近日，美国麻省理工学院的Megan Masterson及其研究团队取得一项新进展。经过不懈努力，他们发现超大质量黑洞最内层轨道附近的毫赫兹振荡。相关研究成果已于2025年2月5日在国际权威学术期刊《自然》上发表。

该研究团队报道了在一个活跃吸积的超大质量黑洞（SMBH）1ES1927+654中发现的一个高度显著的毫赫兹准周期性振荡（QPO）。该黑洞自2018年起经历了一次重大的光学、紫外和X射线爆发。2022年，研究人员检测到了这个QPO，其周期约为18分钟，对应于小于10个引力半径范围内的相干运动，这比典型的准周期性爆发更靠近超大质量黑洞。在两年的时间内，该周期减速演变（变化率大于零），减少至7.1分钟。

据他们所知，这种演变在超大质量黑洞QPO或恒星质量黑洞的高频QPO中从未被观测到。那些假设恒星质量伴星轨道衰变的模型，在没有稳定的物质转移来抵消角动量损失的情况下，难以解释这一周期演变；同时，由于缺乏与恒星质量黑洞QPO的直接类比，许多不稳定性模型也无法解释1ES1927+654中QPO的所有观测特性。未来的X射线监测将对这些模型进行检验，如果这是一个恒星质量的轨道天体，那么激光干涉空间天线（LISA）应该能够检测到其低频引力波辐射。

据悉，近期时域巡天观测的发现挑战了人们对物质如何被超大质量黑洞（SMBH）吸积的认知。超大质量黑洞周围短时间内重复发生的事件频率增加，包括最近发现的准周期性爆发，使得人们对超大质量黑洞周围的恒星质量伴星以及毫赫兹频率引力波事件的前身产生了更浓厚的兴趣。

附：英文原文

Title: Millihertz oscillations near the innermost orbit of a supermassive black hole

Author: Masterson, Megan, Kara, Erin, Panagiotou, Christos, Alston, William N., Chakraborty, Joheen, Burdge, Kevin, Ricci, Claudio, Laha, Sibasish, Arcavi, Iair, Arcodia, Riccardo, Cenko, S. Bradley, Fabian, Andrew C., Garca, Javier A., Giustini, Margherita, Ingram, Adam, Kosec, Peter, Loewenstein, Michael, Meyer, Eileen T., Miniutti, Giovanni, Pinto, Ciro, Remillard, Ronald A., Sadaula, Dev R., Shuvo, Onic I., Trakhtenbrot, Benny, Wang, Jingyi

Issue&Volume: 2025-02-05

Abstract: Recent discoveries from time-domain surveys are defying our expectations for how matter accretes onto supermassive black holes (SMBHs). The increased rate of short-timescale, repetitive events around SMBHs, including the recently discovered quasi-periodic eruptions, are garnering further interest in stellar-mass companions around SMBHs and the progenitors to millihertz-frequency gravitational-wave events. Here we report the discovery of a highly significant millihertz quasi-periodic oscillation (QPO) in an actively accreting SMBH, 1ES1927+654, which underwent a major optical, ultraviolet and X-ray outburst beginning in 2018. The QPO was detected in 2022 with a roughly 18-minute period, corresponding to coherent motion on a scale of less than 10 gravitational radii, much closer to the SMBH than typical quasi-periodic eruptions. The period decreased to 7.1minutes over 2years with a decelerating period evolution (greater than zero). To our knowledge, this evolution has never been seen in SMBH QPOs or high-frequency QPOs in stellar-mass black holes. Models invoking orbital decay of a stellar-mass companion struggle to explain the period evolution without stable mass transfer to offset angular-momentum losses, and the lack of a direct analogue to stellar-mass black-hole QPOs means that many instability models cannot explain all of the observed properties of the QPO in 1ES1927+654. Future X-ray monitoring will test these models, and if it is a stellar-mass orbiter, the Laser Interferometer Space Antenna (LISA) should detect its low-frequency gravitational-wave emission.

DOI: 10.1038/s41586-024-08385-x

Source: https://www.nature.com/articles/s41586-024-08385-x