317 research outputs found
Robust Evidence for the Breakdown of Standard Gravity at Low Acceleration from Statistically Pure Binaries Free of Hidden Companions
It is found that Gaia DR3 binary stars selected with stringent requirements
on astrometric measurements and radial velocities naturally satisfy Newtonian
dynamics without hidden close companions when projected separation kau,
showing that pure binaries can be selected. It is then found that pure binaries
selected with the same criteria show a systematic deviation from the Newtonian
expectation when kau. When both proper motions and parallaxes are
required to have precision better than 0.003 and radial velocities better than
0.2, I obtain 1558 statistically pure binaries within a 'clean' -band
absolute magnitude range. From this sample, I obtain an observed to Newtonian
predicted kinematic acceleration ratio of
for acceleration m s, in excellent agreement with a recent finding for a much larger general sample with the amount of hidden close
companions self-calibrated. I also investigate the radial profile of stacked
sky-projected relative velocities without a deprojection to the 3D space. The
observed profile matches the Newtonian predicted profile for kau
without any free parameters but shows a clear deviation at a larger separation
with a significance of . The projected velocity boost factor for
kau is measured to be matching
. Finally, for a small sample of 23 binaries with
exceptionally precise radial velocities (precision ) the directly
measured relative velocities in the 3D space also show a boost at larger
separations. These results robustly confirm the recently reported gravitational
anomaly at low acceleration for a general sample.Comment: 14 pages, 12 figures, submitted to ApJ. This new work complements the
recent paper Chae (2023, ApJ, 952, 128 [arXiv:2305.04613]) in an important
wa
Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars
A gravitational anomaly is found at weak gravitational acceleration
m s from analyses of the dynamics of wide binary
stars selected from the Gaia DR3 database that have accurate distances, proper
motions, and reliably inferred stellar masses. Implicit high-order
multiplicities are required and the multiplicity fraction is calibrated so that
binary internal motions agree statistically with Newtonian dynamics at a high
enough acceleration of m s. The observed sky-projected motions
and separation are deprojected to the three-dimensional relative velocity
and separation through a Monte Carlo method, and a statistical relation
between the Newtonian acceleration (where is the
total mass of the binary system) and a kinematic acceleration
is compared with the corresponding relation predicted by Newtonian dynamics.
The empirical acceleration relation at m s systematically
deviates from the Newtonian expectation. A gravitational anomaly parameter
between the observed acceleration at and
the Newtonian prediction is measured to be: and at and
m s, from the main sample of 26,615 wide binaries within 200 pc. These
two deviations in the same direction represent a significance. The
deviation represents a direct evidence for the breakdown of standard gravity at
weak acceleration. At m s, the observed to
Newton predicted acceleration ratio is
.
This systematic deviation agrees with the boost factor that the AQUAL theory
predicts for kinematic accelerations in circular orbits under the Galactic
external field.Comment: 37 pages, 36 figures, accepted for publication in the Astrophysical
Journa
Limits on the evolution of galaxies from the statistics of gravitational lenses
We use gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS) to
constrain the evolution of galaxies since redshift in the current
\LCDM cosmology. This constraint is unique as it is based on a mass-selected
lens sample of galaxies. Our method of statistical analysis is the same as in
Chae (2003). We parametrise the early-type number density evolution in the form
of and the velocity dispersion as . We find that
() if we assume , implying
that the number density of early-type galaxies is within 50% to 164% of the
present-day value at redshift . Allowing the velocity dispersion to
evolve, we find that (), indicating that
the velocity dispersion must be within 57% and 107% of the present-day value at
. These results are consistent with the early formation and passive
evolution of early-type galaxies. More stringent limits from lensing can be
obtained from future large lens surveys and by using very high-redshift quasars
(z \ga 5) such as those found from the Sloan Digital Sky Survey.Comment: 10 pages (preprint format), 2 figures, ApJL in press (December 20th
issue
Cosmological Parameters from the SDSS DR5 Velocity Dispersion Function of Early-Type Galaxies through Radio-Selected Lens Statistics
We improve strong lensing constraints on cosmological parameters in light of
the new measurement of the velocity dispersion function of early-type galaxies
based on the SDSS DR5 data and recent semi-analytical modeling of galaxy
formation. Using both the number statistics of the CLASS statistical sample and
the image separation distribution of the CLASS and the PANELS radio-selected
lenses, we find the cosmological matter density \Om = 0.25^{+0.12}_{-0.08}
(68% CL) assuming evolutions of galaxies predicted by a semi-analytical model
of galaxy formation and \Om = 0.26^{+0.12}_{-0.08} assuming no evolution of
galaxies for a flat cosmology with an Einstein cosmological constant. For a
flat cosmology with a generalized dark energy, we find the non-evolving dark
energy equation of state () at the 68% CL (95% CL).Comment: ApJL, accepted (results and presentations revised; conclusions
unchanged
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