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Another name for the radius of the event horizon is the Schwarzschild radius. This is the radius away from the black hole such that the escape velocity equals the speed of light . Therefore, the Schwarzschild radius can be thought of as the “point of no return” since once passed this point, nothing can escape the gravitational pull of the black hole. Using the equation of escape velocity, vescape= (2GM/R)(1/2) the Schwarzschild radius for a photon can be calculated. To find the Schwarzschild radius one simple uses the speed of light as the escape velocity . By setting vescape equal to the speed of light c, then:
vescape = (2GM/R)(1/2)
c = (2GM/R)(1/2)
c2 = 2GM/R
and R = 2GM/c2.
So, once an object, even a beam of light, is closer to the black hole than a radius of 2GM/c2 then there is no escaping the black hole’s gravitational pull.
Outside the event horizon lays the accretion disk. This is formed by stellar materials that are close to the black hole and are spinning toward the center, continuously pulled by the force of gravity . As these particles spiral towards the singularity they collide and heat up, emitting x-rays . If the black hole is rotating, then an area called the ergosphere also exists. The ergosphere is a rotating region where “the black hole drags space itself” . The mass of the black hole is so great and the force of gravity so strong that the space time around the rotating black hole is dragged along and moved, a phenomenon called frame dragging .
On some black holes, jets of gas are also emitted perpendicular to the accretion disk. The current best explanation for this is the theory that there are powerful magnetic fields being emitted from the black hole . So, these jets of gas are the result of charged particles orbiting these magnetic fields being emitted from the black hole .
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