40 research outputs found
Life under a black sun
Life is dependent on the income of energy with low entropy and the disposal
of energy with high entropy. On Earth, the low-entropy energy is provided by
solar radiation and the high-entropy energy is disposed as infrared radiation
emitted into the cold space. Here we turn the situation around and assume
cosmic background radiation as the low-entropy source of energy for a planet
orbiting a black hole into which the high-entropy energy is disposed. We
estimate the power that can be produced by thermodynamic processes on such a
planet, with a particular interest in planets orbiting a fast rotating Kerr
black hole as in the science fiction movie {\em Interstellar}. We also briefly
discuss a reverse Dyson sphere absorbing cosmic background radiation from the
outside and dumping waste energy to a black hole inside.Comment: 8 pages, 6 figures. Replaced with the version published in Am. J.
Phy
On a multi-resonant origin of high frequency quasiperiodic oscillations in the neutron-star X-ray binary 4U 1636-53
The results we presented were biased because of the typing error in the code
transcription of the equation (A.12). We will replace by the corrected version
soon. The brief of the corrected results can be found at
http://www.physics.cz/research/doc/posters/1181038112_0.pdfComment: 7 pages, 3 figures, submitted to A&
Stable attractors in the three-dimensional general relativistic Poynting-Robertson effect
We prove the stability of the critical hypersurfaces associated with the
three-dimensional general relativistic Poynting-Robertson effect. The
equatorial ring configures to be as a stable attractor and the whole critical
hypersurface as a basin of attraction for this dynamical system. We introduce a
new, simpler (in terms of calculations), and more physical approach within the
Lyapunov theory. We propose three different Lyapunov functions, each one
carrying important information and very useful for understanding such
phenomenon under different aspects.Comment: 11 pages, 3 figure
Non-geodesic orbital and epicyclic frequencies in vicinity of slowly rotating magnetized neutron stars
We study non-geodesic corrections to the quasicircular motion of charged test
particles in the field of magnetized slowly rotating neutron stars. The
gravitational field is approximated by the Lense-Thirring geometry, the
magnetic field is of the standard dipole character. Using a fully-relativistic
approach we determine influence of the electromagnetic interaction (both
attractive and repulsive) on the quasicircular motion. We focus on the
behaviour of the orbital and epicyclic frequencies of the motion. Components of
the four-velocity of the orbiting charged test particles are obtained by
numerical solution of equations of motion, the epicyclic frequencies are
obtained by using the standard perturbative method. The role of the combined
effect of the neutron star magnetic field and its rotation in the character of
the orbital and epicyclic frequencies is discussed.Comment: 2 pages, to be published in Proceedings of IAUS 290 "Feeding Compact
Objects: Accretion on All Scales", C. M. Zhang, T. Belloni, M. Mendez and S.
N. Zhang (eds.
Genetic selection of neutron star structure matching the X-ray observations
Assuming a resonant origin of the quasiperiodic oscillations observed in the
X-ray neutron star binary systems, we apply a genetic algorithm method for
selection of neutron star models. It was suggested that pairs of kilo-Hertz
peaks in the X-ray Fourier power density spectra of some neutron stars reflect
a non-linear resonance between two modes of accretion disk oscillations. In
several specific models, the two modes are related to physically plausible
combinations of Keplerian, vertical and radial frequencies of geodesic orbital
motion. We investigate this concept for a specific neutron star source, a fixed
pair of modes and various neutron star equations of state. Each neutron star
model is characterized by the equation of state (EOS), rotation frequency
() and central energy density (). These determine the
spacetime structure governing geodesic motion and position dependent radial and
vertical epicyclic oscillations related to the stable circular geodesics. When
the parameters of neutron star model are fixed, the two considered modes imply
a frequency-frequency relation which can be compared to the observation in
order to eliminate the unsatisfactory sets (KR,, EOS).
For the elimination we use the advanced genetic algorithm. Genetic algorithm
comes out from the method of natural selection when subjects with the best
adaptation to assigned conditions have best chances to survive. The chosen
genetic algorithm with sexual reproduction contains one chromosome with
restricted lifetime, uniform crossing and genes of type 3/3/5. For encryption
of physical description (KR,, EOS) into chromosome we
use the Gray code. As a fitness function we use correspondence between the
observed and calculated pairs of eigenfrequencies.Comment: 9 pages, 1 figur
Habitable zones around almost extremely spinning black holes (black sun revisited)
We analyzed the thermodynamics of hypothetical exoplanets at very low
Keplerian circular orbits in close vicinity of rapidly spinning supermassive
black holes. Such black hole exoplanets are heated by strongly blueshifted and
focused flux of the incoming cosmic microwave background (CMB) and cooled by
the cold part of the local sky containing the black hole shadow. This gives
rise to a temperature difference, which can drive processes far from
thermodynamic equilibrium in a hypothetical life form inhabiting black hole
exoplanets, similar to the case of a planet heated by the radiation of the
parent star and cooled by the night sky. We found that for a narrow range of
radii of very low Keplerian circular orbits and for very high spin of a
supermassive black hole, the temperature regime of the black hole exoplanets
corresponds to the habitable zone around standard stars. The thermodynamics of
black hole exoplanets therefore, in principle, does not exclude the existence
of life based on known biology. The peak of the multiblackbody spectral profile
of the CMB heating the exoplanet is located in the ultraviolet band, but a
significant fraction of the flux comes also in the visible and infrared bands.
The minimum mass of a black hole ensuring the resistance to tidal disruption of
an Earth-like exoplanet orbiting in the habitable zone is estimated to .Comment: 13 pages, 7 figure
Restrictions to neutron star properties based on twin-peak quasi-periodic oscillations
We consider twin-peak quasi-periodic oscillations observed in the accreting
low-mass neutron star binaries and explore restrictions to central compact
object properties that are implied by various QPO models. For each model and
each source, the consideration results in a specific relation between the
compact object mass and the angular-momentum rather than in their
single preferred combination. Moreover, restrictions on the models resulting
from observations of the low-frequency sources are weaker than those in the
case of the high-frequency sources.Comment: 2 pages, to be published in Proceedings of IAUS 290 "Feeding Compact
Objects: Accretion on All Scales", C. M. Zhang, T. Belloni, M. Mendez and S.
N. Zhang (eds.
Mass-angular-momentum relations implied by models of twin peak quasi-periodic oscillations
Twin peak quasi-periodic oscillations (QPOs) appear in the X-ray
power-density spectra of several accreting low-mass neutron star (NS) binaries.
Observations of the peculiar Z-source Circinus X-1 display unusually low QPO
frequencies. Using these observations, we have previously considered the
relativistic precession (RP) twin peak QPO model to estimate the mass of
central NS in Circinus X-1. We have shown that such an estimate results in a
specific mass-angular-momentum (M-j) relation rather than a single preferred
combination of M and j. Here we confront our previous results with another
binary, the atoll source 4U 1636-53 that displays the twin peak QPOs at very
high frequencies, and extend the consideration to various twin peak QPO models.
In analogy to the RP model, we find that these imply their own specific M-j
relations. We explore these relations for both sources and note differences in
the chi-square behavior that represent a dichotomy between high- and
low-frequency sources. Based on the RP model, we demonstrate that this
dichotomy is related to a strong variability of the model predictive power
across the frequency plane. This variability naturally comes from the radial
dependence of characteristic frequencies of orbital motion. As a consequence,
the restrictions on the models resulting from observations of low-frequency
sources are weaker than those in the case of high-frequency sources. Finally we
also discuss the need for a correction to the RP model and consider the
removing of M-j degeneracies, based on the twin peak QPO-independent angular
momentum estimates.Comment: 16 pages, 7 figure
On one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations
Twin-peak quasi-periodic oscillations (QPOs) are observed in several low-mass
X-ray binary systems containing neutron stars (NSs). Timing analysis of X-ray
fluxes of more than dozen of such systems reveals remarkable correlations
between the frequencies of two characteristic peaks present in the power
density spectra. The individual correlations clearly differ, but they roughly
follow a common individual pattern. High values of measured QPO frequencies and
strong modulation of the X-ray flux both suggest that the observed correlations
are connected to orbital motion in the innermost part of an accretion disc.
Several attempts to model these correlations with simple geodesic orbital
models or phenomenological relations have failed in the past. We find and
explore a surprisingly simple analytic relation that reproduces individual
correlations for a group of several sources through a single parameter. When an
additional free parameter is considered within our relation, it well reproduces
the data of a large group of 14 sources. The very existence and form of this
simple relation supports the hypothesis of the orbital origin of QPOs and
provides the key for further development of QPO models. We discuss a possible
physical interpretation of our relation's parameters and their links to
concrete QPO models.Comment: 6 pages, 2 figures, 1 table, accepted for publication in Monthly
Notices of the Royal Astronomical Society: Letter
Three-dimensional general relativistic Poynting-Robertson effect. III. Static and non-spherical quadrupolar massive source
We investigate the three-dimensional motion of a test particle in the
gravitational field generated by a non-spherical compact object endowed with a
mass quadrupole moment, described by the Erez-Rosen metric, and a radiation
field, including the general relativistic Poynting-Robertson effect, coming
from a rigidly rotating spherical emitting source located outside of the
compact object. We derive the equations of motion for test particles influenced
by such radiation field, recovering the two-dimensional description, and the
weak-field approximation. This dynamical system admits the existence of a
critical hypersurface, region where gravitational and radiation forces balance.
Selected test particle orbits for different set of input parameters are
displayed. The possible configurations on the critical hypersurfaces can be
either latitudinal drift towards the equatorial ring or suspended orbits. We
discuss about the existence of multiple hypersurface solutions through a simple
method to perform the calculations. We graphically prove also that the critical
hypersurfaces are stable configurations within the Lyapunov theory.Comment: 16 pages, 11 figures. Paper accepted on the 2nd of June 2020 on Phys.
Rev.