Skip to main content

A Population of Short-Period Variable Quasars as Supermassive Black Hole Binary Candidates


Image: Quasar Pair Captured in Galaxy Collision. Credits: X-ray: NASA/CXC/SAO/P. Green et al. Optical: Carnegie Obs./Magellan/W. Baade Telescope/J.S. Mulchaey et al.

Strong observational evidence suggests that every massive galaxy hosts a supermassive black hole in its nucleus. The central black hole (BH) is an important component of the galaxy, since the BH mass is correlated with the global properties of the host galaxy, e.g., dispersion velocity, bulge luminosity, or bulge mass.

Moreover, hierarchical models of structure formation predict that galaxies merge frequently, which naturally leads to the the formation of Supermassive black hole binaries (SMBHBs). Following the merger, the BHs rapidly sink towards the centre of the common gravitational potential, under the effect of dynamical friction, and form a bound Keplerian binary. Subsequently, the binary orbit decays, as the BHs expel nearby stars in close three-body interactions, and/or as they interact with a gaseous circumbinary disc. At close separations, the binary is driven to coalescence by the emission of gravitational radiation.

Hydrodynamical simulations of circumbinary discs predict strong periodic modulation of the mass accretion rate on time-scales comparable to the orbital period of the binary. As a result, SMBHBs may be recognized by the periodic modulation of their brightness.

In a recent paper (Charisi et al. 2016) the authors conducted a statistical search for periodic variability in a sample of 35,383 spectroscopically confirmed quasars in the photometric database of the Palomar Transient Factory (PTF).

They assessed the significance of their findings by modeling each individual quasar's variability as a damped random walk (DRW). They identified 33 quasars with significant periodicity beyond the DRW model, typically with short periods of a few hundred days.

Assuming that the observed periods correspond to the redshifted orbital periods of SMBHBs, they conclude that their findings are consistent with a population of unequal-mass SMBHBs, with a typical mass ratio as low as q = M2/M1 ~ 0.01.

  • Charisi et al. 2016 (preprint) - A Population of Short-Period Variable Quasars from PFT as Supermassive Black Hole Binary Candidates - (arXiv)
Etichette:

Comments

Post a Comment

Popular posts from this blog

ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).
Post a Comment
Read more

CONSTRAINTS ON THE LOCATION OF A POSSIBLE 9TH PLANET

Image: The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Such an orbital alignment can only be maintained by some outside force, Batygin and Brown say. Their paper argues that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Credit: Caltech The astronomers have noticed some of the dwarf planets and other small, icy objects tend to follow orbits that cluster together. To explain the unusual distribution of these Kuiper Belt objects, several authors have advocated the existence of a superEarth planet in the outer solar system ( planet Nine or planet X ).
1 comment
Read more

RADIATIVE CLEARING OF PROTOPLANETARY DISCS

Image: protoplanetary disc surrounding the young star HL Tauri, a very young T Tauri star in the constellation Taurus, approximately 450 light-years (140 pc) from Earth in the Taurus Molecular Cloud. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO) T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence. Their central temperatures are too low for hydrogen fusion. Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years. Roughly half of T Tauri stars have circumstellar disks, which in this case are called protoplanetary discs because they are probably the progenitors of planetary systems like the Solar System.
Post a Comment
Read more