only due to beaming, then the argument for 2Γ² similar sources still holds. The expected number approaches the total number of ultraviolet-bright quasars predicted by the redshift-seven quasar luminosity function. The implication: a large fraction—perhaps most—ultraviolet-bright quasars must harbor relativistic radio jets, even those classified as radio-quiet.

This aligns with recent findings. Some of the most massive known high-redshift quasars show evidence of relativistic jets despite radio-quiet classifications. At low redshift, the origin of radio emission in radio-quiet quasars remains debated, but examples exist of active galactic nucleus-powered relativistic jets that don't meet observational thresholds for radio-loud classification.

Star formation contributes negligibly to J0410−0139's radio luminosity—less than four orders of magnitude of what's observed.

Confirmation that most high-redshift quasars are jetted carries profound implications. Relativistic jets can disrupt the interstellar medium of host galaxies and potentially enhance supermassive black hole growth rates.

Scenario Two: Hidden Growth

If J0410−0139 is intrinsically radio-loud, then approximately ten times more radio-quiet quasars should exist at similar redshifts. This prediction conflicts sharply with expectations from the quasar ultraviolet luminosity function.

Reconciliation requires that most black hole growth happens in an obscured phase. Theoretical models predict such obscured growth, and observational support comes from a recently discovered obscured redshift 6.8 quasar and intrinsically luminous candidate active galactic nuclei uncovered by the James Webb Space Telescope.

The black hole mass of 6.9 times 10 to the eighth solar masses and Eddington ratio of 1.22 match properties observed in other comparable-epoch quasars lacking powerful jets. Growing a black hole this massive this quickly challenges standard models.

Rethinking Black Hole Formation

The presence of J0410−0139 suggests that jet-enhanced or obscured super-Eddington accretion can play crucial roles in early supermassive black hole growth. Both scenarios ease tensions regarding how such massive black holes could form so early.

Jets might enhance accretion efficiency. Alternatively, sustained super-Eddington accretion occurring in heavily obscured environments could build supermassive black holes rapidly while remaining hidden from ultraviolet surveys.

These mechanisms don't eliminate the need for massive seeds—dense star cluster collapse or population III star remnants remain viable options—but they relax some constraints on how those seeds must grow.

Looking Forward

The radio-loud fraction of quasars remains constant at approximately 10 percent from low redshift to redshift six. If this fraction holds at redshift seven and J0410−0139 represents a typical radio-loud source, then a substantial population of radio-quiet quasars must exist nearby in cosmic time, many perhaps obscured.

The discovery demonstrates that systematic radio surveys can uncover populations missed by optical selection. As radio facilities continue surveying the sky and new instruments probe deeper into the epoch of reionization, the full census of jetted sources in the first billion years will emerge.

For now, one thing seems certain: the early universe was more active, more violent, and more complex than models predicted. Somewhere out there, hundreds of jets pierce the neutral hydrogen fog, pumping energy into gas that will eventually ignite the first galaxies. Most point away from us. We found the one that didn't.

Credit & Disclaimer: This article is a popular science summary written to make peer-reviewed research accessible to a broad audience. All scientific facts, findings, and conclusions presented here are drawn directly and accurately from the original research paper. Readers are strongly encouraged to consult the full research article for complete data, methodologies, and scientific detail. The article can be accessed through https://doi.org/10.1038/s41550-024-02431-4