40,551 research outputs found
Efficacy of crustal superfluid neutrons in pulsar glitch models
In order to assess the ability of purely crust-driven glitch models to match
the observed glitch activity in the Vela pulsar, we conduct a systematic
analysis of the dependence of the fractional moment of inertia of the inner
crustal neutrons on the stiffness of the nuclear symmetry energy at saturation
density . We take into account both crustal entrainment and the fact that
only a fraction of the core neutrons may couple to the crust on the
glitch-rise timescale. We use a set of consistently-generated crust and core
compositions and equations-of-state which are fit to results of low-density
pure neutron matter calculations. When entrainment is included at the level
suggested by recent microscopic calculations and the core is fully coupled to
the crust, the model is only able to account for the Vela glitch activity for a
1.4 star if the equation of state is particularly stiff MeV.
However, an uncertainty of about 10\% in the crust-core transition density and
pressure allows for the Vela glitch activity to be marginally accounted for in
the range MeV consistent with a range of experimental results.
Alternatively, only a small amount of core neutrons need be involved. If less
than 50\% of the core neutrons are coupled to the crust during the glitch, we
can also account for the Vela glitch activity using crustal neutrons alone for
EOSs consistent with the inferred range of . We also explore the possibility
of Vela being a high-mass neutron star, and of crustal entrainment being
reduced or enhanced relative to its currently predicted values.Comment: 10 pages, 6 figure
Probing the high-density behavior of symmetry energy with gravitational waves
Gravitational wave (GW) astronomy opens up an entirely new window on the
Universe to probe the equations of state (EOS) of neutron-rich matter. With the
advent of next generation GW detectors, measuring the gravitational radiation
from coalescing binary neutron star systems, mountains on rotating neutron
stars, and stellar oscillation modes may become possible in the near future.
Using a set of model EOSs satisfying the latest constraints from terrestrial
nuclear experiments, state of the art nuclear many-body calculations of the
pure neutron matter EOS, and astrophysical observations consistently, we study
various GW signatures of the high-density behavior of the nuclear symmetry
energy, which is considered among the most uncertain properties of dense
neutron-rich nucleonic matter. In particular, we find the tidal polarizability
of neutron stars, potentially measurable in binary systems just prior to
merger, is more sensitive to the high density component of the nuclear symmetry
energy than the symmetry energy at nuclear saturation density. We also find
that the upper limit on the GW strain amplitude from elliptically deformed
stars is very sensitive to the density dependence of the symmetry energy. This
suggests that future developments in modeling of the neutron star crust, and
direct gravitational wave signals from accreting binaries will provide a wealth
of information on the EOS of neutron-rich matter. We also review the
sensitivity of the -mode instability window to the density dependence of the
symmetry energy. Whereas models with larger values of the density slope of the
symmetry energy at saturation seem to be disfavored by the current
observational data, within a simple -mode model, we point out that a
subsequent softer behavior of the symmetry energy at high densities (hinted at
by recent observational interpretations) could rule them in.Comment: 14 pages, 11 figures, 3 tables; submitted to EPJA Special Volume on
Nuclear Symmetry Energ
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