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We study the time evolution of the Misner-Sharp mass and the apparent horizon for gravitational collapse of a massless scalar field in AdS5 space-time for both cases of narrow and broad waves by numerically solving the Einstein's equations coupled to a massless scalar field. It turns out that the Misner-Sharp mass is everywhere constant except for a rapid change across a thin shell, being characterized by stationary point of the density profile. By studying the evolution of the apparent horizon, signaling the formation of a black hole, at different times we see how asymptotically an event horizon forms. The dependence of the thermalization time on the radius of the initial black hole event horizon is also studied.
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