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We investigate the time-varying electromagnetic emission of a low-mass-ratio supermassive black hole binary (SMBHB) embedded in a circumprimary disk, with a particular interest in variability of shocks driven by the binary. We perform a 2D,…

The observation of a population of massive black hole binaries (MBHBs) is key for our complete understanding of galaxy mergers and for the characterization of the expected gravitational waves (GWs) signal. However, MBHBs still remain…

We study the dynamics of a solar-type star orbiting around a black hole binary (BHB) in a nearly coplanar system. We present a novel effect that can prompt a growth and significant oscillations of the eccentricity of the stellar orbit when…

Here we present results from our spectroscopic follow-up of SDSS J2320+0024, a candidate binary supermassive black hole (SMBH) with a suspected sub-pc separation, identified by a 278-day periodicity observed in its multi-band optical light…

Close binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (Alpha Virginis) consisting…

Pulsar timing array (PTA) experiments are expected to detect nano-Hertz gravitational waves (GWs) emitted from individual inspiralling supermassive binary black holes (SMBBHs). The GW signals from a small fraction of these SMBBHs may be…

The couplings between supermassive black-hole binaries and their environments within galactic nuclei have been well studied as part of the search for solutions to the final parsec problem. The scattering of stars by the binary or the…

We present Hubble Space Telescope ultraviolet (UV) of 13 quasars at z<0.7, along with contemporaneous optical spectra from ground-based telescopes. The targets were selected to have broad H-beta emission lines with substantial velocity…

Supermassive black hole binaries (SMBHBs) at sub-parsec separations should be common in galactic nuclei, as a result of frequent galaxy mergers. Hydrodynamical simulations of circumbinary discs predict strong periodic modulation of the mass…

We present an analysis of the apsidal motion and light curve parameters of 54 never-before-studied galactic Algol-type binaries. This is the first analysis of such a large sample of eccentric eclipsing binaries in our Galaxy, and has…

The highly variable blazar OJ~287 is commonly discussed as an example of a binary black hole system. The 130 year long optical light curve is well explained by a model where the central body is a massive black hole of 18.35$\times$10$^9$…

We present long-term (2012-2022) optical monitoring of the candidate black hole X-ray binary Swift J1910.2-0546 with the Faulkes Telescopes and Las Cumbres Observatory (LCO) network. Following its initial bright 2012 outburst, we find that…

We consider the gravitational magnification of light for binary systems containing two compact objects: white dwarfs, a white dwarf and a neutron star or a white dwarf and a black hole. Light curves of the flares of the white dwarf caused…

We present Kepler and Swift observations of StHa 169 which is currently classified as a symbiotic binary. The Kepler light curve shows quasi periodic behaviour with a mean period of 34 d and an amplitude of a few percent. Using Swift data…

The eccentricity, periastron angle, orbital inclination, mass ratio, stellar temperatures and relative stellar radii of 12 eclipsing eccentric binaries were determined on the basis of Kepler data. The analysis of their out-of-eclipse…

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies characteristic of SPB stars. Seven of these stars also show a few weak, isolated high…

The Legacy Survey of Space and Time (LSST) is expected to observe up to ${\sim}100$ million quasars in the next decade. In this work, we show that it is possible to use such data to measure the characteristic frequency evolution of a…

Some pulsating stars are good clocks. When they are found in binary stars, the frequencies of their luminosity variations are modulated by the Doppler effect caused by orbital motion. For each pulsation frequency this manifests itself as a…

One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole system in their cores. Here we present an observational evidence for the first…

Apparently periodic optical variations of the luminous high-redshift (z=2.06) quasar PSO J334.2028+1.4075 led Liu et al. (2015) to interpret the variability as the orbital period of a binary supermassive black hole (SMBH) residing in a…