When the telescope showed fewer galaxies than expected, the team's first thought was it was broken. It wasn't.
image from Gemini Imagen 4
JWST observations of quasar J0100+2802 reveal that supermassive black holes suppress star formation across intergalactic distances (~23 million light-years), not just within their host galaxies. The mechanism appears to be rapid photodissociation of molecular hydrogen (H2) by intense UV radiation, rather than the slower thermal heating model — destroying the raw material for stars before they can form. This finding, from observations at roughly 900 million years after the Big Bang, positions black holes as active architects of early cosmic structure rather than passive late arrivals.
Supermassive black holes don't just eat. They sterilize.
When Yongda Zhu and colleagues pointed the James Webb Space Telescope at quasar J0100+2802 — a black hole roughly 12 billion times the mass of the sun, blazing with 40,000 times the light of every star in the Milky Way combined — they expected to find galaxies clustered around it. That's the usual picture: matter flows inward, brightens, forms stars. Instead, they found fewer galaxies than the models predicted. Their first thought, Zhu told the University of Arizona: was the expensive telescope broken.
It wasn't. The galaxies were there — just quiet. Star formation in neighbors up to 7 comoving megaparsecs away had been suppressed. That's roughly 23 million light-years. A black hole had changed the ecosystem of an entire galactic neighborhood.
The paper, accepted for publication in The Astrophysical Journal Letters and originally posted to arXiv in August 2025, is now getting another round of attention. The science isn't new. What's worth your time is the mechanism — and what it means for how we think about the early universe.
The old model for how quasars suppress star formation leaned on thermal heating: the black hole pumps energy into surrounding gas, heating it up so it can't collapse into new stars. That works, but it takes time. Zhu's team looked at the timescale encoded in the suppression radius — about 3.1 million years of cumulative quasar activity — and found it was too short for thermal heating to be the main driver. The better fit is rapid photodissociation: the quasar's intense UV radiation tears apart molecular hydrogen (H2) directly, destroying the raw material stars are made from before it can coalesce. No H2, no stars. The gas doesn't need to be hot — it just needs to be gone.
This matters because the H2 channel implies a faster, more localized chokehold than thermal models predicted. The observations used JWST's NIRCam grism spectroscopy from the SAPPHIRES and EIGER programs to study 59 galaxies at redshifts 5.33 to 6.93 — roughly 900 million years after the Big Bang. At that epoch, the universe was still assembling its first massive structures. If supermassive black holes were already capable of switching off star formation across 7 cMpc, they were active architects of the early galactic landscape, not passive late-arrivals.
The scale is the thing worth sitting with. 7 cMpc is not a galactic scale — it's an intergalactic one. The Milky Way's retinue of satellite galaxies extends over roughly 1 Mpc. J0100+2802 was running a suppression field three times that radius. That's not a predator taking down nearby prey. That's a regime changer.
What triggered the quasar's radiative episode is an open question. The transverse suppression radius constrains its duration, not its origin. And whether this feedback mechanism operates the same way in the local universe — where we can actually run controlled comparisons — remains a matter of active modeling. The paper makes the case for H2 photodissociation as the dominant channel at these redshifts and luminosities. Lower-luminosity active galactic nuclei in the nearby universe may work differently.
But the picture that emerges from J0100+2802 is that supermassive black holes are not a local phenomenon. They set conditions for entire galactic clusters. When they turn on, they don't just consume — they rearrange the physics of everything around them. And at least once, about 900 million years after everything began, that rearrangement silenced an entire neighborhood of stellar nurseries.
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Research completed — 0 sources registered. JWST (via SAPPHIRES and EIGER programs) found quasar radiation suppresses star formation in neighboring galaxies out to ~7 comoving Mpc. Yongda Zhu et
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Headline selected: Black Holes Don't Just Eat — They Sterilize Star Formation
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