402 research outputs found
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
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
Gravitational Recoil during Binary Black Hole Coalescence using the Effective One Body Approach
Using the Effective One Body approach, that includes nonperturbative resummed
estimates for the damping and conservative parts of the compact binary
dynamics, we compute the recoil during the late inspiral and the subsequent
plunge of non-spinning black holes of comparable masses moving in
quasi-circular orbits. Further, using a prescription that smoothly connects the
plunge phase to a perturbed single black hole, we obtain an estimate for the
total recoil associated with the binary black hole coalescence. We show that
the crucial physical feature which determines the magnitude of the terminal
recoil is the presence of a ``burst'' of linear momentum flux emitted slightly
before coalescence. When using the most natural expression for the linear
momentum flux during the plunge, together with a Taylor-expanded
correction factor, we find that the maximum value of the terminal recoil is
km/s and occurs for a mass ratio . We comment,
however, on the fact that the above `best bet estimate' is subject to strong
uncertainties because the location and amplitude of the crucial peak of linear
momentum flux happens at a moment during the plunge where most of the
simplifying analytical assumptions underlying the Effective One Body approach
are no longer justified. Changing the analytical way of estimating the linear
momentum flux, we find maximum recoils that range between 49 and 172 km/s.
(Abridged)Comment: 46 pages, new figures and discussions, to appear in PR
Recoiling Black Holes in Quasars
Recent simulations of merging black holes with spin give recoil velocities
from gravitational radiation up to several thousand km/s. A recoiling
supermassive black hole can retain the inner part of its accretion disk,
providing fuel for a continuing QSO phase lasting millions of years as the hole
moves away from the galactic nucleus. One possible observational manifestation
of a recoiling accretion disk is in QSO emission lines shifted in velocity from
the host galaxy. We have examined QSOs from the Sloan Digital Sky Survey with
broad emission lines substantially shifted relative to the narrow lines. We
find no convincing evidence for recoiling black holes carrying accretion disks.
We place an upper limit on the incidence of recoiling black holes in QSOs of 4%
for kicks greater than 500 km/s and 0.35% for kicks greater than 1000 km/s
line-of-sight velocity.Comment: 4 pages, 4 figures, uses emulateapj, Submitted to ApJ Letter
Gamma-ray emission from dark matter wakes of recoiled black holes
A new scenario for the emission of high-energy gamma-rays from dark matter
annihilation around massive black holes is presented. A black hole can leave
its parent halo, by means of gravitational radiation recoil, in a merger event
or in the asymmetric collapse of its progenitor star. A recoiled black hole
which moves on an almost-radial orbit outside the virial radius of its central
halo, in the cold dark matter background, reaches its apapsis in a finite time.
Near or at the apapsis passage, a high-density wake extending over a large
radius of influence, forms around the black hole. It is shown that significant
gamma-ray emission can result from the enhancement of neutralino annihilation
in these wakes. At its apapsis passage, a black hole is shown to produce a
flash of high-energy gamma-rays whose duration is determined by the mass of the
black hole and the redshift at which it is ejected. The ensemble of such black
holes in the Hubble volume is shown to produce a diffuse high-energy gamma-ray
background whose magnitude is compared to the diffuse emission from dark matter
haloes alone.Comment: version to appear in Astrophysical Journal letters (labels on Fig. 3
corrected
Recoil velocities from equal-mass binary black-hole mergers: a systematic investigation of spin-orbit aligned configurations
Binary black-hole systems with spins aligned with the orbital angular
momentum are of special interest, as studies indicate that this configuration
is preferred in nature. If the spins of the two bodies differ, there can be a
prominent beaming of the gravitational radiation during the late plunge,
causing a recoil of the final merged black hole. We perform an accurate and
systematic study of recoil velocities from a sequence of equal-mass black holes
whose spins are aligned with the orbital angular momentum, and whose individual
spins range from a = +0.584 to -0.584. In this way we extend and refine the
results of a previous study and arrive at a consistent maximum recoil of 448 +-
5 km/s for anti-aligned models as well as to a phenomenological expression for
the recoil velocity as a function of spin ratio. This relation highlights a
nonlinear behavior, not predicted by the PN estimates, and can be readily
employed in astrophysical studies on the evolution of binary black holes in
massive galaxies. An essential result of our analysis is the identification of
different stages in the waveform, including a transient due to lack of an
initial linear momentum in the initial data. Furthermore we are able to
identify a pair of terms which are largely responsible for the kick, indicating
that an accurate computation can be obtained from modes up to l=3. Finally, we
provide accurate measures of the radiated energy and angular momentum, finding
these to increase linearly with the spin ratio, and derive simple expressions
for the final spin and the radiated angular momentum which can be easily
implemented in N-body simulations of compact stellar systems. Our code is
calibrated with strict convergence tests and we verify the correctness of our
measurements by using multiple independent methods whenever possible.Comment: 24 pages, 15 figures, 5 table
Exploring black hole superkicks
Recent calculations of the recoil velocity in black-hole binary mergers have
found kick velocities of km/s for equal-mass binaries with
anti-aligned initial spins in the orbital plane. In general the dynamics of
spinning black holes can be extremely complicated and are difficult to analyze
and understand. In contrast, the ``superkick'' configuration is an example with
a high degree of symmetry that also exhibits exciting physics. We exploit the
simplicity of this ``test case'' to study more closely the role of spin in
black-hole recoil and find that: the recoil is with good accuracy proportional
to the difference between the modes of , the major
contribution to the recoil occurs within before and after the merger, and
that this is after the time at which a standard post-Newtonian treatment breaks
down. We also discuss consequences of the asymmetry in the
gravitational wave signal for the angular dependence of the SNR and the
mismatch of the gravitational wave signals corresponding to the north and south
poles
The gravitational wave rocket
Einstein's equations admit solutions corresponding to photon rockets. In
these a massive particle recoils because of the anisotropic emission of
photons. In this paper we ask whether rocket motion can be powered only by the
emission of gravitational waves. We use the double series approximation method
and show that this is possible. A loss of mass and gain in momentum arise in
the second approximation because of the emission of quadrupole and octupole
waves.Comment: 10 pages LaTe
Consequences of gravitational radiation recoil
Coalescing binary black holes experience an impulsive kick due to anisotropic
emission of gravitational waves. We discuss the dynamical consequences of the
recoil accompanying massive black hole mergers. Recoil velocities are
sufficient to eject most coalescing black holes from dwarf galaxies and
globular clusters, which may explain the apparent absence of massive black
holes in these systems. Ejection from giant elliptical galaxies would be rare,
but coalescing black holes are displaced from the center and fall back on a
time scale of order the half-mass crossing time. Displacement of the black
holes transfers energy to the stars in the nucleus and can convert a steep
density cusp into a core. Radiation recoil calls into question models that grow
supermassive black holes from hierarchical mergers of stellar-mass precursors.Comment: 5 pages, 4 figures, emulateapj style; minor changes made; accepted to
ApJ Letter
Constraints from Gravitational Recoil on the Growth of Supermassive Black Holes at High Redshift
Recent studies have shown that during their coalescence, binary supermassive
black holes (SMBHs) experience a gravitational recoil with velocities of 100
km/s < v(kick) < 600 km/s. These velocities exceed the escape velocity v(esc)
from typical dark matter (DM) halos at high-redshift (z>6), and therefore put
constraints on scenarios in which early SMBHs grow at the centers of DM halos.
Here we quantify these constraints for the most distant known SMBHs, with
inferred masses in excess of 10^9 M(sun), powering the bright quasars
discovered in the Sloan Digital Sky Survey at z>6. We assume that these SMBHs
grew via a combination of accretion and mergers between pre-existing seed BHs
in individual progenitor halos, and that mergers between progenitors with
v(esc) < v(kick) disrupt the BH growth process. Our results suggest that under
these assumptions, the z=6 SMBHs had a phase during which gained mass
significantly more rapidly than under an Eddington-limited exponential growth
rate.Comment: submitted to ApJ Letters, 5 emulateapj pages with 1 figur
- …