1,721,167 research outputs found
Low-frequency gravitational radiation from coalescing massive black hole binaries in hierarchical cosmologies
No full textWe compute the expected low-frequency gravitational wave signal from coalescing massive black hole (MBH) binaries at the center of galaxies in a hierarchical structure formation scenario in which seed holes of intermediate mass form far up in the dark halo "merger tree." The merger history of dark matter halos and associated MBHs is followed via cosmological Monte Carlo realizations of the merger hierarchy from redshift z = 20 to the present in a ΛCDM cosmology. MBHs get incorporated through halo mergers into larger and larger structures, sink to the center because of dynamical friction against the dark matter background, accrete cold material in the merger remnant, and form MBH binary systems. Stellar dynamical (three-body) interactions cause the hardening of the binary at large separations, while gravitational wave emission takes over at small radii and leads to the final coalescence of the pair. A simple scheme is applied in which the "loss cone" is constantly refilled and a constant stellar density core forms because of the ejection of stars by the shrinking binary. The integrated emission from inspiraling MBH binaries at all redshifts is computed in the quadrupole approximation and results in a gravitational wave background (GWB) with a well-defined shape that reflects the different mechanisms driving the late orbital evolution. The characteristic strain spectrum has the standard hc(f) f-2/3 behavior only in the range f = 10-9 to 10-6 Hz. At lower frequencies the orbital decay of MBH binaries is driven by the ejection of background stars ("gravitational slingshot"), and the strain amplitude increases with frequency, hc(f) f. In this range the GWB is dominated by 109-1010 M MBH pairs coalescing at 0 z 2. At higher frequencies, f > 10-6 Hz, the strain amplitude, as steep as hc(f) f-1.3, is shaped by the convolution of last stable circular orbit emission by lighter binaries (102-107 M) populating galaxy halos at all redshifts. We discuss the observability of inspiraling MBH binaries by a low-frequency gravitational wave experiment such as the planned Laser Interferometer Space Antenna (LISA). Over a 3 yr observing period LISA should resolve this GWB into discrete sources, detecting 60 (250) individual events above an S/N = 5 (S/N = 1) confidence level
Interaction of massive black hole binaries with their stellar environment. I. Ejection of hypervelocity stars
No full textWe use full three-body scattering experiments to study the ejection of hypervelocity stars (HVSs) by massive black hole binaries (MBHBs) at the centers of galaxies. Ambient stars drawn from a Maxwellian distribution unbound to the binary are expelled by the gravitational slingshot. Accurate measurements of thermally averaged hardening, mass ejection, and eccentricity growth rates (H, J, and K ) for MBHBs in a fixed stellar background are obtained by numerical orbit integration from initial conditions determined by Monte Carlo techniques. Three-body interactions create a subpopulation of HVSs on nearly radial orbits, with a spatial distribution that is initially highly flattened in the inspiral plane of the MBHB, but becomes more isotropic with decreasing binary separation. The degree of anisotropy is smaller for unequal mass binaries and larger for stars with higher kick velocities. Eccentric MBHBs produce a more prominent tail of high-velocity stars and break planar symmetry, ejecting HVSs along a broad jet perpendicular to the semimajor axis. The jet two-sidedness decreases with increasing binary mass ratio, while the jet opening angle increases with decreasing kick velocity and orbital separation. The detection of a numerous population of HVSs in the halo of the Milky Way by the next generation of large astrometric surveys such as Gaia may provide a unique signature of the history, nature, and environment of the MBH at the Galactic center
Ejection of hypervelocity binary stars by a black hole of intermediate mass orbiting Sgr A
No full textInteraction of Massive Black Hole Binaries with Their Stellar Environment. III. Scattering of Bound Stars
No full textLISA detection of massive black hole binaries: imprint of seed populations and extreme recoils
No full textOn the search of electromagnetic cosmological counterparts to coalescences of massive black hole binaries
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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