Implications for compact stars of a soft nuclear equation of state from heavy-ion data. (arXiv:1211.0427v1 [astro-ph.HE]):
We study the implications on compact star properties of a soft nuclear
equation of state determined from kaon production at subthreshold energies in
heavy-ion collisions. On one hand, we apply these results to study radii and
moments of inertia of light neutron stars. Heavy-ion data provides constraints
on nuclear matter at densities relevant for those stars and, in particular, to
the density dependence of the symmetry energy of nuclear matter. On the other
hand, we derive a limit for the highest allowed neutron star mass of three
solar masses. For that purpose, we use the information on the nucleon potential
obtained from the analysis of the heavy-ion data combined with causality on the
nuclear equation of state.
Friday, November 9, 2012
Large Synoptic Survey Telescope: Dark Energy Science Collaboration. (arXiv:1211.0310v1 [astro-ph.CO])
Large Synoptic Survey Telescope: Dark Energy Science Collaboration. (arXiv:1211.0310v1 [astro-ph.CO]):
This white paper describes the LSST Dark Energy Science Collaboration (DESC),
whose goal is the study of dark energy and related topics in fundamental
physics with data from the Large Synoptic Survey Telescope (LSST). It provides
an overview of dark energy science and describes the current and anticipated
state of the field. It makes the case for the DESC by laying out a robust
analytical framework for dark energy science that has been defined by its
members and the comprehensive three-year work plan they have developed for
implementing that framework. The analysis working groups cover five key probes
of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia
supernovae, and strong lensing. The computing working groups span cosmological
simulations, galaxy catalogs, photon simulations and a systematic software and
computational framework for LSST dark energy data analysis. The technical
working groups make the connection between dark energy science and the LSST
system. The working groups have close linkages, especially through the use of
the photon simulations to study the impact of instrument design and survey
strategy on analysis methodology and cosmological parameter estimation. The
white paper describes several high priority tasks identified by each of the 16
working groups. Over the next three years these tasks will help prepare for
LSST analysis, make synergistic connections with ongoing cosmological surveys
and provide the dark energy community with state of the art analysis tools.
Members of the community are invited to join the LSST DESC, according to the
membership policies described in the white paper. Applications to sign up for
associate membership may be made by submitting the Web form at
this http URL with a short statement
of the work they wish to pursue that is relevant to the LSST DESC.
This white paper describes the LSST Dark Energy Science Collaboration (DESC),
whose goal is the study of dark energy and related topics in fundamental
physics with data from the Large Synoptic Survey Telescope (LSST). It provides
an overview of dark energy science and describes the current and anticipated
state of the field. It makes the case for the DESC by laying out a robust
analytical framework for dark energy science that has been defined by its
members and the comprehensive three-year work plan they have developed for
implementing that framework. The analysis working groups cover five key probes
of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia
supernovae, and strong lensing. The computing working groups span cosmological
simulations, galaxy catalogs, photon simulations and a systematic software and
computational framework for LSST dark energy data analysis. The technical
working groups make the connection between dark energy science and the LSST
system. The working groups have close linkages, especially through the use of
the photon simulations to study the impact of instrument design and survey
strategy on analysis methodology and cosmological parameter estimation. The
white paper describes several high priority tasks identified by each of the 16
working groups. Over the next three years these tasks will help prepare for
LSST analysis, make synergistic connections with ongoing cosmological surveys
and provide the dark energy community with state of the art analysis tools.
Members of the community are invited to join the LSST DESC, according to the
membership policies described in the white paper. Applications to sign up for
associate membership may be made by submitting the Web form at
this http URL with a short statement
of the work they wish to pursue that is relevant to the LSST DESC.
Black hole mergers: do gas discs lead to spin alignment?. (arXiv:1211.0284v1 [astro-ph.CO])
Black hole mergers: do gas discs lead to spin alignment?. (arXiv:1211.0284v1 [astro-ph.CO]):
In this Letter we revisit arguments suggesting that the Bardeen-Petterson
effect can coalign the spins of a central supermassive black hole binary
accreting from a circumbinary (or circumnuclear) gas disc. We improve on
previous estimates by adding the dependence on system parameters, and noting
that the nonlinear nature of warp propagation in a thin viscous disc affects
alignment. This reduces the disc's ability to communicate the warp, and can
severely reduce the effectiveness of disc-assisted spin alignment. We test our
predictions with a Monte Carlo realization of random misalignments and
accretion rates and we find that the outcome depends strongly on the spin
magnitude. We estimate a generous upper limit to the probability of alignment
by making assumptions which favour it throughout. Even with these assumptions,
about 40% of black holes with $a \gtrsim 0.5$ do not have time to align with
the disc. If the residual misalignment is not small and it is maintained down
to the final coalescence phase this can give a powerful recoil velocity to the
merged hole. Highly spinning black holes are thus more likely of being subject
to strong recoils, the occurrence of which is currently debated.
In this Letter we revisit arguments suggesting that the Bardeen-Petterson
effect can coalign the spins of a central supermassive black hole binary
accreting from a circumbinary (or circumnuclear) gas disc. We improve on
previous estimates by adding the dependence on system parameters, and noting
that the nonlinear nature of warp propagation in a thin viscous disc affects
alignment. This reduces the disc's ability to communicate the warp, and can
severely reduce the effectiveness of disc-assisted spin alignment. We test our
predictions with a Monte Carlo realization of random misalignments and
accretion rates and we find that the outcome depends strongly on the spin
magnitude. We estimate a generous upper limit to the probability of alignment
by making assumptions which favour it throughout. Even with these assumptions,
about 40% of black holes with $a \gtrsim 0.5$ do not have time to align with
the disc. If the residual misalignment is not small and it is maintained down
to the final coalescence phase this can give a powerful recoil velocity to the
merged hole. Highly spinning black holes are thus more likely of being subject
to strong recoils, the occurrence of which is currently debated.
A low-scatter survey-based mass proxy for clusters of galaxies. (arXiv:1211.0790v1 [astro-ph.CO])
A low-scatter survey-based mass proxy for clusters of galaxies. (arXiv:1211.0790v1 [astro-ph.CO]):
Estimates of cosmological parameters using galaxy clusters have the scatter
in the observable at a given mass as a fundamental parameter. This work
computes the amplitude of the scatter for a newly introduced mass proxy, the
product of the cluster total luminosity times the mass-to-light ratio, usually
referred as stellar mass. The analysis of 12 galaxy clusters with excellent
total masses shows a tight correlation between the stellar mass, or stellar
fraction, and total mass within r500 with negligible intrinsic scatter: the 90%
upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is
similar to the one of best-determined mass proxies, such as Yx, i.e. the
product of X-ray temperature and gas mass. The size of the cluster sample used
to determine the intrinsic scatter is small, as in previous works proposing
low-scatter proxies because very accurate masses are needed to infer very small
values of intrinsic scatter. Three-quarters of the studied clusters have lgM
<~14 Msol, which is advantageous from a cosmological perspective because these
clusters are far more abundant than more massive clusters. At the difference of
other mass proxies such as Yx, stellar mass can be determined with survey data
up to at least z=0.9 using upcoming optical near-infrared surveys, such as DES
and Euclid, or even with currently available surveys, covering however smaller
solid angles. On the other end, the uncertainty about the predicted mass of a
single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This
is largely because the proxy itself has ~0.10 dex errors for clusters of lgM<~
14 Msol mass.
Estimates of cosmological parameters using galaxy clusters have the scatter
in the observable at a given mass as a fundamental parameter. This work
computes the amplitude of the scatter for a newly introduced mass proxy, the
product of the cluster total luminosity times the mass-to-light ratio, usually
referred as stellar mass. The analysis of 12 galaxy clusters with excellent
total masses shows a tight correlation between the stellar mass, or stellar
fraction, and total mass within r500 with negligible intrinsic scatter: the 90%
upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is
similar to the one of best-determined mass proxies, such as Yx, i.e. the
product of X-ray temperature and gas mass. The size of the cluster sample used
to determine the intrinsic scatter is small, as in previous works proposing
low-scatter proxies because very accurate masses are needed to infer very small
values of intrinsic scatter. Three-quarters of the studied clusters have lgM
<~14 Msol, which is advantageous from a cosmological perspective because these
clusters are far more abundant than more massive clusters. At the difference of
other mass proxies such as Yx, stellar mass can be determined with survey data
up to at least z=0.9 using upcoming optical near-infrared surveys, such as DES
and Euclid, or even with currently available surveys, covering however smaller
solid angles. On the other end, the uncertainty about the predicted mass of a
single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This
is largely because the proxy itself has ~0.10 dex errors for clusters of lgM<~
14 Msol mass.
On the Hot Gas Content of the Milky Way Halo. (arXiv:1211.0758v1 [astro-ph.CO])
On the Hot Gas Content of the Milky Way Halo. (arXiv:1211.0758v1 [astro-ph.CO]):
The Milky Way appears to be missing baryons, as the observed mass in stars
and gas is well below the cosmic mean. One possibility is that a substantial
fraction of the Galaxy's baryons are embedded within an extended,
million-degree hot halo, an idea supported indirectly by observations of warm
gas clouds in the halo and gas-free dwarf spheroidal satellites. X-ray
observations have established that hot gas does exist in our Galaxy beyond the
local hot bubble; however, it may be distributed in a hot disk configuration.
Moreover, recent investigations into the X-ray constraints have suggested that
any Galactic corona must be insignificant. Here we re-examine the observational
data, particularly in the X-ray and radio bands, in order to determine whether
it is possible for a substantial fraction of the Galaxy's baryons to exist in ~
10^6 K gas. In agreement with past studies, we find that a baryonically closed
halo is clearly ruled out if one assumes that the hot corona is distributed
with a cuspy NFW profile. However, if the hot corona of the galaxy is in an
extended, low-density distribution with a large central core, as expected for
an adiabatic gas in hydrostatic equilibrium, then it may contain up to 10^11
M_sun of material, possibly accounting for all of the missing Galactic baryons.
We briefly discuss some potential avenues for discriminating between a massive,
extended hot halo and a local hot disk.
The Milky Way appears to be missing baryons, as the observed mass in stars
and gas is well below the cosmic mean. One possibility is that a substantial
fraction of the Galaxy's baryons are embedded within an extended,
million-degree hot halo, an idea supported indirectly by observations of warm
gas clouds in the halo and gas-free dwarf spheroidal satellites. X-ray
observations have established that hot gas does exist in our Galaxy beyond the
local hot bubble; however, it may be distributed in a hot disk configuration.
Moreover, recent investigations into the X-ray constraints have suggested that
any Galactic corona must be insignificant. Here we re-examine the observational
data, particularly in the X-ray and radio bands, in order to determine whether
it is possible for a substantial fraction of the Galaxy's baryons to exist in ~
10^6 K gas. In agreement with past studies, we find that a baryonically closed
halo is clearly ruled out if one assumes that the hot corona is distributed
with a cuspy NFW profile. However, if the hot corona of the galaxy is in an
extended, low-density distribution with a large central core, as expected for
an adiabatic gas in hydrostatic equilibrium, then it may contain up to 10^11
M_sun of material, possibly accounting for all of the missing Galactic baryons.
We briefly discuss some potential avenues for discriminating between a massive,
extended hot halo and a local hot disk.
X-ray Spectroscopy of Clusters of Galaxies. (arXiv:1211.0679v1 [astro-ph.CO])
X-ray Spectroscopy of Clusters of Galaxies. (arXiv:1211.0679v1 [astro-ph.CO]):
Clusters of galaxies are the most massive objects in the Universe and precise
knowledge of their mass structure is important to understand the history of
structure formation and constrain still unknown types of dark contents of the
Universe. X-ray spectroscopy of galaxy clusters provides rich information about
the physical state of hot intracluster gas and the underlying potential
structure. In this paper, starting from the basic description of clusters under
equilibrium conditions, we review properties of clusters revealed primarily
through X-ray observations considering their thermal and dynamical evolutions.
The future prospects of cluster studies using upcoming X-ray missions are also
mentioned.
Clusters of galaxies are the most massive objects in the Universe and precise
knowledge of their mass structure is important to understand the history of
structure formation and constrain still unknown types of dark contents of the
Universe. X-ray spectroscopy of galaxy clusters provides rich information about
the physical state of hot intracluster gas and the underlying potential
structure. In this paper, starting from the basic description of clusters under
equilibrium conditions, we review properties of clusters revealed primarily
through X-ray observations considering their thermal and dynamical evolutions.
The future prospects of cluster studies using upcoming X-ray missions are also
mentioned.
Maximum mass of neutron stars and strange neutron-star cores. (arXiv:1211.1231v1 [astro-ph.SR])
Maximum mass of neutron stars and strange neutron-star cores. (arXiv:1211.1231v1 [astro-ph.SR]):
Recent measurement of mass of PSR J1614-2230 rules out most of existing
models of equation of state (EOS) of dense matter with high-density softening
due to hyperonization, based on the recent hyperon-nucleon and hyperon-hyperon
interactions, leading to a "hyperon puzzle".
We study a specific solution of "hyperon puzzle", consisting in replacing a
too soft hyperon core by a sufficiently stiff quark core. We construct an
analytic approximation fitting very well modern EOSs of 2SC and CFL color
superconducting phases of quark matter. This allows us for simulating continua
of sequences of first-order phase transitions from hadronic matter to the 2SC,
and then to the CFL state of color superconducting quark matter.
We obtain constraints in the parameter space of the EOS of superconducting
quark cores, resulting from M_max> 2 M_sol. We also derive constraints that
would result from significantly higher measured masses. For 2.4 M_sol required
stiffness of the CFL quark core should have been close to the causality limit,
the density jump at the phase transition being very small.
Condition M_max > 2 M_sol puts strong constraints on the EOSs of the 2SC and
CFL phases of quark matter. Density jumps at the phase transitions have to be
sufficiently small and sound speeds in quark matter - sufficiently large. A
strict condition of thermodynamic stability of quark phase results in the
maximum mass of hybrid stars similar to that of purely baryon stars. Therefore,
to get M_max>2 M_sol for stable hybrid stars, both sufficiently strong
additional hyperon repulsion at high density baryon matter and a sufficiently
stiff EOS of quark matter would be needed. However, it is likely that the high
density instability of quark matter (reconfinement) indicates actually the
inadequacy of the point-particle model of baryons in dense matter at very high
densities.
Recent measurement of mass of PSR J1614-2230 rules out most of existing
models of equation of state (EOS) of dense matter with high-density softening
due to hyperonization, based on the recent hyperon-nucleon and hyperon-hyperon
interactions, leading to a "hyperon puzzle".
We study a specific solution of "hyperon puzzle", consisting in replacing a
too soft hyperon core by a sufficiently stiff quark core. We construct an
analytic approximation fitting very well modern EOSs of 2SC and CFL color
superconducting phases of quark matter. This allows us for simulating continua
of sequences of first-order phase transitions from hadronic matter to the 2SC,
and then to the CFL state of color superconducting quark matter.
We obtain constraints in the parameter space of the EOS of superconducting
quark cores, resulting from M_max> 2 M_sol. We also derive constraints that
would result from significantly higher measured masses. For 2.4 M_sol required
stiffness of the CFL quark core should have been close to the causality limit,
the density jump at the phase transition being very small.
Condition M_max > 2 M_sol puts strong constraints on the EOSs of the 2SC and
CFL phases of quark matter. Density jumps at the phase transitions have to be
sufficiently small and sound speeds in quark matter - sufficiently large. A
strict condition of thermodynamic stability of quark phase results in the
maximum mass of hybrid stars similar to that of purely baryon stars. Therefore,
to get M_max>2 M_sol for stable hybrid stars, both sufficiently strong
additional hyperon repulsion at high density baryon matter and a sufficiently
stiff EOS of quark matter would be needed. However, it is likely that the high
density instability of quark matter (reconfinement) indicates actually the
inadequacy of the point-particle model of baryons in dense matter at very high
densities.
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