Close binary black hole in a radio-quiet quasar: a candidate of Nano-Hertz gravitational wave emitter

作     者：Feng, Hai-Cheng Liu, Hong-Tao Bai, Jin-Ming 

作者机构：Yunnan Observatories Chinese Academy of Sciences Kunming Yunnan650011 China University of Chinese Academy of Sciences Beijing100049 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming Yunnan650011 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China 

出 版 物：《Research Square》 (Research Square)

年 卷 期：2021年

核心收录：

主　　题：Gravity waves 

摘      要：Close supermassive binary black holes (SMBBHs) with separations less than ∼ 0.1 parsec are expected to be Nano-Hertz gravitational wave sources1. SMBBH systems should exhibit periodic variability2. However, periodic variability in radio-loud quasars may be interpreted with the jet model3. Here we report the detection of a robust periodic signal in the optical variability of the radio-quiet quasar PG 0923+201 with an observed period of 726.8 ± 4.7 days, obtained from the sinusoid-like light curve of a temporal baseline of about 9 years. This periodicity is probably from a close SMBBH with a total mass of 109.3 solar masses and a separation of ∼ 0.01 parsec, implying relativistic orbital speeds. Such a system has passed through the well-known final parsec problem of SMBBH systems4, and the Nano-Hertz gravitational wave radiation becomes significant. The ratio of the separation between these two black holes to the broad-line region size is ∼ 0.1. A close SMBBH is also suggested by this small ratio and the spectral properties of Balmer broad lines in this quasar. This radio-quiet quasar is a candidate emitter of Nano-Hertz gravitational waves at a frequency of about 30 Nano-Hertz. © 2021, CC BY.