1,212 research outputs found
Constraints on the Neutron Star Equation of State from GW170817
The first detection of gravitational waves from a neutron star-neutron star
merger, GW170817, has opened up a new avenue for constraining the
ultradense-matter equation of state (EOS). The deviation of the observed
waveform from a point-particle waveform is a sensitive probe of the EOS
controlling the merging neutron stars' structure. In this topical review, I
discuss the various constraints that have been made on the EOS in the year
following the discovery of GW170817. In particular, I review the surprising
relationship that has emerged between the effective tidal deformability of the
binary system and the neutron star radius. I also report new results that make
use of this relationship, finding that the radius inferred from GW170817 lies
between 9.8 and 13.2 km at 90% confidence, with distinct likelihood peaks at
10.8 and 12.3 km. I compare these radii, as well as those inferred in the
literature, to X-ray measurements of the neutron star radius. I also summarize
the various maximum mass constraints, which point towards a maximum mass < 2.3
M_sun, depending on the fate of the remnant, and which can be used to
additionally constrain the high-density EOS. I review the constraints on the
EOS that have been performed directly, through Bayesian inference schemes.
Finally, I comment on the importance of disentangling thermal effects in future
EOS constraints from neutron star mergers.Comment: Invited contribution to the EPJA topical issue "The first neutron
star merger observation - Implications for nuclear physics
Tidal deformability from GW170817 as a direct probe of the neutron star radius
Gravitational waves from the coalescence of two neutron stars were recently
detected for the first time by the LIGO-Virgo collaboration, in event GW170817.
This detection placed an upper limit on the effective tidal deformability of
the two neutron stars and tightly constrained the chirp mass of the system. We
report here on a new simplification that arises in the effective tidal
deformability of the binary, when the chirp mass is specified. We find that, in
this case, the effective tidal deformability of the binary is surprisingly
independent of the component masses of the individual neutron stars, and
instead depends primarily on the ratio of the chirp mass to the neutron star
radius. Thus, a measurement of the effective tidal deformability can be used to
directly measure the neutron star radius. We find that the upper limit on the
effective tidal deformability from GW170817 implies that the radius cannot be
larger than ~13km, at the 90% level, independent of the assumed masses for the
component stars. The result can be applied generally, to probe the stellar
radii in any neutron star-neutron star merger with a measured chirp mass. The
approximate mass-independence disappears for neutron star-black hole mergers.
Finally, we discuss a Bayesian inference of the equation of state that uses the
measured chirp mass and tidal deformability from GW170817 combined with nuclear
and astrophysical priors and discuss possible statistical biases in this
inference.Comment: Submitted to ApJ Letter
Selective interactions in trapped ions: state reconstruction and quantum logic
We propose the implementation of selective interactions of atom-motion
subspaces in trapped ions. These interactions yield resonant exchange of
population inside a selected subspace, leaving the others in a highly
dispersive regime. Selectivity allows us to generate motional Fock (and other
nonclassical) states with high purity out of a wide class of initial states,
and becomes an unconventional cooling mechanism when the ground state is
chosen. Individual population of number states can be distinctively measured,
as well as the motional Wigner function. Furthermore, a protocol for
implementing quantum logic through a suitable control of selective subspaces is
presented.Comment: 4 revtex4 pages and 2 eps figures. Submitted for publicatio
From Neutron Star Observables to the Equation of State. I. An Optimal Parametrization
The increasing number and precision of measurements of neutron star masses,
radii, and, in the near future, moments of inertia offer the possibility of
precisely determining the neutron star equation of state. One way to facilitate
the mapping of observables to the equation of state is through a
parametrization of the latter. We present here a generic method for optimizing
the parametrization of any physically allowed EoS. We use mock equations of
state that incorporate physically diverse and extreme behavior to test how well
our parametrization reproduces the global properties of the stars, by
minimizing the errors in the observables mass, radius, and the moment of
inertia. We find that using piecewise polytropes and sampling the EoS with five
fiducial densities between ~1-8 times the nuclear saturation density results in
optimal errors for the smallest number of parameters. Specifically, it
recreates the radii of the assumed EoS to within less than 0.5 km for the
extreme mock equations of state and to within less than 0.12 km for 95% of a
sample of 42 proposed, physically-motivated equations of state. Such a
parametrization is also able to reproduce the maximum mass to within 0.04 M_sun
and the moment of inertia of a 1.338 M_sun neutron star to within less than 10%
for 95% of the proposed sample of equations of state.Comment: Minor changes made to match published ApJ versio
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