Fabiano Feleppa

The Event Horizon Telescope looks at M87* and sees more than just a ring of light around a dark void. That light is twisted, like a corkscrew. The wavefront carries a helical structure that physicists call orbital angular momentum.

A cosmic ray approaches a black hole almost tangentially. Instead of falling straight in, it lingers on an unstable orbit, like an acrobat balancing on a tightrope over an abyss. After a few loops, the light finally escapes toward a distant observer. Such rays produce multiple images of the same source, known as higher-order images.