5,715 research outputs found
On hydrogen bond correlations at high pressures
In situ high pressure neutron diffraction measured lengths of O H and H O
pairs in hydrogen bonds in substances are shown to follow the correlation
between them established from 0.1 MPa data on different chemical compounds. In
particular, the conclusion by Nelmes et al that their high pressure data on ice
VIII differ from it is not supported. For compounds in which the O H stretching
frequencies red shift under pressure, it is shown that wherever structural data
is available, they follow the stretching frequency versus H O (or O O) distance
correlation. For compounds displaying blue shifts with pressure an analogy
appears to exist with improper hydrogen bonds.Comment: 12 pages,4 figure
Testing the Kerr metric with X-ray Reflection Spectroscopy of Mrk 335 Suzaku data
Einstein's gravity has undergone extensive tests in the weak field
gravitational limit, with results in agreement with theoretical predictions.
There exist theories beyond general relativity (GR) which modify gravity in the
strong field regime but agree with GR in the weak field. Astrophysical black
holes are believed to be described by the Kerr metric and serve as suitable
candidates to test strong gravity with electromagnetic radiation. We perform
such a test by fitting one Suzaku dataset of the narrow-line Seyfert 1 (NLS1)
galaxy Mrk 335 with X-ray reflection spectroscopy, using the Johannsen metric
to model the black hole spacetime and test for deviations from Kerr. We find
the data is best modeled with a hybrid model that includes both partial
covering absorption and a reflection component. This is the first time such a
model has been proposed for a high-flux (low reflection) Mrk 335 dataset. We
constrain the Johannsen deformation parameter to
, and the
parameter to , both at the 99%
confidence level. Although additional solutions at large deviations from the
Kerr metric show statistical similarity with the ones above, further analysis
suggests these solutions may be manifestations of uncertainties beyond our
control and do not represent the data. Hence, our results are in agreement with
the idea that the supermassive compact object at the center of Mrk 335 is
described by the Kerr metric.Comment: 13 pages, 9 figures. v2: refereed versio
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&
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&
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