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arXiv 2407.08705astro-ph.HE
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探测来自超大质量黑洞双星的引力波各向异性

Detecting Gravitational Wave Anisotropies from Supermassive Black Hole Binaries

Anna-Malin Lemke, Andrea Mitridate, Kyle A. Gersbach

AI总结:

本研究针对脉冲星计时阵列未探测到引力波各向异性的现状,计算现有及未来PTA的探测概率,证明未探测结果与超大质量黑洞双星起源假设不矛盾,并识别出易产生可探测各向异性的SMBHB族群,可用于表征该族群特征。

摘要:

多个脉冲星计时阵列(Pulsar Timing Array, PTA)合作项目近期已发现存在弥漫于银河系的引力波背景(gravitational wave background, GWB)的证据。该背景的起源目前仍未明确。尽管并合过程中的超大质量黑洞双星(supermassive black hole binaries, SMBHB)发出的引力波辐射是其起源的首要候选解释,但学界也提出了多种宇宙学起源的可能。由SMBHB产生的引力波背景的一个显著特征是存在GWB各向异性,这种各向异性源于局域宇宙中双星的分布情况。然而,迄今为止开展的所有各向异性搜索均未报告探测到相关信号。\n在本研究中,我们证明目前未探测到各向异性的结果,与引力波背景起源于SMBHB的假设并不矛盾。我们通过计算现有及未来PTA的各向异性探测概率得出了这一结论。研究发现,具备NANOGrav 15年数据集噪声特性的PTA,探测到SMBHB产生的各向异性的概率仅约2%-11%,具体概率取决于SMBHB族群的属性。不过我们估计,对于IPTA DR3数据集,这些探测概率将提升至约4%-28%,若仍未探测到信号,将对SMBHB起源的解释构成更大挑战。我们还识别出了更有可能产生可探测水平各向异性的SMBHB族群。该信息可与GWB的光谱特性结合使用,以表征SMBHB族群的特征。

英文摘要:

Several Pulsar Timing Array (PTA) collaborations have recently found evidence for a gravitational wave background (GWB) permeating our galaxy. The origin of this background is still unknown. Indeed, while the gravitational wave emission from inspiraling supermassive black hole binaries (SMBHB) is the primary candidate for its origin, several cosmological sources have also been proposed. One distinctive feature of SMBHB-generated backgrounds is the presence of GWB anisotropies stemming from the binaries distribution in the local Universe. However, none of the anisotropy searches performed to date reported a detection. In this work, we show that the lack of anisotropy detection is not currently in tension with a SMBHB origin of the background. We accomplish this by calculating the anisotropy detection probability of present and future PTAs. We find that a PTA with the noise characteristics of the NANOGrav 15-year data set had only a $~2\%-11\%$ probability of detecting SMBHB-generated anisotropies, depending on the properties of the SMBHB population. However, we estimate that for the IPTA DR3 data set these probabilities will increase to $~4\%-28\%$, putting more pressure on the SMBHB interpretation in case of a null detection. We also identify SMBHB populations that are more likely to produce detectable levels of anisotropies. This information could be used together with the spectral properties of the GWB to characterize the SMBHB population.

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