Sungsoo S. Kim(1,4), Myeong-Gu Park(2), Hyung Mok Lee(3,5)

(1) Department of Physics, Korea Advanced Institute of Science & Technology, Daejon 305-701, Korea
(2) Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Taegu 702-701, Korea
(3) Department of Earth Sciences, Pusan National University, Pusan 609-7= 35, Korea
(4) This work has been initiated when he was at Institute for Basic Sciences, Pusan National University, Korea
(5) Current address: Department of Astronomy, Seoul National University, Seoul 151-742, Korea;

Paper: Accepted for publication in ApJ

EPrint Server: astro-ph/990213201


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.

Preprints available from the authors at , or the raw TeX (no figures) if you click here.

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