In contrast to the Schwarzschild black hole, the horizon of the Kerr-Newman black hole is not spherical.
It is a generalization of the Kerr black hole which has Q=0. The Kerr-Newman black hole has three parameters, namely, M, interpreted as the mass of the black hole (as seen by an observer at infinity), charge Q, and J, interpreted as its angular momentum (it is axisymmetric). The Kerr-Newman black hole is spinning (hence it is not static) but it always spins in the same way, and is, therefore, stationary. Note that stationary and static are different concepts. The Kerr-Newman black hole is the most general type of stationary asymptotically flat black hole. The photon sphere (also known as last photon orbit) is a region of space where gravity forces photons to travel in orbits ( source). The figure on the right shows an accretion disk which is formed by diffuse material that orbits massive central bodies. More specifically, if the area of the event horizon is given by A, the black hole entropy isįigure 6: A Schwarzschild black hole. Now, one can show (to be discussed later) that a black hole that obeys “a version” of the first law of thermodynamics possesses an entropy that is proportional to the area of the event horizon. Therefore, it makes sense to suppose that the entropy of the black hole is a monotonic increasing function of the area of the event horizon. This reminds us of the behavior of the ordinary thermodynamic entropy of closed systems. According to the area theorem, the area of the event horizon of a black hole cannot decrease. It is reasonable to suppose that the entropy of a black hole should depend only on one or more of the three observable quantities, M, Q and J. After the collapse, the first hole has no magnetic field, the second hole is not a square and the third hole does not have a mountain on its surfaces ( source). Figure 4: All three different shaped “stars” collapse without preserving its properties.
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