Superradiant evolution of the shadow and photon ring of Sgr A$^\star$

Understand

Ultralight bosons can affect the dynamics of spinning black holes (BHs) via superradiant instability, which can lead to a time evolution of the supermassive BH shadow.

• We study prospects for witnessing the superradiance-induced BH shadow evolution, considering ultralight vector and tensor fields.
• We introduce two observables sensitive to the shadow time-evolution: the shadow drift, and the variation in the azimuthal angle lapse associated to the photon ring autocorrelation.
• The two observables are shown to be highly complementary, depending on the observer's inclination angle.