In the crucible of extreme gravity just outside a black hole’s event horizon, spacetime warps so steeply that photons become trapped on a “cosmic racetrack” at the photon sphere—located at 1.5 Schwarzschild radii—where they can circle the hole one or more times before either escaping into the universe or vanishing past the horizon. This looping arises directly from Einstein’s field equations: light follows geodesics in curved spacetime, and in this regime those paths close on themselves, producing the dramatic rings and lensing effects captured by the Event Horizon Telescope. It’s a testament to gravity’s uncompromising control—no sugar-coating—where light itself is corralled into orbit by the black hole’s unrelenting pull.
It's wrong to confuse geodesics in spacetime with trajectories in space and the event horizon of a black hole spacetime-which is a light-like surface, which means that it doesn't represent a place one can go to-with the surface of the star that has undergone gravitational collapse and is a place one could imagine going to.
So light ``looping around a black hole" means nothing more or less than electromagnetic waves propagating around an object in space. Nothing particularly strange.
How they do so is now a standard exercise in any physics curriculum.
Incidentally, the expression ``extreme gravity", as it pertains to black holes, is misleading. There's nothing particularly extreme about it. The event horizon of a black hole spacetime simply separates the observers of that spacetime into two classes: Those that have a finite lifetime-and will encounter the singularity of the spacetime in finite proper time, which is, however, so short that they won't actually notice anything, since they'll be dead long before; and those that don't have the singularity in their future and whose lifetime isn't, therefore, affected by its presence.
Now it is possible to deduce both mass and size of an object by scattering electromagnetic waves off it; and, therefore, to deduce whether it has suffered gravitational collapse, or not. That's the interest of the pictures obtained by the Event Horizon Telescope.
Stam Nicolis : " the expression ``extreme gravity", as it pertains to black holes, is misleading. There's nothing particularly extreme about it. "
I think the convention in black hole papers seems to be to treat the word "extreme" as meaning "being far beyond the norm of our everyday experience", which is the way that the word tends to be used in common language. Some might see that as technically wrong, but it's commonplace for people to talk about (e.g.) "extreme temperatures", without their meaning absolute zero Kelvin, or infinity Kelvin!
When technical writers want to refer to something that is literally "the extreme", as in "the ultimate", they tend to deliberately use the word "extremal", instead.
In the context of our common local experiences, IMO I think it's fair to refer to the gravity of a black hole in the region r=2M to r=3M to be rather extreme! :)
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