A Compact Supermassive Binary Black Hole System

Abstract

We report on the discovery of a supermassive binary black hole system in the radio galaxy 0402+379, with a projected separation between the two black holes of just 7.3 pc. This is the closest black hole pair yet found by more than two orders of magnitude. These results are based upon recent multi-frequency observations using the Very Long Baseline Array (VLBA) which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of 0402+379. Multiepoch observations from the VLBA also provide constraints on the total mass and dynamics of the system. Low spectral resolution spectroscopy using the Hobby-Eberly Telescope indicates two velocity systems with a combined mass of the two black holes of ∼ 1.5 × 10 8 M ⊙ . The two nuclei appear stationary while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hot spots. The discovery of this system has implications for the number of close binary black holes that might be sources of gravitational radiation. Green Bank Telescope observations at 22 GHz to search for water masers in this interesting system are also presented.

Dynamics of galaxy cores and supermassive black holes

“…A handful of galaxies exhibit two active nuclei with separations as small as ∼ 1 kpc (Komossa 2003, Ballo et al 2004, Hudson et al 2006, much greater however than the parsec-scale separations that characterize true binaries. Very recently (Rodriguez et al 2006), VLBA observations of an elliptical galaxy at z = 0.055 with two compact central radio sources were used to infer the presence of the first, true binary SBH; the projected separation is only ∼ 7 pc and the inferred total mass is ∼ 1.5 × 10 8 M ⊙ . A binary SBH with a ≈ a h (Equation 15) contains a fraction ∼ (M 1 + M 2 )/M gal ≈ 10 −3 of the total gravitational energy of its host galaxy, and such a large binding energy implies a significant change in the distribution of stars, gas or dark matter at the center of the galaxy when the binary forms.…”

“…It is also a "problem" in the sense that many circumstantial lines of evidence suggest that SBH binaries do efficiently coalesce. (a) Only one, reasonably compelling case for a true binary SBH exists (Rodriguez et al 2006), even though binaries with the same projected separation (∼ 7 pc, which is the expected stalling radius for a M 12 ≈ 10 9 M ⊙ binary; see Table 1) could be easily resolved in many other galaxies by radio interferometry. (b) Jets in the great majority of radio galaxies do not show the wiggles expected if the SBH hosting the accretion disk were orbiting or precessing.…”

Black-hole binaries, gravitational waves, and numerical relativity

“…Since essentially all galaxies are believed to contain an MBH at the center and to undergo a merger with another galaxy at least once during the history of the Universe, MBH binaries can arise when their host galaxies merge (Begelman et al, 1980); see also Djorgovski et al (2008) and references therein. However, due to the vast cosmic distances involved, and the small angular separations on the sky expected for MBH binaries, only a few candidates are currently known through electromagnetic observations (Komossa, 2003;Komossa et al, 2003;Rodriguez et al, 2006). When they form, MBH bina-ries typically have relatively wide separations, and the gravitational radiation they emit is very weak and insufficient to cause the binary to coalesce within the age of the Universe.…”

A close-pair binary in a distant triple supermassive black hole system

“…To date, there are very few confirmed dual/binary AGN, despite the expectations from our understanding of hierarchical structure formation through galaxy merging, combined with the observational evidence that every massive galaxy hosts a central SMBH 21 . Of the dual/binary AGN with direct imaging confirmation, only three have sub-kpc projected separations and these systems are all below z 0.06 10,22,23 . In addition to these, there are a handful of candidate close-pair binaries based on light curve analyses, double-peaked broad lines and radio jet morphology 18,24,25 , but these are not spatially resolved by current instruments.…”

“…There are four known triple black hole systems [5][6][7][8] , with the closest pair being 2.4 kiloparsecs apart (the third component is more distant at 3 kiloparsecs) 7 , which is far from the gravitational sphere of influence of a black hole with mass ∼10 9 M (about 100 parsecs). Previous searches for compact black hole systems concluded that they were rare 9 , with the tightest binary system having a separation of 7 parsecs 10 . Here we report observations of a triple black hole system at redshift z=0.…”