July 28, 2021

I Zwicky 1

X-ray echoes from behind a supermassive black hole are reported

The photons did not escape from inside the black hole. They reflected from superheated gas on the far side of its external accretion disk and curved around the black hole through warped spacetime.

28 July 2021: echoes after the flares

A team led by Dan Wilkins published observations on 28 July 2021 of X-ray flares around the supermassive black hole in the galaxy I Zwicky 1, roughly 800 million light-years away.

After the bright flares, the researchers detected smaller, delayed flashes whose energies were shifted in a way consistent with the original radiation reflecting off the far side of the accretion disk and bending around the black hole.

Inferred from timing, not photographed

The data came from ESA's XMM-Newton and NASA's NuSTAR. Neither resolved a picture of the black hole's far side; the team placed the echoes' origin using their delays and wavelength shifts.

"Direct observation" is journalistic shorthand, and the paper's own wording is careful: the flashes were consistent with emission re-emerging from behind the black hole. The general-relativistic reading is model-based, though strongly supported.

What the X-rays were, and were not

The radiation did not come from inside the event horizon, and it was not visible light. X-rays produced near the black hole reflected from the far side of the external accretion disk and were bent into Earth's line of sight.

Nor was this a first confirmation of general relativity, which had already passed many tests; it probed one particular strong-gravity prediction. The work had begun as a study of the black hole's corona, and the smaller echoes trailing the main flares were the unexpected find.

Sources

Researched 23 Aug 2026 4 sources 2 audit passes

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What the sources leave uncertain

“Direct observation” is journalistic shorthand. The telescopes did not resolve a photograph of the black hole's rear side; researchers inferred the photons' paths from their delays and energy shifts.
The paper's cautious wording says the flashes were “consistent with” emission re-emerging from behind the black hole. The general-relativistic interpretation is model-based, though strongly supported.
The radiation did not emerge from inside the event horizon. It originated near the black hole, reflected from the far side of the external accretion disk and was bent into our line of sight.