Conic Section on the Sky: Shadows of Linearly Superrotated Black Holes

Soft hairs are intrinsically infrared features of a black hole, which may also affect near-horizon physics. In this work, we study one of the primary observables through which we can study the effects of a particular type of soft hair in Einstein's gravity: the shadow of a non-rotating black hole implanted with linear { regular} superrotational hair. We show that such soft hairs deform the shadow from the characteristic circular shape of bald Schwarzschild black holes into ellipses. Such a unique effect can be observed in future black hole imaging projects. This starkly contrasts with the supertranslated counterpart, for which the only changes are the static shift of the circular shadow's position and thus cannot be detectable. Our results demonstrate the richness of observable effects due to the infrared structures of Einstein's gravity.