A Puzzle with No Picture on the Box ✛

Original: "Towards independent event horizon imaging of the supermassive black holes in M87 and the Milky Way"
arXiv:2608.19675v1 · 2026-08-20 · CC BY 4.0 · 2 min
An algorithm assembles an image of a black hole from 'unspoiled' data fragments, without trusting telescope calibration.

A network of radio telescopes scattered across the planet catches the whisper of a distant black hole. Each antenna records a signal, but how do you combine these recordings if the clocks at the stations tick at different rates and the atmosphere distorts incoming waves? Usually, data are first 'calibrated'—adjusted to a reference, but the reference itself can be wrong. Then the image turns out like a puzzle assembled from crooked pieces.

Astronomers found a workaround: combine signals so that errors from individual stations cancel each other out. Such combinations are called closure invariants: they are independent of calibration, like checking the sum of angles in a triangle without trusting the protractor.

These 'honest' fragments are exactly what the GenDIReCT algorithm is fed. It works like an experienced restorer: first, it learns from thousands of ordinary photographs (cats, airplanes, cars) and then it takes an incomplete set of closure invariants and fills in the picture. No astrophysical templates: the model doesn't know how a black hole 'should' look, so it doesn't force the result to match expectations.

The test on real data is impressive. For the blazar 3C279, the algorithm distinguished three bright clumps, and one of them moved at an apparent speed ten times faster than light — an illusion created by a relativistic jet aimed almost directly at us. For Centaurus A, it produced two glowing edges along the jet, and their opening angle matched what the Event Horizon Telescope had previously found.

The secret is that closure invariants carry information about the source structure but are blind to systematic errors. It's like assembling a puzzle where each piece is guaranteed to be authentic, even though it's not labeled.

Previously, only the EHT collaboration produced images of event horizons, and skeptics asked: isn't the complex processing injecting what we want to see? Now there's an independent witness. It was trained on earthly pictures, yet it spotted cosmic jets, so those jets really are in the data, not in the astronomers' imagination.

The puzzle with no picture on the box is assembled. And although details are missing, the overall silhouette is unmistakable: we're looking at the vicinity of a black hole, seen without a single trusted telescope.

Closure invariants were used as early as the 1960s to discover the double structure of the radio galaxy Cygnus A without precise antenna calibration. In this work, the algorithm is trained on photographs of cats and airplanes from the CIFAR-10 dataset, yet it still recovers astrophysical jets.

In Carl Sagan's novel 'Contact', the protagonist uses interferometry to detect an extraterrestrial signal; here a similar principle is applied to imaging black holes. In the movie 'Interstellar', the image of Gargantua was created using simulations, not real observations — GenDIReCT brings us closer to obtaining such pictures from data.

Scientists
David DeutschErwin SchrödingerJohn Stewart BellLouis de BroglieLov GroverPaul Benioff
Concepts
EHT m87 event horizon apparent horizon very long baseline interferometry black hole entropy analog black hole Bekenstein-Hawking entropy vlt extreme mass ratio inspiral gravastar supernova 1987a hills mechanism hawking radiation anomalies black hole Hubble Space Telescope horizon area milky way central black hole eccentric black hole binary