52 research outputs found
Constraints on the Size of Extra Dimensions from the Orbital Evolution of the Black-Hole X-Ray Binary XTE J1118+480
In a universe of the Randall-Sundrum type, black holes are unstable and emit
gravitational modes in the extra dimension. This leads to dramatically
shortened lifetimes of astrophysical black holes and to an observable change of
the orbital period of black-hole binaries. I obtain an upper limit on the rate
of change of the orbital period of the binary XTE J1118+480 and constrain the
asymptotic curvature radius of the extra dimension to a value that is of the
same order as the constraints from other astrophysical sources. A unique
property of XTE J1118+480 is that the expected rate of change of the orbital
period due to magnetic braking alone is so large that only one additional
measurement of the orbital period would lead to the first detection of orbital
evolution of a black-hole binary and impose the tightest constraint to date on
the size of one extra dimension of the order of 35 microns.Comment: accepted for publication in A&
Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum: II. Black-Hole Images
According to the no-hair theorem, all astrophysical black holes are fully
described by their masses and spins. This theorem can be tested observationally
by measuring (at least) three different multipole moments of the spacetimes of
black holes. In this paper, we analyze images of black holes within a framework
that allows us to calculate observables in the electromagnetic spectrum as a
function of the mass, spin, and, independently, the quadrupole moment of a
black hole. We show that a deviation of the quadrupole moment from the expected
Kerr value leads to images of black holes that are either prolate or oblate
depending on the sign and magnitude of the deviation. In addition, there is a
ring-like structure around the black-hole shadow with a diameter of about 10
black-hole masses that is substantially brighter than the image of the
underlying accretion flow and that is independent of the astrophysical details
of accretion flow models. We show that the shape of this ring depends directly
on the mass, spin, and quadrupole moment of the black hole and can be used for
an independent measurement of all three parameters. In particular, we
demonstrate that this ring is highly circular for a Kerr black hole with a spin
a<0.9M, independent of the observer's inclination, but becomes elliptical and
asymmetric if the no-hair theorem is violated. Near-future very-long baseline
interferometric observations of Sgr A* will image this ring and may allow for
an observational test of the no-hair theorem.Comment: Accepted for publication in Ap
Tests of General Relativity in the Strong Gravity Regime Based on X-Ray Spectropolarimetric Observations of Black Holes in X-Ray Binaries
Although General Relativity (GR) has been tested extensively in the weak
gravity regime, similar tests in the strong gravity regime are still missing.
In this paper we explore the possibility to use X-ray spectropolarimetric
observations of black holes in X-ray binaries to distinguish between the Kerr
metric and the phenomenological metrics introduced by Johannsen and Psaltis
(2011) (which are not vacuum solutions of Einstein's equation) and thus to test
the no-hair theorem of GR. To this end, we have developed a numerical code that
calculates the radial brightness profiles of accretion disks and parallel
transports the wave vector and polarization vector of photons through the Kerr
and non-GR spacetimes. We used the code to predict the observational appearance
of GR and non-GR accreting black hole systems. We find that the predicted
energy spectra and energy dependent polarization degree and polarization
direction do depend strongly on the underlying spacetime. However, for large
regions of the parameter space, the GR and non-GR metrics lead to very similar
observational signatures, making it difficult to observationally distinguish
between the two types of models.Comment: 27 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum: I. Properties of a Quasi-Kerr Spacetime
According to the no-hair theorem, an astrophysical black hole is uniquely
described by only two quantities, the mass and the spin. In this series of
papers, we investigate a framework for testing the no-hair theorem with
observations of black holes in the electromagnetic spectrum. We formulate our
approach in terms of a parametric spacetime which contains a quadrupole moment
that is independent of both mass and spin. If the no-hair theorem is correct,
then any deviation of the black-hole quadrupole moment from its Kerr value has
to be zero. We analyze in detail the properties of this quasi-Kerr spacetime
that are critical to interpreting observations of black holes and demonstrate
their dependence on the spin and quadrupole moment. In particular, we show that
the location of the innermost stable circular orbit and the gravitational
lensing experienced by photons are affected significantly at even modest
deviations of the quadrupole moment from the value predicted by the no-hair
theorem. We argue that observations of black-hole images, of relativistically
broadened iron lines, as well as of thermal X-ray spectra from accreting black
holes will lead in the near future to an experimental test of the no-hair
theorem.Comment: Accepted for publication in Ap
Theory of Alike Selectivity in Biological Channels
We introduce a statistical mechanical model of the selectivity filter that accounts for the interaction between ions within the channel and derive Eisenman equation of the filter selectivity directly from the condition of barrier-less conduction
Black hole solutions in massive gravity
The static vacuum spherically symmetric solutions in massive gravity are
obtained both analytically and numerically. The solutions depend on two
parameters (integration constants): the mass M (or, equivalently, the
Schwarzschild radius), and an additional parameter, the "scalar charge" S. At
zero value of S and positive mass the standard Schwarzschild black hole
solutions are recovered. Depending on the parameters of the model and the signs
of M and S, the solutions may or may not have horizon. Those with the horizon
describe modified black holes provided they are stable against small
perturbations. In the analytically solvable example, the modified black hole
solutions may have both attractive and repulsive (anti-gravitating) behavior at
large distances. At intermediate distances the gravitational potential of a
modified black hole may mimics the presence of dark matter. Modified black hole
solutions are also found numerically in more realistic massive gravity models
which are attractors of the cosmological evolution.Comment: Original version + erratu
Measuring the spin of the primary black hole in OJ287
The compact binary system in OJ287 is modelled to contain a spinning primary
black hole with an accretion disk and a non-spinning secondary black hole.
Using Post Newtonian (PN) accurate equations that include 2.5PN accurate
non-spinning contributions, the leading order general relativistic and
classical spin-orbit terms, the orbit of the binary black hole in OJ287 is
calculated and as expected it depends on the spin of the primary black hole.
Using the orbital solution, the specific times when the orbit of the secondary
crosses the accretion disk of the primary are evaluated such that the record of
observed outbursts from 1913 up to 2007 is reproduced. The timings of the
outbursts are quite sensitive to the spin value. In order to reproduce all the
known outbursts, including a newly discovered one in 1957, the Kerr parameter
of the primary has to be . The quadrupole-moment contributions
to the equations of motion allow us to constrain the `no-hair' parameter to be
where 0.3 is the one sigma error. This supports the `black hole
no-hair theorem' within the achievable precision.
It should be possible to test the present estimate in 2015 when the next
outburst is due. The timing of the 2015 outburst is a strong function of the
spin: if the spin is 0.36 of the maximal value allowed in general relativity,
the outburst begins in early November 2015, while the same event starts in the
end of January 2016 if the spin is 0.2Comment: 12 pages, 6 figure
Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic Spectrum
According to the no-hair theorem, astrophysical black holes are uniquely
described by their mass and spin. In this paper, we review a new framework for
testing the no-hair hypothesis with observations in the electromagnetic
spectrum. The approach is formulated in terms of a Kerr-like spacetime
containing a quadrupole moment that is independent of both mass and spin. If
the no-hair theorem is correct, then any deviation from the Kerr metric
quadrupole has to be zero. We show how upcoming VLBI imaging observations of
Sgr A* as well as spectroscopic observations of iron lines from accreting black
holes with IXO may lead to the first astrophysical test of the no-hair theorem.Comment: 5 pages, 3 figures, to appear in Adv. Space Res., Proc. COSPAR 201
Formation of the black-hole binary M33 X-7 via mass-exchange in a tight massive system
M33 X-7 is among the most massive X-Ray binary stellar systems known, hosting
a rapidly spinning 15.65 Msun black hole orbiting an underluminous 70 Msun Main
Sequence companion in a slightly eccentric 3.45 day orbit. Although
post-main-sequence mass transfer explains the masses and tight orbit, it leaves
unexplained the observed X-Ray luminosity, star's underluminosity, black hole's
spin, and eccentricity. A common envelope phase, or rotational mixing, could
explain the orbit, but the former would lead to a merger and the latter to an
overluminous companion. A merger would also ensue if mass transfer to the black
hole were invoked for its spin-up. Here we report that, if M33 X-7 started as a
primary of 85-99 Msun and a secondary of 28-32 Msun, in a 2.8-3.1 day orbit,
its observed properties can be consistently explained. In this model, the Main
Sequence primary transferred part of its envelope to the secondary and lost the
rest in a wind; it ended its life as a ~16 Msun He star with a Fe-Ni core which
collapsed to a black hole (with or without an accompanying supernova). The
release of binding energy and, possibly, collapse asymmetries "kicked" the
nascent black hole into an eccentric orbit. Wind accretion explains the X-Ray
luminosity, while the black hole spin can be natal.Comment: Manuscript: 18 pages, 2 tables, 2 figure. Supplementary Information:
34 pages, 6 figures. Advance Online Publication (AOP) on
http://www.nature.com/nature on October 20, 2010. To Appear in Nature on
November 4, 201
Measuring Black Hole Spin in OJ287
We model the binary black hole system OJ287 as a spinning primary and a
non-spinning secondary. It is assumed that the primary has an accretion disk
which is impacted by the secondary at specific times. These times are
identified as major outbursts in the light curve of OJ287. This identification
allows an exact solution of the orbit, with very tight error limits. Nine
outbursts from both the historical photographic records as well as from recent
photometric measurements have been used as fixed points of the solution: 1913,
1947, 1957, 1973, 1983, 1984, 1995, 2005 and 2007 outbursts. This allows the
determination of eight parameters of the orbit. Most interesting of these are
the primary mass of , the secondary mass , major axis precession rate per period, and the
eccentricity of the orbit 0.70. The dimensionless spin parameter is
(1 sigma). The last parameter will be more tightly
constrained in 2015 when the next outburst is due. The outburst should begin on
15 December 2015 if the spin value is in the middle of this range, on 3 January
2016 if the spin is 0.25, and on 26 November 2015 if the spin is 0.31. We have
also tested the possibility that the quadrupole term in the Post Newtonian
equations of motion does not exactly follow Einstein's theory: a parameter
is introduced as one of the 8 parameters. Its value is within 30% (1 sigma) of
the Einstein's value . This supports the of black
holes within the achievable precision. We have also measured the loss of
orbital energy due to gravitational waves. The loss rate is found to agree with
Einstein's value with the accuracy of 2% (1 sigma).Comment: 12 pages, 4 figures, IAU26
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