640 research outputs found
Resonant recoil in extreme mass ratio binary black hole mergers
The inspiral and merger of a binary black hole system generally leads to an
asymmetric distribution of emitted radiation, and hence a recoil of the remnant
black hole directed opposite to the net linear momentum radiated. The recoil
velocity is generally largest for comparable mass black holes and particular
spin configurations, and approaches zero in the extreme mass ratio limit. It is
generally believed that for extreme mass ratios eta<<1, the scaling of the
recoil velocity is V {\propto} eta^2, where the proportionality coefficient
depends on the spin of the larger hole and the geometry of the system (e.g.
orbital inclination). Here we show that for low but nonzero inclination
prograde orbits and very rapidly spinning large holes (spin parameter
a*>0.9678) the inspiralling binary can pass through resonances where the
orbit-averaged radiation-reaction force is nonzero. These resonance crossings
lead to a new contribution to the kick, V {\propto} eta^{3/2}. For these
configurations and sufficiently extreme mass ratios, this resonant recoil is
dominant. While it seems doubtful that the resonant recoil will be
astrophysically significant, its existence suggests caution when extrapolating
the results of numerical kick results to extreme mass ratios and near-maximal
spins.Comment: fixed references; matches PRD accepted version (minor revision); 9
pages, 2 figure
Binary black hole merger in the extreme-mass-ratio limit: a multipolar analysis
Building up on previous work, we present a new calculation of the
gravitational wave (GW) emission generated during the transition from
quasi-circular inspiral to plunge, merger and ringdown by a binary system of
nonspinning black holes, of masses and , in the extreme mass ratio
limit, . The relative dynamics of the system is computed
{\it without making any adiabatic approximation} by using an effective one body
(EOB) description, namely by representing the binary by an effective particle
of mass moving in a (quasi-)Schwarzschild background of
mass and submitted to an \O(\nu) 5PN-resummed analytical
radiation reaction force, with . The gravitational wave emission is
calculated via a multipolar Regge-Wheeler-Zerilli type perturbative approach
(valid in the limit ). We consider three mass ratios,
,and we compute the multipolar waveform up to
. We estimate energy and angular momentum losses during the
quasi-universal and quasi-geodesic part of the plunge phase and we analyze the
structure of the ringdown. We calculate the gravitational recoil, or "kick",
imparted to the merger remnant by the gravitational wave emission and we
emphasize the importance of higher multipoles to get a final value of the
recoil . We finally show that there is an {\it excellent
fractional agreement} () (even during the plunge) between the 5PN
EOB analytically-resummed radiation reaction flux and the numerically computed
gravitational wave angular momentum flux. This is a further confirmation of the
aptitude of the EOB formalism to accurately model extreme-mass-ratio inspirals,
as needed for the future space-based LISA gravitational wave detector.Comment: 20 pages, 12 figures. Version published in Phys. Rev.
Gravitational Radiation from Plunging Orbits - Perturbative Study -
Numerical relativity has recently yielded a plethora of results about kicks
from spinning mergers which has, in turn, vastly increased our knowledge about
the spin interactions of black hole systems. In this work we use black hole
perturbation theory to calculate accurately the gravitational waves emanating
from the end of the plunging stage of an extreme mass ratio merger in order to
further understand this phenomenon. This study focuses primarily on spin
induced effects with emphasis on the maximally spinning limit and the
identification of possible causes of generic behavior.
We find that gravitational waves emitted during the plunging phase exhibit
damped oscillatory behavior, corresponding to a coherent excitation of
quasi-normal modes by the test particle. This feature is universal in the sense
that the frequencies and damping time do not depend on the orbital parameters
of the plunging particle. Furthermore, the observed frequencies are distinct
from those associated with the usual free quasi-normal ringing. Our calculation
suggests that a maximum in radiated energy and momentum occurs at spin
parameters equal to and , respectively for the plunge
stage of a polar orbit. The dependence of linear momentum emission on the angle
at which a polar orbit impacts the horizon is quantified. One of the advantages
of the perturbation approach adopted here is that insight into the actual
mechanism of radiation emission and its relationship to black hole ringing is
obtained by carefully identifying the dominant terms in the expansions used
The effect of gravitational-wave recoil on the demography of massive black holes
The coalescence of massive black hole (MBH) binaries following galaxy mergers
is one of the main sources of low-frequency gravitational radiation. A
higher-order relativistic phenomenon, the recoil as a result of the non-zero
net linear momentum carried away by gravitational waves, may have interesting
consequences for the demography of MBHs at the centers of galaxies. We study
the dynamics of recoiling MBHs and its observational consequences. The
``gravitational rocket'' may: i) deplete MBHs from late-type spirals, dwarf
galaxies, and stellar clusters; ii) produce off-nuclear quasars, including
unusual radio morphologies during the recoil of a radio-loud source; and iii)
give rise to a population of interstellar and intergalactic MBHs.Comment: emulateapj, 5 pages, 2 figures, to appear in the ApJ Letter
Supermassive recoil velocities for binary black-hole mergers with antialigned spins
Recent calculations of the recoil velocity in binary black hole mergers have
found the kick velocity to be of the order of a few hundred km/s in the case of
non-spinning binaries and about km/s in the case of spinning
configurations, and have lead to predictions of a maximum kick of up to km/s. We test these predictions and demonstrate that kick velocities of at
least km/s are possible for equal-mass binaries with anti-aligned spins
in the orbital plane. Kicks of that magnitude are likely to have significant
repercussions for models of black-hole formation, the population of
intergalactic black holes and the structure of host galaxies.Comment: Final version, published by Phys. Rev. Lett.; title changed according
to suggestion of PRL; note added after preparation of manuscrip
Binary Black Holes: Spin Dynamics and Gravitational Recoil
We present a study of spinning black hole binaries focusing on the spin
dynamics of the individual black holes as well as on the gravitational recoil
acquired by the black hole produced by the merger. We consider two series of
initial spin orientations away from the binary orbital plane. In one of the
series, the spins are anti-aligned; for the second series, one of the spins
points away from the binary along the line separating the black holes. We find
a remarkable agreement between the spin dynamics predicted at 2nd
post-Newtonian order and those from numerical relativity. For each
configuration, we compute the kick of the final black hole. We use the kick
estimates from the series with anti-aligned spins to fit the parameters in the
\KKF{,} and verify that the recoil along the direction of the orbital angular
momentum is and on the orbital plane ,
with the angle between the spin directions and the orbital angular
momentum. We also find that the black hole spins can be well estimated by
evaluating the isolated horizon spin on spheres of constant coordinate radius.Comment: 15 pages, 10 figures, replaced with version accepted for publication
in PR
Gravitational recoil from spinning binary black hole mergers
The inspiral and merger of binary black holes will likely involve black holes
with both unequal masses and arbitrary spins. The gravitational radiation
emitted by these binaries will carry angular as well as linear momentum. A net
flux of emitted linear momentum implies that the black hole produced by the
merger will experience a recoil or kick. Previous studies have focused on the
recoil velocity from unequal mass, non-spinning binaries. We present results
from simulations of equal mass but spinning black hole binaries and show how a
significant gravitational recoil can also be obtained in these situations. We
consider the case of black holes with opposite spins of magnitude
aligned/anti-aligned with the orbital angular momentum, with the
dimensionless spin parameters of the individual holes. For the initial setups
under consideration, we find a recoil velocity of V = 475 \KMS a.
Supermassive black hole mergers producing kicks of this magnitude could result
in the ejection from the cores of dwarf galaxies of the final hole produced by
the collision.Comment: 8 pages, 8 figures, replaced with version accepted for publication in
Ap
How black holes get their kicks: Gravitational radiation recoil revisited
Gravitational waves from the coalescence of binary black holes carry away
linear momentum, causing center of mass recoil. This "radiation rocket" effect
has important implications for systems with escape speeds of order the recoil
velocity. We revisit this problem using black hole perturbation theory,
treating the binary as a test mass spiraling into a spinning hole. For extreme
mass ratios (q = m1/m2 << 1) we compute the recoil for the slow inspiral epoch
of binary coalescence very accurately; these results can be extrapolated to q ~
0.4 with modest accuracy. Although the recoil from the final plunge contributes
significantly to the final recoil, we are only able to make crude estimates of
its magnitude. We find that the recoil can easily reach ~ 100-200 km/s, but
most likely does not exceed ~ 500 km/s. Though much lower than previous
estimates, this recoil is large enough to have important astrophysical
consequences. These include the ejection of black holes from globular clusters,
dwarf galaxies, and high-redshift dark matter halos.Comment: 4 pages, 2 figures, emulateapj style; minor changes made; accepted to
ApJ Letter
Recoil velocity at 2PN order for spinning black hole binaries
We compute the flux of linear momentum carried by gravitational waves emitted
from spinning binary black holes at 2PN order for generic orbits. In particular
we provide explicit expressions of three new types of terms, namely
next-to-leading order spin-orbit terms at 1.5 PN order, spin-orbit tail terms
at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to
quasi-circular orbits, we integrate the linear momentum flux over time to
obtain the recoil velocity as function of orbital frequency. We find that in
the so-called superkick configuration the higher-order spin corrections can
increase the recoil velocity up to about a factor 3 with respect to the
leading-order PN prediction. Furthermore, we provide expressions valid for
generic orbits, and accurate at 2PN order, for the energy and angular momentum
carried by gravitational waves emitted from spinning binary black holes.
Specializing to quasi-circular orbits we compute the spin-spin terms at 2PN
order in the expression for the evolution of the orbital frequency and found
agreement with Mik\'oczi, Vas\'uth and Gergely. We also verified that in the
limit of extreme mass ratio our expressions for the energy and angular momentum
fluxes match the ones of Tagoshi, Shibata, Tanaka and Sasaki obtained in the
context of black hole perturbation theory.Comment: 28 pages (PRD format), 1 figure, reference added, version published
in PRD, except that the PRD version contains a sign error: the sign of the
RHS of Eqs.(4.26) and (4.27) is wrong; it has been corrected in this
replacemen
Retaining Black Holes with Very Large Recoil Velocities
Recent numerical simulations of binary black hole mergers show the
possibility of producing very large recoil velocities (> 3000 km/s). Kicks of
this magnitude should be sufficient to eject the final black hole from
virtually any galactic potential. This result has been seen as a potential
contradiction with observations of supermassive black holes residing in the
centers of most galaxies in the local universe. Using an extremely simplified
merger tree model, we show that, even in the limit of very large ejection
probability, after a small number of merger generations there should still be
an appreciable fraction (>50%) of galaxies with supermassive black holes today.
We go on to argue that the inclusion of more realistic physics ingredients in
the merger model should systematically increase this retention fraction,
helping to resolve a potential conflict between theory and observation. Lastly,
we develop a more realistic Monte Carlo model to confirm the qualitative
arguments and estimate occupation fractions as a function of the central
galactic velocity dispersion.Comment: 6 pages, 3 figures; Comments welcom
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