It so happens that a black hole photosphere is about 1.5 times the Schwarzschild radius of the black hole. The photosphere is a boundary such that if a beam of light or a photon were to be directed in a manner tangent to the surface of the imaginary photosphere of a black hole, the photon would in theory orbit the black hole for an eternity under the simplified model that black holes are eternal.
In reality, black holes have a finite life time due to the process of Hawking Radiation Emission. Hawking Radiation is a theoretical consequence of a process by which zero point vacuum field fluctuations or virtual particle pairs that form within a radial distance out from the event horizon of the black hole such that one of the particles falls into the black hole while the other particle such as a photon escapes to leave the vicinity of the black hole.
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