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Recent observations indicate that many if not all galaxies host massive central black holes (BHs). In this paper we explore the influence of supermassive binary black holes (SMBBHs) on their actions as gravitational lenses. When lenses are…
We present a systematic search for periodically varying quasar and supermassive black hole binary (SMBHB) candidates in the Pan-STARRS1 Medium Deep Survey. From $\sim9,000$ color-selected quasars in a $\sim50$ deg$^{2}$ sky area, we…
The localization of stellar-mass binary black hole mergers using gravitational waves is critical in understanding the properties of the binaries' host galaxies, observing possible electromagnetic emission from the mergers, or using them as…
Variability of active galactic nuclei is not well understood. One possible explanation is existence of supermassive binary black holes (SMBBH) in their centres. It is expected that major mergers are common in the Universe. It is expected…
Stellar companion of a black hole orbiting in an eccentric orbit will experience modulating tidal force with a periodicity same as that of the orbital period. This, in turn, would modulate accretion rates, and the seed photon flux which are…
Some of the theoretical challenges posed by the general relativistic description of binary systems of compact objects (neutron stars or black holes) are reviewed. We recall the various ways one can use the theory of the motion, and of the…
Supermassive black hole (BH) binaries are thought to produce self-lensing flares (SLF) when the two BHs are aligned with the line-of-sight. If the binary orbit is observed nearly edge-on, we find a distinct feature in the light curve…
Gravitational-wave (GW) observations of binary black holes offer the best probes of the relativistic, strong-field regime of gravity. Gravitational radiation, in the leading order is quadrupolar. However, non-quadrupole (higher-order) modes…
It was recently suggested that the merger of $\sim30\,M_\odot$ primordial black holes (PBHs) may provide a significant number of events in gravitational-wave observatories over the next decade, if they make up an appreciable fraction of the…
We study spectral and time variability of accreting massive black hole binaries (MBHBs) at milli-pc separations surrounded by a geometrically thin circumbinary disc. We present the first computed spectral energy distribution (SED) and light…
Pairs of supermassive black holes (SMBHs) at different stages are natural results of galaxy mergers in the hierarchical framework of galaxy formation and evolution. However, identifications of close binaries of SMBHs (CB-SMBHs) with…
Gravitational lensing in the wave-optics regime imprints characteristic frequency-dependent amplitude and phase modulations on gravitational-wave (GW) signals, yet to be detected by ground-based interferometers. Similar modulations may also…
Pulsar timing is a promising technique for detecting low frequency sources of gravitational waves. Historically the focus has been on the detection of diffuse stochastic backgrounds, such as those formed from the superposition of weak…
Coalescence of binary supermassive black holes (SBHs) would constitute the strongest sources of gravitational waves to be observed by LISA. While the formation of binary SBHs during galaxy mergers is almost inevitable, coalescence requires…
A populations of stellar mass black hole binaries may exist in globular clusters. The dynamics of globular cluster evolution imply that there may be at most one black hole binary is a globular cluster. The population of binaries are…
Massive black-hole binaries (MBHBs) are thought to be the main source of gravitational waves (GWs) in the low-frequency domain surveyed by ongoing and forthcoming Pulsar Timing Array campaigns and future space-borne missions, such as {\it…
We study the dynamical evolution of eccentric massive black hole binaries (MBHBs) interacting with unbound stars by means of an extensive set of three body scattering experiments. Compared to previous studies, we extend the investigation…
We present the result of $N$-body simulations of dynamical evolution of triple massive blackhole (BH) systems in galactic nuclei. We found that in most cases two of the three BHs merge through gravitational wave (GW) radiation in the…
Binary supermassive black hole (SMBH) systems result from galaxy mergers, and will eventually coalesce due to gravitational wave (GW) emission if the binary separation can be reduced to $\lesssim 0.1$ pc by other mechanisms. Here, we…
Supermassive black holes (SMBHs) found in the centers of many galaxies have been recognized to play a fundamental active role in the cosmological structure formation process. In hierarchical formation scenarios, SMBHs are expected to form…