近地平线潮汐瓦解事件
Near-Horizon Tidal Disruption Events
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中文总结 AI 辅助
本研究识别出一类发生在快速自转大质量黑洞附近、潮汐瓦解半径接近引力半径的“近地平线TDEs”，通过克尔测地线计算发现束缚轨道产生更高回落率，可解释超亮事件ASASSN-15lh，为强场引力提供新探针。
中文摘要 AI 辅助
潮汐瓦解事件（TDEs）为探测超大质量黑洞（SMBHs）周围的时空几何提供了独特的动力学探针。虽然传统的TDEs发生在质量约为 $M_\bullet \sim 10^6 - 10^7 M_\odot$ 的超大质量黑洞周围，此时恒星在事件视界远处被瓦解，但我们在此识别出一类特殊的TDEs，它们发生在质量 $M_\bullet \gtrsim 10^8 M_\odot$ 的快速自转超大质量黑洞周围，其潮汐瓦解半径接近引力半径。我们将这些事件称为“近地平线TDEs”，并通过计算克尔时空中的测地线，研究地平线的邻近性如何改变碎片演化及随后的回落过程。我们发现，对于以抛物线轨道遭遇超大质量黑洞的恒星，高达约 $(90\\%-95\\%)$ 的恒星碎片要么直接坠入超大质量黑洞，要么逃逸出系统。相比之下，束缚轨道保留了显著更大比例的碎片。利用由此得到的碎片分布，我们计算了回落率，发现束缚轨道产生的峰值回落率本质上更高，且衰减时标更短，相对于抛物线轨道约为 $\sim 10^3$ 倍。然而，当恒星轨道角动量特别低时，峰值回落率可能因碎片损失到坠入轨道而大幅降低。这种快速回落与质量亏损的结合自然地解释了诸如ASASSN-15lh等超亮TDEs，而标准TDE模型一直难以重现这些事件。我们的工作确立了近地平线TDEs作为强场引力的新探针，以及识别大质量、快速自转超大质量黑洞的有力工具。
英文摘要
Tidal disruption events (TDEs) offer a unique dynamical probe of the spacetime geometry around supermassive black holes (SMBHs). While conventional TDEs occur around SMBHs of $M_\bullet \sim 10^6 - 10^7 M_\odot$, where stars are disrupted far from the event horizon, here we identify a special class of TDEs around rapidly spinning SMBHs with masses $M_\bullet \gtrsim 10^8 M_\odot$, where the tidal-disruption radius approaches the gravitational radius. We term these events "near-horizon TDEs" and, by calculating geodesics in Kerr spacetime, investigate how the proximity of the horizon modifies the debris evolution and subsequent fallback. We find that for stars encountering the SMBH on parabolic orbits, up to $\sim (90 \%-95 \%)$ of the stellar debris either plunges directly into the SMBH or escapes the system. Bound orbits, by contrast, retain a substantially larger fraction of the debris. Using the resulting debris distribution, we calculate the fallback rates and find that bound orbits produce intrinsically higher peak fallback rates and shorter decay timescales, by factors of $\sim 10^3$ relative to parabolic orbits. However, when the stellar orbital angular momentum is particularly low, the peak fallback rate can be substantially suppressed by debris lost to plunge orbits. This combination of rapid fallback and a mass deficit naturally explains overluminous TDEs such as ASASSN-15lh, which standard TDE models have struggled to reproduce. Our work establishes near-horizon TDEs as a new probe of strong-field gravity and a promising tool for identifying massive, rapidly spinning SMBHs.
发表机构
- Peking University（北京大学）
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