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arXiv 2306.02440astro-ph.GAastro-ph.COhep-ph
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微引力透镜黑洞阴影

Microlensing Black Hole Shadows

Himanshu Verma, Joseph Silk

AI总结:

本文研究居间致密天体对EHT黑洞阴影的微透镜效应,量化其位移、约50%尺寸增强和最高约8%的不对称性,并指出月球与L₂基线及Sgr A*监测的探测前景。

摘要:

本文对事件视界望远镜(Event Horizon Telescope,EHT)所成像的黑洞阴影受到居间致密天体引力微透镜作用的情况进行了详细分析。我们展示了阴影的中心、大小和形状如何依赖于爱因斯坦角相对于真实/未受透镜作用阴影尺寸的关系,以及透镜位置如何因微透镜效应影响黑洞阴影的位移、大小和不对称性。假设超大质量黑洞(supermassive black hole,SMBH)投下圆形的真实阴影,微透镜可产生最高约8%的不对称性,这是由SMBH自转及其相对于我们的倾角所造成不对称性的两倍。此外,阴影尺寸可增强至真实阴影的约50%。目前,EHT的地面基线缺乏探测阴影中微透镜特征所需的分辨率。然而,EHT未来的扩展,包括位于月球和L₂的天基基线,可能使微透镜事件的探测成为可能。对于Sgr A*,在透镜质量约为M⊙、恒星来自核球和恒星盘的情况下,每年0.0014次的事件率使得即使利用天基基线,微透镜现象也难以观测。尽管如此,银河系中心秒差距内存在由2万个恒星级黑洞组成的星团——预计由作用于落入恒星团的动力学摩擦产生——会显著提高事件率。因此,持续监测Sgr A*的阴影可为银河系中心周围的致密天体族群提供新的认识。

英文摘要:

A detailed analysis is presented of gravitational microlensing by intervening compact objects of the black hole shadows imaged by the Event Horizon Telescope (EHT). We show how the center, size, and shape of the shadow depend on the Einstein angle relative to the true/unlensed shadow size, and how the location of the lens affects the shift, size, and asymmetry of the black hole shadow due to microlensing. Assuming a supermassive black hole (SMBH) casts a circular-shaped true shadow, microlensing can create an asymmetry of up to approximately 8\%, which is twice the asymmetry caused by the SMBH's spin and its tilt relative to us. Furthermore, the size can be enhanced by $\sim$50\% of the true shadow. Currently, the terrestrial baselines of EHT lack the resolution to detect microlensing signatures in the shadows. However, future expansions of EHT, including space-based baselines at the Moon and L$_2$, could potentially enable the detection of microlensing events. For Sgr A$^*$, an event rate of 0.0014 per year makes the microlensing phenomena difficult to observe even with space-based baselines for the stellar population in the stellar bulge and stellar disk for lens masses $\sim M_\odot$. Nonetheless, the presence of a cluster of 20,000 stellar-mass black holes in the central parsec of the Milky Way, expected to arise from dynamical friction acting on infalling stellar clusters, significantly boosts the event rate. Hence, continuously monitoring the shadow of Sgr A$^*$ could offer novel insights into the compact object population surrounding the Galactic Center.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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