A star can be tidally disrupted around a massive black hole. It has been known that the debris forms a precessing stream, which may collide with itself. The stream collision is a key process determining the subsequent evolution of the stellar debris: if the orbital energy is efficiently dissipated, the debris will eventually form a circular disk (or torus). In this paper, we have numerically studied such stream collision resulting from the encounter between a 106 Mo black hole and a 1 Mo normal star with a pericenter radius of 100 Ro. A simple treatment for radiative cooling has been adopted for both optically thick and thin regions. We have found that approximately 10 to 15% of the initial kinetic energy of the streams is converted into thermal energy during the collision. The spread in angular momentum of the incoming stream is increased by a factor of 2 to 3, and such increase, together with the decrease in kinetic energy, significantly helps the circularization process. Initial luminosity burst due to the collision may reach as high as 1041 erg sec-1 in 104 sec, after which the luminosity increases again (but slowly this time) to a steady value of a few 1040 erg sec-1 in a few times of 105 sec. The radiation from the system is expected to be close to Planckian with effective temperature of ~ 105 K.
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