Can we see light from behind a black hole? In 2021, researchers reported X-ray echoes whose timing and energies matched light reflected from the far side of an accretion disk and bent around the black hole toward us.
The light travelled through the strongly curved space outside the event horizon. It did not pass through the black hole’s interior and emerge on the other side.
How the researchers described the surprising view
Dan Wilkins explained the result in the statement quoted by the 2021 article:
“Any light that goes into that black hole doesn't come out, so we shouldn't be able to see anything that's behind the black hole. The reason we can see that is because that black hole is warping space, bending light and twisting magnetic fields around itself.”
Roger Blandford put the measurement in a longer research history:
“Fifty years ago, when astrophysicists starting speculating about how the magnetic field might behave close to a black hole, they had no idea that one day we might have the techniques to observe this directly and see Einstein's general theory of relativity in action.”
Read “behind” in these comments as the far side of the material outside the event horizon. The light’s bent path is what makes that region observable; nothing in the result lets light escape from inside the black hole. The earlier story also looked ahead to improved X-ray instruments. (Update, October 2026: ESA’s planned Athena X-ray observatory, with its Wide Field Imager camera, was rescoped in 2023 as NewAthena; its formal adoption by ESA’s Science Programme Committee is expected in 2027, with launch planned for the second half of the 2030s (Wikipedia, Advanced Telescope for High Energy Astrophysics).) Those ambitions belong to future observations, while the 2021 claim rests on the XMM-Newton and NuSTAR measurements described here.
What the telescopes detected
The observations targeted the active galaxy I Zwicky 1, also written I Zw 1. Using data from XMM-Newton and NuSTAR, researchers studied bright X-ray flares associated with the environment around its central supermassive black hole.
After the main flares, they identified fainter, delayed flashes with characteristic energy shifts. The paper, published in Nature in July 2021, interpreted these as reflected photons from different parts of the disk, including its far side.
Strong gravity bent and magnified the light along paths that allowed it to reach the observer. The result was evidence for a specific prediction of general relativity in an extreme environment.
Three parts of the scene
It helps to separate the structures involved. NASA’s anatomy guide describes them:
- The event horizon is the boundary beyond which light cannot escape to a distant observer.
- The accretion disk is hot material orbiting outside that boundary as it moves toward the black hole.
- The corona is an energetic region associated with the inner disk that produces high-energy X-rays.
The observed echoes involved radiation illuminating and reflecting from material outside the horizon. Keeping those locations separate resolves the apparent contradiction in the headline.
Why call the signals echoes?
In everyday life, an echo reaches you after sound takes a longer route, often reflecting from a wall. Here, the researchers were measuring light, with reflection from the disk and the effects of strong gravity shaping its path.
The timing matters because direct and reflected light need not arrive together. The energies of the returning X-rays also contain information about their origin and the conditions along their journey.
This is not a human ear listening to a black hole. “Echo” is a useful description of a delayed response measured with X-ray telescopes.
What made these flashes interesting?
Stanford’s account of the discovery describes how Dan Wilkins noticed the smaller, later flashes while investigating the flares. Their pattern matched predictions he had been developing for reflected light near black holes.
The result depended on comparing observations with a physical model. The claim was not that a conventional photograph suddenly revealed a hidden backside, but that the measured signals had the expected properties of light following those strongly bent paths.
How gravity makes a far side visible
In general relativity, light follows paths through curved spacetime. Near a black hole, that curvature can redirect light dramatically. A part of the disk behind the black hole can therefore contribute light to an observer’s view without any ray crossing the event horizon from inside to outside.
A related effect appears on a much larger scale in gravitationally lensed images around foreground galaxies. The objects and observations differ, but both involve gravity changing the routes by which light reaches us.
The EHT image of M87’s shadow offers another comparison: a resolved radio image of a different black hole, rather than the X-ray timing measurement discussed here.
What makes the echoes remarkable is the route they reveal. Faint changes in the arrival time and energy of light let astronomers investigate a region they cannot visit—and test how gravity behaves just outside a black hole.
More images
Original feature credits and references: statement release · Wide Field Imager · Futurism.
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