From NewScientist (7 August 2021):
Supermassive black holes have such an intense gravitational pull that they bend light right around them, allowing us to see an “echo” of the side that would otherwise be hidden from view. We have now seen echoes of X-ray bursts from behind a black hole, confirming a prediction of general relativity.
How?
Dan Wilkins at Stanford University in California and his colleagues used the NuSTAR and XMM-Newton X-ray telescopes to observe these flashes of radiation coming from the supermassive black hole in a galaxy called I Zwicky 1. They saw that a flare of X-rays was sometimes followed by a second, slightly dimmer flash as the radiation bounced off the accretion disc in a sort of echo.
Presumably, the accretion ring, at any given point, is only a few light-seconds away from the black hole.
I really like the visual I’m imagining.
