为什么准周期爆发只在低质量星系中被发现？
Why are Quasiperiodic Eruptions only Found in Low-Mass Galaxies?
AI总结：
本文利用QPE宿主黑洞质量普遍低于10^6 M⊙的观测事实约束恒星轨道，推断其必须高度偏心，并支持白矮星近 misses 重复吸积模型。
摘要：
我考察了当前产生准周期爆发（QPEs）的星系核样本。如果这种准周期性源于一颗恒星围绕中心黑洞的轨道运动，那么相关黑洞质量缺乏 ≳10^6 M⊙ 的情况，就对模型构成了严格约束。它不利于那些假设宽轨道和小偏心率的模型，因为近心点以内有充足空间，可允许 QPE 系统中存在比当前观测到的质量显著更大的黑洞。相反，如果假设绕行恒星近距离经过黑洞，那么同样缺乏大质量黑洞这一事实强烈表明，恒星轨道必须具有显著偏心率，即 1−e ≲ 几×10^-2。这支持一种潮汐瓦解“险些相遇”图景：QPEs 来自一颗绕行恒星（实际为白矮星）因引力辐射损失轨道角动量而产生的重复吸积，尽管在推导偏心率约束时并未假设这一点。鉴于当前较小观测样本所带来的严格约束，尝试在更大质量星系中寻找 QPE 系统显然非常重要。
英文摘要：
I consider the current sample of galaxy nuclei producing quasiperiodic eruptions (QPEs). If the quasiperiod results from the orbital motion of a star around the central black hole, the dearth of associated black hole masses $\gtrsim 10^6\msun$ places tight constraints on models. It disfavours those assuming wide orbits and small eccentricities, because there is ample volume within pericentre to allow significantly more massive holes in QPE systems than are currently observed. If instead the orbiting star is assumed to pass close to the black hole, the same lack of large black hole masses strongly suggests that the stellar orbits must be significantly eccentric, with $1 - e \lesssim {\rm few}\times 10^{-2}$. This favours a tidal disruption near-miss picture where QPEs result from repeated accretion from an orbiting star (in practice a white dwarf) losing orbital angular momentum to gravitational radiation, even though this is not assumed in deriving the eccentricity constraint. Given the tight constraints resulting from the current small observed sample, attempts to find QPE systems in more massive galaxies are clearly important.
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