377 research outputs found
Black Hole Spectrum: Continuous or Discrete?
We formulate a qualitative argument, based on Heisenberg's uncertainty
principle, to support the claim that when the effects of matter fields are
assumed to overshadow the effects of quantum mechanics of spacetime, the
discrete spectrum of black hole radiation, as such as predicted by Bekenstein's
proposal for a discrete black hole area spectrum, reduces to Hawking's
black-body spectrum.Comment: 7 pages, no figure
Discrete Black-Hole Radiation and the Information Loss Paradox
Hawking's black hole information puzzle highlights the incompatibility
between our present understanding of gravity and quantum physics. However,
Hawking's prediction of black-hole evaporation is at a semiclassical level. One
therefore suspects some modifications of the character of the radiation when
quantum properties of the {\it black hole itself} are properly taken into
account. In fact, during the last three decades evidence has been mounting
that, in a quantum theory of gravity black holes may have a discrete mass
spectrum, with concomitant {\it discrete} line emission. A direct consequence
of this intriguing prediction is that, compared with blackbody radiation,
black-hole radiance is {\it less} entropic, and may therefore carry a
significant amount of {\it information}. Using standard ideas from quantum
information theory, we calculate the rate at which information can be recovered
from the black-hole spectral lines. We conclude that the information that was
suspected to be lost may gradually leak back, encoded into the black-hole
spectral lines.Comment: 12 page
Black-hole radiation, the fundamental area unit, and the spectrum of particle species
Bekenstein and Mukhanov have put forward the idea that, in a quantum theory
of gravity a black hole should have a discrete mass spectrum with a concomitant
{\it discrete} line emission. We note that a direct consequence of this
intriguing prediction is that, compared with blackbody radiation, black-hole
radiance is {\it less} entropic. We calculate the ratio of entropy emission
rate from a quantum black hole to the rate of black-hole entropy decrease, a
quantity which, according to the generalized second law (GSL) of
thermodynamics, should be larger than unity. Implications of our results for
the GSL, for the value of the fundamental area unit in quantum gravity, and for
the spectrum of massless particles in nature are discussed.Comment: 4 page
Implications of primordial black holes on the first stars and the origin of the super--massive black holes
If the cosmological dark matter has a component made of small primordial
black holes, they may have a significant impact on the physics of the first
stars and on the subsequent formation of massive black holes. Primordial black
holes would be adiabatically contracted into these stars and then would sink to
the stellar center by dynamical friction, creating a larger black hole which
may quickly swallow the whole star. If these primordial black holes are heavier
than , the first stars would likely live only for a very
short time and would not contribute much to the reionization of the universe.
They would instead become black holes which (depending on
subsequent accretion) could serve as seeds for the super--massive black holes
seen at high redshifts as well as those inside galaxies today.Comment: 16 pages, 2 figures. v2: refereed versio
Implications of Space-Time foam for Entanglement Correlations of Neutral Kaons
The role of invariance and consequences for bipartite entanglement of
neutral (K) mesons are discussed. A relaxation of leads to a modification
of the entanglement which is known as the effect. The relaxation of
assumptions required to prove the theorem are examined within the context
of models of space-time foam. It is shown that the evasion of the EPR type
entanglement implied by (which is connected with spin statistics) is
rather elusive. Relaxation of locality (through non-commutative geometry) or
the introduction of decoherence by themselves do not lead to a destruction of
the entanglement. So far we find only one model which is based on non-critical
strings and D-particle capture and recoil that leads to a stochastic
contribution to the space-time metric and consequent change in the neutral
meson bipartite entanglement. The lack of an omega effect is demonstrated for a
class of models based on thermal like baths which are generally considered as
generic models of decoherence
The Magnetic Fields of Millisecond Pulsars in Globular Clusters
Many of the characteristic properties of the millisecond pulsars found in
globular clusters are markedly different from those in the Galactic disc. We
find that one such physical parameter is the surface magnetic field strength.
Even though the average spin-periods do not differ much the average surface
magnetic field is 2-5 times larger in the globular cluster pulsars. This effect
could be apparent, arising due to one or more of several biases. Alternatively,
if future observations confirm this effect to be real, then this could be
interpreted as a preferential recycling of pulsars in tight binaries where the
mass transfer takes place at high accretion rates.Comment: 11 pages, 6 figures : final published versio
General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes
Black hole (BH) accretion flows and jets are qualitatively affected by the
presence of ordered magnetic fields. We study fully three-dimensional global
general relativistic magnetohydrodynamic (MHD) simulations of radially extended
and thick (height to cylindrical radius ratio of )
accretion flows around BHs with various dimensionless spins (, with BH
mass ) and with initially toroidally-dominated (-directed) and
poloidally-dominated ( directed) magnetic fields. Firstly, for toroidal
field models and BHs with high enough , coherent large-scale (i.e. ) dipolar poloidal magnetic flux patches emerge, thread the BH, and generate
transient relativistic jets. Secondly, for poloidal field models, poloidal
magnetic flux readily accretes through the disk from large radii and builds-up
to a natural saturation point near the BH. For sufficiently high or low
the polar magnetic field compresses the inflow into a geometrically
thin highly non-axisymmetric "magnetically choked accretion flow" (MCAF) within
which the standard linear magneto-rotational instability is suppressed. The
condition of a highly-magnetized state over most of the horizon is optimal for
the Blandford-Znajek mechanism that generates persistent relativistic jets with
% efficiency for . A magnetic Rayleigh-Taylor
and Kelvin-Helmholtz unstable magnetospheric interface forms between the
compressed inflow and bulging jet magnetosphere, which drives a new jet-disk
quasi-periodic oscillation (JD-QPO) mechanism. The high-frequency QPO has
spherical harmonic mode period of for
with coherence quality factors . [abridged]Comment: 32 pages + acks/appendix/references, 22 figures, 10 tables. MNRAS in
press. High-Res Version: http://www.slac.stanford.edu/~jmckinne/mcaf.pdf .
Fiducial Movie: http://youtu.be/V2WoJOkIin
Very high frequency gravitational wave background in the universe
Astrophysical sources of high frequency gravitational radiation are
considered in association with a new interest to very sensitive HFGW receivers
required for the laboratory GW Hertz experiment. A special attention is paid to
the phenomenon of primordial black holes evaporation. They act like black body
to all kinds of radiation, including gravitons, and, therefore, emit an
equilibrium spectrum of gravitons during its evaporation. Limit on the density
of high frequency gravitons in the Universe is obtained, and possibilities of
their detection are briefly discussed.Comment: 14 page
General-relativistic model of hot accretion flows with global Compton cooling
We present a model of optically thin, two-temperature, accretion flows using
an exact Monte Carlo treatment of global Comptonization, with seed photons from
synchrotron and bremsstrahlung emission, as well as with a fully general
relativistic description of both the radiative and hydrodynamic processes. We
consider accretion rates for which the luminosities of the flows are between
~0.001 and 0.01 of the Eddington luminosity. The black hole spin parameter
strongly affects the flow structure within the innermost 10 gravitational
radii. The resulting large difference between the Coulomb heating in models
with a non-rotating and a rapidly rotating black hole is, however, outweighed
by a strong contribution of compression work, much less dependent on spin. The
consequent reduction of effects related to the value of the black spin is more
significant at smaller accretion rates. For a non-rotating black hole, the
compressive heating of electrons dominates over their Coulomb heating, and
results in an approximately constant radiative efficiency of approximately 0.4
per cent in the considered range of luminosities. For a rapidly rotating black
hole, the Coulomb heating dominates, the radiative efficiency is ~1 per cent
and it slightly increases (but less significantly than estimated in some
previous works) with increasing accretion rate. We find an agreement between
our model, in which the synchrotron emission is the main source of seed
photons, and observations of black-hole binaries in their hard states and AGNs
at low luminosities. In particular, our model predicts a hardening of the X-ray
spectrum with increasing luminosity, as indeed observed below ~0.01 of the
Eddington luminosity in both black-hole binaries and AGNs. Also, our model
approximately reproduces the luminosity and the slope of the X-ray emission in
Cen A.Comment: 13 pages, MNRAS, accepte
The spectrum of quantum black holes and quasinormal modes
The spectrum of multiple level transitions of the quantum black hole is
considered, and the line widths calculated. Initial evidence is found for these
higher order transitions in the spectrum of quasinormal modes for Schwarzschild
and Kerr black holes, further bolstering the idea that there exists a
correspondence principle between quantum transitions and classical ``ringing
modes''. Several puzzles are noted, including a fine-tuning problem between the
line width and the level degeneracy. A more general explanation is provided for
why setting the Immirzi parameter of loop quantum gravity from the black hole
spectrum necessarily gives the correct value for the black hole entropy.Comment: 5 pages, 5 figures, version to appear in Phys. Rev.
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