MG13 - Talk detail

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We study the tidal disruption of binaries by a massive point mass (e.g. the black hole at the Galactic centre), and we discuss how the ejection and capture preference between unequal-mass binary members depends on which orbit they approach the massive object. We show that the restricted three-body approximation provides a simple and clear description of the dynamics. The orbit of a binary with mass m around a massive object M should be almost parabolic with an eccentricity |1-e| < (m/M)^ << 1 for a member to be captured, while the other is ejected. Indeed, the energy change of the members obtained for a parabolic orbit can be used to describe non-parabolic cases. In principle, for any hyperbolic (elliptic) orbit, the heavier member has more chance to be ejected (captured), because it carries a larger fraction of the orbital energy. However, if the orbital energy is close to zero, the difference between the two members becomes small, and there is practically no ejection and capture preference. The preference becomes significant when the orbital energy is comparable to the typical energy change at the encounter. We discuss its implications to irregular satellites around giant planets, especially Triton - Neptune's largest moon. We also predict the velocity distribution of hypervelocity stars from the Galactic centre. The presentation is based on Kobayashi et al. 2012 ApJ 748, 105 and Rossi et al. 2012 in preparation.

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