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arXiv 2108.01140astro-ph.HE
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超大质量黑洞潮汐流循环的两种状态

Two regimes of tidal-stream circularization by supermassive black holes

Joseph Rossi, Juan Servin, Michael Kesden

摘要:

过于接近超大质量黑洞(SMBH)的恒星可能会被SMBH的潮汐引力场破坏。由此产生的碎片形成一个绕SMBH的潮汐流,由于相对论性拱点进动,它可以与自己相撞。这些自碰撞耗散能量,导致流循环。我们进行运动学模拟这些流的自碰撞,以估计作为SMBH质量$M_\bullet$和渗透因子$β$,潮汐半径的近心点距离的比率的函数,这种循环的效率。我们发现两个不同的制度,这取决于最紧密结合的碎片循环的时间$t_c$是否大于或小于质量回落率峰值的时间$t_{\rm fb}$。在慢圆化区($t_c > t_{\rm fb}$)中,在流自碰撞中耗散的能量的辐射热光变曲线在$t > t_{\rm fb}$处具有单峰,但在快圆化区($t_c < t_{\rm fb}$)中具有两个峰(一个在$t < t_{\rm fb}$处,第二个在$t_{\rm fb}$处)。对于$β\lesssim (\gtrsim) (M_\bullet/10^6M_\odot)^{-2/3}$,当拱点进动角小于(大于)0.2弧度时,潮汐流将在慢(快)区域循环。在这两个制度之间的过渡附近的测热TDE光变曲线的显著双峰的观察将有力地支持我们的模型的潮流运动学。

英文摘要:

Stars that approach a supermassive black hole (SMBH) too closely can be disrupted by the tidal gravitational field of the SMBH. The resulting debris forms a tidal stream orbiting the SMBH which can collide with itself due to relativistic apsidal precession. These self-collisions dissipate energy, causing the stream to circularize. We perform kinematic simulations of these stream self-collisions to estimate the efficiency of this circularization as a function of SMBH mass $M_\bullet$ and penetration factor $β$, the ratio of the tidal radius to the pericenter distance. We uncover two distinct regimes depending on whether the time $t_c$ at which the most tightly bound debris circularizes is greater or less than the time $t_{\rm fb}$ at which the mass fallback rate peaks. The bolometric light curve of energy dissipated in the stream self-collisions has a single peak at $t > t_{\rm fb}$ in the slow circularization regime ($t_c > t_{\rm fb}$), but two peaks (one at $t < t_{\rm fb}$ and a second at $t_{\rm fb}$) in the fast circularization regime ($t_c < t_{\rm fb}$). Tidal streams will circularize in the slow (fast) regime for apsidal precession angles less (greater) than 0.2 radians which occur for $β\lesssim (\gtrsim) (M_\bullet/10^6M_\odot)^{-2/3}$. The observation of prominent double peaks in bolometric TDE light curves near the transition between these two regimes would strongly support our model of tidal-stream kinematics.

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