Investigating effects of dark matter on photon orbits and black hole shadows

Understand

We consider Kerr black holes (BHs) surrounded by perfect dark fluid matter (PFDM), with an additional parameter ($k$) because of PFDM, apart from mass ($M$) and rotation parameter ($a$) -- the rotating PFDM BHs.

• We analyze the photon orbits around PFDM BHs and naked singularities (NSs) and emphasise the effect of PFDM on photon \emph{boomerangs}.
• Interestingly, the azimuthal oscillations first increase and then decrease for retrograde orbits, whereas they first decrease and then increase for prograde orbits, with increasing $k$.
• Unlike in the Kerr NSs, photon \emph{boomerangs} can form around rotating PFDM NSs.