It has been proposed that when the peaks of the broad emission lines in active galactic nuclei (AGNs) are significantly blueshifted or redshifted from the systemic velocity of the host galaxy, this could be a consequence of orbital motion of a supermassive blackhole binary (SMB) (Gaskell 1983). The AGN J1536+0441 (=SDSS J153636.22+044127.0) has recently been proposed as an example of this phenomenon (Boroson & Lauer 2009). It is proposed here instead that 1536+044 is an example of line emission from a disc. If this is correct, the lack of clear optical spectral evidence for close SMBs is significant and argues either that the merging of close SMBs is much faster than has generally been hitherto thought, or if the approach is slow, that when the separation of the binary is comparable to the size of the torus and broad-line region, the feeding of the black holes is disrupted.
The study of galaxy mergers and supermassive binary black holes (SMBBHs) is central to our understanding of the galaxy and black hole assembly and (co-)evolution at the epoch of structure formation and throughout cosmic history. Galaxy mergers are the sites of major accretion episodes, they power quasars, grow supermassive black holes (SMBHs), and drive SMBH-host scaling relations. The coalescing SMBBHs at their centers are the loudest sources of gravitational waves (GWs) in the universe, and the subsequent GW recoil has a variety of potential astrophysical implications which are still under e…
Composite profile of the Fe K$α$ spectral line emitted from a binary system of supermassive black holes
采用相对论性的超大质量黑洞吸积盘模型，基于Kerr度规的射线追踪方法，研究了双星系统中两个吸积盘围绕超大质量黑洞发射的复合Fe K $α$线的变化.我们假定这类双星的轨道近似为开普勒轨道，并模拟了不同轨道根数、吸积盘参数和组分质量比时的合成线形。结果表明，如果在某些SMBH双星的不同轨道相位的光谱中观测到这种复合Fe K $α$谱线轮廓，可以用来约束这类SMBH双星的轨道和一些性质.
Supermassive black hole binaries (SMBHs) are expected to result from galaxy mergers, and thus are natural byproducts (and probes) of hierarchical structure formation in the Universe. They are also the primary expected source of low-frequency gravitational wave emission. We search for binary BHs using time-variable velocity shifts in broad Mg II emission lines of quasars with multi-epoch observations. First, we inspect velocity shifts of the binary SMBH candidates identified in Ju et al. (2013), using SDSS spectra with an additional epoch of data that lengthens the typical baseline to ~10 yr. W…
We study the dynamical evolution of supermassive black holes, in the late stage of galaxy mergers, from kpc to pc scales. In particular, we capture the formation of the binary, a necessary step before the final coalescence, and trace back the main processes causing the decay of the orbit. We use hydrodynamical simulations of galaxy mergers with different resolutions, from $20\,\rm pc$ down to $1\,\rm pc$, in order to study the effects of the resolution on our results, remove numerical effects, and assess that resolving the influence radius of the orbiting black hole is a minimum condition to f…
Effects of dark dipole radiation on eccentric supermassive black hole binary inspirals
School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS)（中国科学院大学天文与空间科学学院）；School of Physics, Nanjing University（南京大学物理学院）
Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems will modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrain the characteristic amplitude of this background, $A_{\rm c,yr}$, to be < $1.0\times10^{-15}$ with 95% confidence. This limit excludes predicted ranges for $A_{\rm c,yr}$ from current models with 91-99.7% probability. We conclude that binary evoluti…
We present an analytic model to describe the supermassive black hole binary (SMBHB) merger rate in the Universe with astrophysical observables: galaxy stellar mass function, pair fraction, merger timescale and black hole - host galaxy relations. We construct observational priors and compute the allowed range of the characteristic spectrum $h_c$ of the gravitational wave background (GWB) to be $10^{-16}<h_c<10^{-15}$ at a frequency of $f=1/{\rm yr}$. We exploit our parametrization to tackle the problem of astrophysical inference from Pulsar Timing Array (PTA) observations. We simulate a series …
We investigate the evolution of supermassive binary black holes (BBHs) in galaxies with realistic property distributions and the gravitational-wave (GW) radiation from the cosmic population of these BBHs. We incorporate a comprehensive treatment of the dynamical interactions of the BBHs with their environments by including the effects of galaxy triaxial shapes and inner stellar distributions, and generate a large number of BBH evolution tracks. By combining these BBH evolution tracks, galaxy mass functions, galaxy merger rates, and supermassive black hole-host galaxy relations into our model, …
Given the stellar density near the galactic center, close encounters between compact object binaries and the supermassive black hole are a plausible occurrence. We present results from a numerical study of close to 13 million such encounters. Consistent with previous studies, we corroborate that, for binary systems tidally disrupted by the black hole, the component of the binary remaining bound to the hole has eccentricity ~ 0.97 and circularizes dramatically by the time it enters the classical LISA band. Our results also show that the population of surviving binaries merits attention. These b…
We report periodic oscillations in the 15-year long optical light curve of the gravitationally lensed quasar QJ0158-4325. The signal is enhanced during a high magnification microlensing event undergone by the fainter lensed image of the quasar, between 2003 and 2010. We measure a period of $P_{o}=172.6\pm0.9$ days. We explore four scenarios to explain the origin of the periodicity: 1- the high magnification microlensing event is due to a binary star in the lensing galaxy, 2- QJ0158-4325 contains a massive binary black hole system in its final dynamical stage before merging, 3- the quasar accre…
The properties of the first continuous gravitational waves: Optimizing pulsar timing observations for supermassive black hole binary detection
School of Physics, The University of Melbourne（墨尔本大学物理学院）；OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery（引力波发现ARC卓越中心）；School of Physics and Astronomy, Monash University（蒙纳士大学物理与天文学院）
