Circumbinary accretion occurs throughout the universe, from the formation of stars and planets to the aftermath of major galactic mergers. We present an extensive investigation of circumbinary accretion disks, studying circular binaries with mass ratios (q ≡ M ₂/M ₁) from 0.01 to 1 and at each mass ratio probing the effects of disk thickness and viscosity. We study disks with aspect ratios H/r ∈ {0.1, 0.05, 0.03} and vary both the magnitude and spatial dependence of viscosity. Although thin accretion disks have previously been found to promote rapid inspirals of equal-mass binaries, we find that gravitational torques become weaker at lower mass ratios and most binaries with 0.01 ≤ q ≤ 0.04 outspiral, which may delay the coalescence of black hole binaries formed from minor mergers and cause high-mass exoplanets to migrate outward. However, in a number of cases, the disks accreting onto binaries with mass ratios ∼0.07 fail to develop eccentric modes, leading to extremely rapid inspirals. Variability in black hole accretion correlates with disk eccentricity, and we observe variability above the ∼10% level even for mass ratios of 0.01. We demonstrate that the spatial dependence of the viscosity (e.g., α vs. constant ν) significantly affects the degree of preferential accretion onto the secondary, resolving discrepancies between previous studies. Colder circumbinary disks remain eccentric even at q ∼ 0.01 and sustain deep, asymmetric cavities.

中文翻译：

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吸积双星的演化：从褐矮星到超大质量黑洞


从恒星和行星的形成到主要星系合并的后果，环双星吸积发生在整个宇宙中。我们对环双星吸积盘进行了广泛的研究，研究了质量比 (q == M ₂ /M ₁ ) 从 0.01 到 1 的圆形双星，并在每个质量比探测了圆盘厚度和粘度。我们研究长宽比为 H/r ε {0.1, 0.05, 0.03} 的圆盘，并改变粘度的大小和空间依赖性。尽管之前已经发现薄吸积盘可以促进等质量双星的快速吸气，但我们发现，在质量比较低且大多数双星具有0.01≤q≤0.04外旋时，引力扭矩会变弱，这可能会延迟形成的黑洞双星的合并来自小型合并并导致大质量系外行星向外迁移。然而，在许多情况下，吸积到质量比~0.07的双星上的圆盘无法发展出偏心模式，导致极快的螺旋。黑洞吸积的变异性与盘偏心率相关，即使质量比为 0.01，我们也观察到变异性高于 ∼10% 的水平。我们证明，粘度的空间依赖性（例如，α 与常数ν）显着影响二次粒子的优先吸积程度，从而解决了先前研究之间的差异。较冷的环双星盘即使在 q ∼ 0.01 时仍保持偏心，并维持深的、不对称的空腔。