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arXiv 1002.0584astro-ph.CO
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气体驱动的大质量黑洞双星:nHz引力波背景中的特征

Gas driven massive black hole binaries: signatures in the nHz gravitational wave background

Bence Kocsis, Alberto Sesana

摘要:

脉冲星定时阵列(PTA)测量了周期在0.1-10年之间的大质量黑洞双星(MBHB)产生的nHz频率引力波(GW)。以前的研究nHz GW背景假设的inspiral是纯粹由GW驱动。然而,由气体盘产生的扭矩可以比GW发射更有效地收缩二进制,减少这些分离的二进制数。我们使用简单的磁盘模型的circumbinary气体和二进制磁盘的相互作用,通过物理上不同的磁盘区域的MBHB的轨道衰变,直到GWs接管他们的演变。我们提取MBHB宇宙合并率从千年模拟,产生Monte Carlo实现的人口的气体驱动的二进制文件,并计算相应的GW振幅最明亮的个人二进制文件和随机GW背景。对于α>0.1的稳态α盘,我们发现nHz GW背景可以被显著修改。然而,可分辨的二进制文件的数量不会因气体的存在而改变;我们预测1-10个单独可分辨的源可以在1-50 ns的定时精度下高于噪声。气体驱动的迁移主要减少了小的总质量或不等质量比的双星的数量,这导致了平均随机GW-背景的衰减,但增加了单独可分辨的双星的检测意义。结果对双星-盘相互作用模型是敏感的。对于Ivanov,Papaloizou和Polnarev(1999)的时间依赖模型,GW背景没有显著衰减。

英文摘要:

Pulsar timing arrays (PTAs) measure nHz frequency gravitational waves (GWs) generated by orbiting massive black hole binaries (MBHBs) with periods between 0.1-10 yr. Previous studies on the nHz GW background assumed that the inspiral is purely driven by GWs. However, torques generated by a gaseous disk can shrink the binary much more efficiently than GW emission, reducing the number of binaries at these separations. We use simple disk models for the circumbinary gas and for the binary-disk interaction to follow the orbital decay of MBHBs through physically distinct regions of the disk, until GWs take over their evolution. We extract MBHB cosmological merger rates from the Millennium simulation, generate Monte Carlo realizations of a population of gas driven binaries, and calculate the corresponding GW amplitudes of the most luminous individual binaries and the stochastic GW background. For steady state alpha-disks with alpha>0.1 we find that the nHz GW background can be significantly modified. The number of resolvable binaries is however not changed by the presence of gas; we predict 1-10 individually resolvable sources to stand above the noise for a 1-50 ns timing precision. Gas driven migration reduces predominantly the number of small total mass or unequal mass ratio binaries, which leads to the attenuation of the mean stochastic GW--background, but increases the detection significance of individually resolvable binaries. The results are sensitive to the model of binary--disk interaction. The GW background is not attenuated significantly for time-dependent models of Ivanov, Papaloizou, & Polnarev (1999).

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