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arXiv 2201.07816astro-ph.HEastro-ph.GAastro-ph.SR
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环双星吸积中圆盘厚度和粘度的调查:双星演化、变率和圆盘形态

A Survey of Disc Thickness and Viscosity in Circumbinary Accretion: Binary Evolution, Variability, and Disc Morphology

Alexander J. Dittmann, Geoffrey Ryan

摘要:

大部分的参数空间有关的天体物理学的环双星吸积盘的演变仍然没有探索。我们已经进行了一套circumbinary光盘模拟调查光盘厚度和运动粘度,使用恒定的$ν$和恒定的$α$处方。我们主要关注$0.1$和$0.033$之间的圆盘纵横比,以及$ν=0.0005$和$ν=0.008$之间的粘度(以二进制半长轴和轨道频率为单位),并专门研究圆形等质量二进制。这两个因素都强烈影响着二元半长轴的演变:在$ν=0.0005,$,吸气发生在纵横比$\lesssim0.059$,而在$ν=0.004$,吸气只发生在纵横比$\lesssim0.04$。吸气的发生主要是因为越来越强的负扭矩上的二进制流的材料落后的二进制,与可以忽略不计的贡献,从共振扭矩激发的circumbinary光盘。我们发现,减少吸积率发生时,模拟初始化太远,从最终的准稳态驱动的相互作用与二进制,而不是内在联系的光盘纵横比。我们发现,不仅腔的大小增加,粘度降低,但薄circumbinary光盘变得更加偏心。我们的研究结果表明,超大质量黑洞双星应该被驱动,比以前的估计更快,从$\sim$秒差距的距离,引力波驱动他们的inspiral,可能会减少脉冲星定时阵列可观测到的双星的数量。

英文摘要:

Much of the parameter space relevant to the evolution of astrophysical circumbinary accretion discs remains unexplored. We have carried out a suite of circumbinary disc simulations surveying both disc thickness and kinematic viscosity, using both constant-$ν$ and constant-$α$ prescriptions. We focus primarily on disc aspect ratios between $0.1$ and $0.033$, and on viscosities between $ν=0.0005$ and $ν=0.008$ (in units of binary semi-major axis and orbital frequency), and specialise to circular equal-mass binaries. Both factors strongly influence the evolution of the binary semi-major axis: at $ν=0.0005,$ inspirals occur at aspect ratios $\lesssim0.059$, while at $ν=0.004$ inspirals occur only at aspect ratios $\lesssim0.04$. Inspirals occur largely because of the increasingly strong negative torque on the binary by streams of material which lag the binary, with negligible contributions from resonant torques excited in the circumbinary disc. We find that reductions in accretion rate occur when simulations are initialised too far from the eventual quasi-steady state driven by interaction with the binary, rather than being intrinsically linked to the disc aspect ratio. We find not only that the cavity size increases as viscosity is decreased, but that thinner circumbinary discs become more eccentric. Our results suggest that supermassive black hole binaries should be driven, more rapidly than previous estimates, from $\sim$parsec separations to distances where gravitational waves drive their inspiral, potentially reducing the number of binaries observable by pulsar timing arrays.

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