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Dark Matter constitutes most of the matter in the presently accepted cosmological model for our Universe. The extreme conditions of ordinary baryonic matter, namely high density and compactness, in Neutron Stars make these objects suitable to gravitationally accrete such a massive component provided interaction strength between both, luminous and dark sectors, at current experimental level of sensitivity. We consider several different DM phenomenological models from the myriad of those presently allowed. In this contribution, we review astrophysical aspects of interest in the interplay of ordinary matter and a fermionic light Dark Matter component. We focus in the interior nuclear medium in the core and external layers, i.e. the crust, discussing the impact of a novel dark sector in relevant stellar quantities for (heat) energy transport such as thermal conductivity or emissivities.
Galaxies are key elements of the universe. They probe cosmology, they control our existence. The broad lines of their formation and evolution are clear. Beginning as infinitesimal density fluctuations, in the early universe, leaving the observed relic pattern of temperature fluctuations on the last scattering surface of the CMB, galaxy halos grew via gravitational instability of cold weakly interacting dark matter, within which baryons dissipated and cooled into the observed galaxies. We are piecing together the missing steps, that involve assembly of massive halos from a hierarchy of merging subhalos.Memory remains in massive halos of the substructure forged by gravity: this has been one of the major revelations to come from computer simulations of structure formation in the expanding universe.
A major advance in demonstrating that galaxies formed via gravitational instability in the early universe came with the discovery of fine-scale angular fluctuations in the CMB. These were predicted as essential relics if galaxies had indeed formed by the conjectured instability. Prior to their discovery, one had no idea of the initial conditions for seeding structure formation. Thermal fluctuations in standard cosmology were known to be too small.
Observations provided the seeds. The breakthrough came with the COBE satellite in 1990. This provided the proof that temperature fluctuations are present and monitor the existence of large-scale density fluctuations. These had little to do, however, with the search for the precursors of galaxies, other than giving confidence that the latter are present under the assumption of a scale-invariant density fluctuation spectrum as advocated by inflationary cosmology.
The key theoretical insight indeed preceded the data. Inflationary cosmology was developed in the 1980s, and provided for the first time a coherent understanding of the size of the universe, its near-Euclidean geometry, and of the origin of the seed density fluctuations from quantum fluctuations at the Planck epoch. Even inflationary cosmology remains incomplete, since there is still no theory of quantum gravity required in order to connect Planck-scale physics rigorously with the Einstein–Friedmann–Lemaˆıtre cosmology that successfully describes the evolution of the universe. Such a connection is essential in order to understand the nature of the acceleration that couples inflation to the current acceleration of the universe, with an associated decrease in vacuum energy of some 120 orders of magnitude.
Cosmology is the unifying discipline par excellence, combining theories of gravity, thermodynamics, and quantum field theory with theories of structure formation, nuclear physics, and condensed matter physics. Its observational tools include the most intricate and expensive scientific experiments ever devised, from large-scale interferometry, highenergy particle accelerators, and deep-sea neutrino detectors, to space-based observatories such as Hubble, Wilkinson microwave anisotropy probe (WMAP) and Planck. The recent and stunning detection of massive gravitational encounters between black holes by means of gravitational waves is only one of several windows that have recently been opened into the study of distant and exotic objects, and to ever-earlier epochs of the universe.
Cosmology is in a golden age of discovery, the likes of which have rarely been seen in the physical sciences. Theory has hardly kept up, but its bringing together of the fundamental theories of physics is also historic in its vitality. It draws them together in ways that put pressure on each: whether because, as in quantum mechanics, cosmology is an application in which there is no ‘external observer’; or because, as with the standard model of particle physics and general relativity, there is tension between their basic principles; or because, as in statistical mechanics, it highlights the extraordinary importance of the initial conditions of the universe for local physics. Add to these components the existing foundational problems of each discipline even in non-cosmological settings: the measurement problem in quantum mechanics, the ‘naturalness’ problem of the Higgs mass and the cosmological constant or ‘dark energy’ (so-called ‘fine-tuning’ problems), and the information-loss paradox of black-hole physics. The result is a heady brew – and this is not even to mention the enigma that is dark matter, making up the bulk of the gravitating matter of the universe, its nature still unknown.
What place, in this perfect storm, for philosophy? Some see none: ‘philosophy is dead’, according to Stephen Hawking, and needs no engagement from scientists. And indeed, where philosophers of physics have made inroads on conceptual questions in physics, they have tended to focus on cleanly defined theories treated in isolation. Synthetic theories, in complex applications, are messy and ill suited to rigorous analysis, axiomatisation, or regimentation by other means – the standard tools of philosophy.
Following a long-term international collaboration between leaders in cosmology and the philosophy of science, this volume addresses foundational questions at the limit of science across these disciplines, questions raised by observational and theoretical progress in modern cosmology. Space missions have mapped the Universe up to its early instants, opening up questions on what came before the Big Bang, the nature of space and time, and the quantum origin of the Universe. As the foundational volume of an emerging academic discipline, experts from relevant fields lay out the fundamental problems of contemporary cosmology and explore the routes toward finding possible solutions. Written for graduates and researchers in physics and philosophy, particular efforts are made to inform academics from other fields, as well as the educated public, who wish to understand our modern vision of the Universe, related philosophical questions, and the significant impacts on scientific methodology.
We report a significant hardening of the Fermi-LAT gamma-ray spectrum from the core of Cen A at E > 2.4 GeV, suggesting there is a source of high energy particles in the core of Cen A which is in addition to the jet component. We show that the observed gamma-ray spectrum is compatible with either a spike in the dark matter halo profile or a population of millisecond pulsars. This work gives a strong indication of new gamma-ray production mechanisms in active galactic nuclei and could even provide evidence for the clustering of heavy dark matter particles around black holes.
Recent chemical abundance measurements of damped Lyman-alpha absorbers (DLAs) revealed a large intrinsic scatter in their metallicities. We discuss a semi-analytic model that was specifically designed to study this scatter by tracing the chemical evolution of the interstellar matter in small regions of the Universe with different mean density, from over- to underdense regions. It is shown that different histories of structure formation in these regions are reflected in the chemical properties of the proto-galaxies. We also address deuterium abundance measurements, which constitute a complementary probe of the star formation and infall histories.
Listeria monocytogenes is a foodborne pathogen that can cause bacteraemia, meningitis, and complications during pregnancy. In July 2012, molecular subtyping identified indistinguishable L. monocytogenes isolates from six patients and two samples of different cut and repackaged cheeses. A multistate outbreak investigation was initiated. Initial analyses identified an association between eating soft cheese and outbreak-related illness (odds ratio 17·3, 95% confidence interval 2·0–825·7) but no common brand. Cheese inventory data from locations where patients bought cheese and an additional location where repackaged cheese yielded the outbreak strain were compared to identify cheeses for microbiological sampling. Intact packages of imported ricotta salata yielded the outbreak strain. Fourteen jurisdictions reported 22 cases from March–October 2012, including four deaths and a fetal loss. Six patients ultimately reported eating ricotta salata; another reported eating cheese likely cut with equipment also used for contaminated ricotta salata, and nine more reported eating other cheeses that might also have been cross-contaminated. An FDA import alert and US and international recalls followed. Epidemiology-directed microbiological testing of suspect cheeses helped identify the outbreak source. Cross-contamination of cheese highlights the importance of using validated disinfectant protocols and routine cleaning and sanitizing after cutting each block or wheel.
The star formation history of galaxies is a complex process usually considered to be stochastic in nature, for which we can only give average descriptions such as the color-density relation. In this work we follow star-forming gas particles in a hydrodynamical N-body simulation back in time in order to study their initial spatial configuration. By keeping record of the time when a gas particle started forming stars we can produce Lagrangian gas-star isochrone surfaces delineating the surfaces of accreting gas that begin producing stars at different times. These surfaces form a complex a network of filaments in Eulerian space from which galaxies accrete cold gas. Lagrangian accretion surfaces are closely packed inside dense regions, intersecting each other, and as a result galaxies inside proto-clusters stop accreting gas early, naturally explaining the color dependence on density. The process described here has a purely gravitational / geometrical origin, arguably operating at a more fundamental level than complex processes such as AGN and supernovae, and providing a conceptual origin for the color-density relation.
We use a WISE-2MASS-Pan-STARRS1 galaxy catalog to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. We obtain photometric redshifts using our multicolor data set to create a tomographic map of the galaxy distribution. The radial density profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, 5°, and 15°. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large Rvoid=(192 ± 15)h−1 Mpc (2σ) supervoid with δ ≃ −0.13 ± 0.03 centered at z=0.22 ± 0.01. Such a supervoid, constituting a ∼3.5 σ fluctuation in the ΛCDM model, is a plausible cause for the Cold Spot.