For half a century, Stephen Hawking’s most famous idea came with an awkward gap in the middle. Black holes, he argued in 1974, are not perfectly black at all: they should glow faintly at the edge, slowly bleeding energy until, over unfathomable spans of time, they evaporate entirely. The prediction became one of the load-bearing walls of modern physics. What nobody could explain was the plumbing — exactly how the energy leaks out of the hole and into the radiation.
A team working with a black hole made not of collapsed matter but of light now says it has watched that leak happen, and measured it. And the answer, they report, is stranger for being so simple.
The group, led by Lorenzo Procopio at Paderborn University in Germany, describes the result in the journal Nature, with a preprint posted to arXiv on 1 July 2026. Working in a fibre-optical stand-in for a black hole’s event horizon, the physicists captured what theorists call the “backreaction” of Hawking radiation — the recoil the escaping glow exerts on the field that feeds it. That recoil is the missing piece. Radiation carries away energy; backreaction is the accounting entry on the other side of the ledger, the reason the black hole shrinks. It had never been pinned down in a lab analogue before.
Here is the part that made the researchers reach for the word “maybe.” The standard assumption, both for optical analogues and for gravity itself, was that Hawking radiation emerges through a tangled, cascading chain of interactions. Procopio’s team found something more direct. “Hawking radiation is the result of a direct process, if the interaction between the radiation and the equivalent of the gravitational field is biquadratic,” they write. Then they let themselves speculate outward: “Maybe astrophysical black holes radiate by a process as simple and direct as ours. The resulting backreaction would describe in microscopic detail how black holes evaporate.”
Why build a black hole out of light
The obvious objection writes itself — this is not a real black hole, and no one is claiming otherwise. It is an analogue, a system engineered to obey the same underlying mathematics as an event horizon so that physicists can poke at behaviour they can never reach in the sky. The trick dates back years and has been built from flowing water, ultracold atoms and, as here, pulses of laser light racing through optical fibre. Inside the fibre, a light pulse creates a moving boundary that traps other light much as gravity traps it at a horizon, and quantum jitter at that boundary produces the analogue of Hawking’s glow.
That is not a small caveat, and it cuts both ways. Real Hawking radiation from a stellar black hole is so feeble it is drowned a trillion times over by the ambient warmth of the universe; the team’s own paper notes the emission “has never been observed in astronomy, only in laboratory analogues,” and that the odds of ever catching it in space are, in their phrasing, astronomically small. If you cannot observe the thing, a table-top system that shares its equations is the next best courtroom. The question is always how much the analogue is really telling you about gravity, and how much is an artefact of the wire.
What lends this result weight is the company on the author list. Alongside Procopio and collaborators Raul Aguero-Santacruz and David Bermudez sits Ulf Leonhardt, who has spent much of his career arguing that analogue systems can be trusted to say something real about horizons. Getting a measured backreaction — not just the glow, but the reaction the glow has on its source — is the kind of milestone that camp has been chasing for years.
Hawking predicted black-hole radiation in 1974. It has never been detected from a real black hole — only in laboratory analogues. The new work is the first to measure the backreaction, the energy the radiation draws back out of the system, in an optical analogue, and it points to a single direct process rather than the long-assumed cascade.
What it does and doesn’t settle
It would be a mistake to read this as evidence that a black hole in space has now been caught evaporating. It hasn’t. What the experiment offers is a mechanism — a candidate answer to a question that has sat unresolved inside an otherwise celebrated theory, tested in a system where the numbers can actually be read off an instrument. Whether nature runs the same simple, direct process out where gravity is genuinely warping spacetime is a claim the paper floats rather than proves.
Still, the direction of travel matters. Analogue gravity has spent two decades reproducing the glow of Hawking radiation; measuring how that glow bites back closes a loop that Hawking himself left open. It also feeds the same fascination driving observational work on the real objects, from the sudden reawakening of dormant supermassive black holes to the record-breaking mergers that keep bending the theory. For a phenomenon no telescope may ever see, a black hole built from light has become a surprisingly good place to watch it come undone. A fuller account of the experiment is laid out by ScienceAlert.
