Where do light rings go when a black hole is forming?

The glowing ring around a black hole image traces light orbiting in an unstable 'photon sphere' — but all previous theory assumed the black hole just sat there. This work builds a covariant framework that follows the photon sphere through genuinely time-varying spacetimes: stellar collapse, matter accretion, Hawking evaporation. The static textbook results emerge as a special case, and the dynamic behavior reveals subtleties relevant to real astrophysical events and future gravitational-wave observations.