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Neutron star

M E Caplan, A S Schneider, C J Horowitz
The elastic properties of neutron star crusts are relevant for a variety of currently observable or near-future electromagnetic and gravitational wave phenomena. These phenomena may depend on the elastic properties of nuclear pasta found in the inner crust. We present large-scale classical molecular dynamics simulations where we deform nuclear pasta. We simulate idealized samples of nuclear pasta and describe their breaking mechanism. We also deform nuclear pasta that is arranged into many domains, similar to what is known for the ions in neutron star crusts...
September 28, 2018: Physical Review Letters
Thomas M Tauris
The prime candidate sources for the upcoming space-borne gravitational wave (GW) observatory LISA are the numerous Galactic tight binaries of white dwarfs (WDs) and neutron stars (NSs), many of which will coalesce and undergo mass transfer, leading to simultaneous emission of x rays and GWs. Here, detailed and coherent numerical stellar models are explored for the formation and evolution of these systems, including finite-temperature effects and complete calculations of mass transfer from a WD to a NS accretor...
September 28, 2018: Physical Review Letters
K De, M M Kasliwal, E O Ofek, T J Moriya, J Burke, Y Cao, S B Cenko, G B Doran, G E Duggan, R P Fender, C Fransson, A Gal-Yam, A Horesh, S R Kulkarni, R R Laher, R Lunnan, I Manulis, F Masci, P A Mazzali, P E Nugent, D A Perley, T Petrushevska, A L Piro, C Rumsey, J Sollerman, M Sullivan, F Taddia
Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor...
October 12, 2018: Science
Erkan Senses, Madhusudan Tyagi, Madeleine Pasco, Antonio Faraone
We present nanocomposite materials formed by using glassy star-shaped polymers as nanofillers and dispersing them in soft matrices. The resulting 'architecturally engineered' polymer nanocomposites structurally reside between the linear homopolymer blends and the conventional polymer nanocomposites with inorganic fillers, inducing reinforcement, which can be as strong as that of solid nanoparticles, or softening depending on the compactness and concentration of the nanoparticles. Such behavior can be traced back to the dynamical features at the local segmental and the chain level, which we investigated using neutron scattering over a wide range of time and length-scales in the glassy and melt states of the nanocomposites...
October 9, 2018: ACS Nano
A U Abeysekara, A Albert, R Alfaro, C Alvarez, J D Álvarez, R Arceo, J C Arteaga-Velázquez, D Avila Rojas, H A Ayala Solares, E Belmont-Moreno, S Y BenZvi, C Brisbois, K S Caballero-Mora, T Capistrán, A Carramiñana, S Casanova, M Castillo, U Cotti, J Cotzomi, S Coutiño de León, C De León, E De la Fuente, J C Díaz-Vélez, S Dichiara, B L Dingus, M A DuVernois, R W Ellsworth, K Engel, C Espinoza, K Fang, H Fleischhack, N Fraija, A Galván-Gámez, J A García-González, F Garfias, A González-Muñoz, M M González, J A Goodman, Z Hampel-Arias, J P Harding, S Hernandez, J Hinton, B Hona, F Hueyotl-Zahuantitla, C M Hui, P Hüntemeyer, A Iriarte, A Jardin-Blicq, V Joshi, S Kaufmann, P Kar, G J Kunde, R J Lauer, W H Lee, H León Vargas, H Li, J T Linnemann, A L Longinotti, G Luis-Raya, R López-Coto, K Malone, S S Marinelli, O Martinez, I Martinez-Castellanos, J Martínez-Castro, J A Matthews, P Miranda-Romagnoli, E Moreno, M Mostafá, A Nayerhoda, L Nellen, M Newbold, M U Nisa, R Noriega-Papaqui, J Pretz, E G Pérez-Pérez, Z Ren, C D Rho, C Rivière, D Rosa-González, M Rosenberg, E Ruiz-Velasco, F Salesa Greus, A Sandoval, M Schneider, H Schoorlemmer, M Seglar Arroyo, G Sinnis, A J Smith, R W Springer, P Surajbali, I Taboada, O Tibolla, K Tollefson, I Torres, G Vianello, L Villaseñor, T Weisgarber, F Werner, S Westerhoff, J Wood, T Yapici, G Yodh, A Zepeda, H Zhang, H Zhou
SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star)1-3 . Two jets of ionized matter with a bulk velocity of approximately 0.26c (where c is the speed of light in vacuum) extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets2,4-8 . SS 433 differs from other microquasars (small-scale versions of quasars that are present within our own Galaxy) in that the accretion is believed to be super-Eddington9-11 , and the luminosity of the system is about 1040 ergs per second2,9,12,13 ...
October 2018: Nature
J van den Eijnden, N Degenaar, T D Russell, R Wijnands, J C A Miller-Jones, G R Sivakoff, J V Hernández Santisteban
Relativistic jets are observed throughout the Universe and strongly affect their surrounding environments on a range of physical scales, from Galactic binary systems1 to galaxies and clusters of galaxies2 . All types of accreting black hole and neutron star have been observed to launch jets3 , with the exception of neutron stars with strong magnetic fields4,5 (higher than 1012 gauss), leading to the conclusion that their magnetic field strength inhibits jet formation6 . However, radio emission recently detected from two such objects could have a jet origin, among other possible explanations7,8 , indicating that this long-standing idea might need to be reconsidered...
October 2018: Nature
L Contessi, N Barnea, A Gal
We address the Λ hypernuclear "overbinding problem" in light hypernuclei which stands for a 1-3 MeV excessive Λ separation energy calculated in _{Λ}^{5}He. This problem arises in most few-body calculations that reproduce ground-state Λ separation energies in the lighter Λ hypernuclei within various hyperon-nucleon interaction models. Recent pionless effective field theory (πEFT) nuclear few-body calculations are extended in this work to Λ hypernuclei. At leading order, the ΛN low-energy constants are associated with ΛN scattering lengths, and the ΛNN low-energy constants are fitted to Λ separation energies (B_{Λ}^{exp}) for A≤4...
September 7, 2018: Physical Review Letters
Soumi De, Daniel Finstad, James M Lattimer, Duncan A Brown, Edo Berger, Christopher M Biwer
We use gravitational-wave observations of the binary neutron star merger GW170817 to explore the tidal deformabilities and radii of neutron stars. We perform a Bayesian parameter estimation with the source location and distance informed by electromagnetic observations. We also assume that the two stars have the same equation of state; we demonstrate that, for stars with masses comparable to the component masses of GW170817, this is effectively implemented by assuming that the stars' dimensionless tidal deformabilities are determined by the binary's mass ratio q by Λ_{1}/Λ_{2}=q^{6}...
August 31, 2018: Physical Review Letters
K P Mooley, A T Deller, O Gottlieb, E Nakar, G Hallinan, S Bourke, D A Frail, A Horesh, A Corsi, K Hotokezaka
The binary neutron-star merger GW1708171 was accompanied by radiation across the electromagnetic spectrum2 and localized2 to the galaxy NGC 4993 at a distance3 of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset4-7 , a gradual increase8 in the emission with time (proportional to t0.8 ) to a peak about 150 days after the merger event9 , followed by a relatively rapid decline9,10 . So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon4,8,11-13 and a successful-jet cocoon4,8,11-18 (also called a structured jet)...
September 5, 2018: Nature
Huan Yang, Denis Martynov
Gravitational memory is an important prediction of General Relativity, which is intimately related to asymptotic symmetries at null infinity and the so-called soft graviton theorem. For a given transient astronomical event, the angular distribution of energy and angular momentum fluxes uniquely determine the displacement and spin memory effect in the sky. We investigate the possibility of using the binary black hole merger events detected by Advanced LIGO/Virgo to test the relation between the source's energy emission and the gravitational memory measured on Earth, as predicted by General Relativity...
August 17, 2018: Physical Review Letters
A Kievsky, M Viviani, D Logoteta, I Bombaci, L Girlanda
The large values of the singlet and triplet two-nucleon scattering lengths locate the nuclear system close to the unitary limit. This particular position strongly constrains the low-energy observables in the three-nucleon system as depending on one parameter, the triton binding energy, and introduces correlations in the low-energy sector of light nuclei. Here we analyze the propagation of these correlations to infinite nuclear matter showing that its saturation properties, the equation of state of β-stable nuclear matter, and several properties of neutron stars, as their maximum mass, are well determined solely by a few number of low-energy quantities of the two- and three-nucleon systems...
August 17, 2018: Physical Review Letters
Gordon Baym, D H Beck, Peter Geltenbort, Jessie Shelton
The observation of neutron stars with masses greater than one solar mass places severe demands on any exotic neutron decay mode that could explain the discrepancy between beam and bottle measurements of the neutron lifetime. If the neutron can decay to a stable, feebly interacting dark fermion, the maximum possible mass of a neutron star is 0.7M_{⊙}, while all well-measured neutron star masses exceed one M_{⊙}. The existence of 2M_{⊙} neutron stars further indicates that any explanation beyond the standard model for the neutron lifetime puzzle requires dark matter to be part of a multiparticle dark sector with highly constrained interactions...
August 10, 2018: Physical Review Letters
David McKeen, Ann E Nelson, Sanjay Reddy, Dake Zhou
Exotic particles carrying baryon number and with a mass of the order of the nucleon mass have been proposed for various reasons including baryogenesis, dark matter, mirror worlds, and the neutron lifetime puzzle. We show that the existence of neutron stars with a mass greater than 0.7  M_{⊙} places severe constraints on such particles, requiring them to be heavier than 1.2 GeV or to have strongly repulsive self-interactions.
August 10, 2018: Physical Review Letters
Yeunhwan Lim, Jeremy W Holt
We confront observational data from gravitational wave event GW170817 with microscopic modeling of the cold neutron star equation of state. We develop and employ a Bayesian statistical framework that enables us to implement constraints on the equation of state from laboratory measurements of nuclei and state-of-the-art chiral effective field theory methods. The energy density functionals constructed from the posterior probability distributions are then used to compute consistently the neutron star equation of state from the outer crust to the inner core, assuming a composition consisting of protons, neutrons, electrons, and muons...
August 10, 2018: Physical Review Letters
Matthew D Duez, Yosef Zlochower
We review the dramatic progress in the simulations of compact objects and compact-object binaries that has taken place in the first two decades of the twenty-first century. This includes simulations of the inspirals and violent mergers of binaries containing black holes and neutron stars, as well as simulations of black-hole formation through failed supernovae and high-mass neutron star--neutron star mergers. Modeling such events requires numerical integration of the field equations of general relativity in three spatial dimensions, coupled, in the case of neutron-star containing binaries, with increasingly sophisticated treatment of fluids, electromagnetic fields, and neutrino radiation...
August 17, 2018: Reports on Progress in Physics
Kalin V Staykov, Dimitar Popchev, Daniela D Doneva, Stoytcho S Yazadjiev
Binary pulsar observations and gravitational wave detections seriously constrained scalar-tensor theories with massless scalar field allowing only small deviations from general relativity. If we consider a nonzero mass of the scalar field, though, significant deviations from general relativity are allowed for values of the parameters that are in agreement with the observations. In the present paper we extend this idea and we study scalar-tensor theory with massive field with self-interaction term in the potential...
2018: European Physical Journal. C, Particles and Fields
Salvatore Vitale, Hsin-Yu Chen
The detection of GW170817 and the identification of its host galaxy have allowed for the first standard-siren measurement of the Hubble constant, with an uncertainty of ∼14%. As more detections of binary neutron stars with redshift measurement are made, the uncertainty will shrink. The dominating factors will be the number of joint detections and the uncertainty on the luminosity distance of each event. Neutron star black hole mergers are also promising sources for advanced LIGO and Virgo. If the black hole spin induces precession of the orbital plane, the degeneracy between luminosity distance and the orbital inclination is broken, leading to a much better distance measurement...
July 13, 2018: Physical Review Letters
Qi Zhong, Lei Mi, Ezzeldin Metwalli, Lorenz Bießmann, Martine Philipp, Anna Miasnikova, Andre Laschewsky, Christine M Papadakis, Robert Cubitt, Matthias Schwartzkopf, Stephan V Roth, Jiping Wang, Peter Müller-Buschbaum
The effect of chain architecture on the swelling and thermal response of thin films obtained from an amphiphilic three-arm star-shaped thermo-responsive block copolymer poly(methoxy diethylene glycol acrylate)-block-polystyrene ((PMDEGA-b-PS)3 ) is investigated by in situ neutron reflectivity (NR) measurements. The PMDEGA and PS blocks are micro-phase separated with randomly distributed PS nanodomains. The (PMDEGA-b-PS)3 films show a transition temperature (TT) at 33 °C in white light interferometry. The swelling capability of the (PMDEGA-b-PS)3 films in a D2 O vapor atmosphere is better than that of films from linear PS-b-PMDEGA-b-PS triblock copolymers, which can be attributed to the hydrophilic end groups and limited size of the PS blocks in (PMDEGA-b-PS)3 ...
August 21, 2018: Soft Matter
R Orford, N Vassh, J A Clark, G C McLaughlin, M R Mumpower, G Savard, R Surman, A Aprahamian, F Buchinger, M T Burkey, D A Gorelov, T Y Hirsh, J W Klimes, G E Morgan, A Nystrom, K S Sharma
The Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility was used to measure the masses of eight neutron-rich isotopes of Nd and Sm. These measurements are the first to push into the region of nuclear masses relevant to the formation of the rare-earth abundance peak at A∼165 by the rapid neutron-capture process. We compare our results with theoretical predictions obtained from "reverse engineering" the mass surface that best reproduces the observed solar abundances in this region through a Markov chain Monte Carlo technique...
June 29, 2018: Physical Review Letters
Elias R Most, Lukas R Weih, Luciano Rezzolla, Jürgen Schaffner-Bielich
We explore in a parameterized manner a very large range of physically plausible equations of state (EOSs) for compact stars for matter that is either purely hadronic or that exhibits a phase transition. In particular, we produce two classes of EOSs with and without phase transitions, each containing one million EOSs. We then impose constraints on the maximum mass (M<2.16  M_{⊙}) and on the dimensionless tidal deformability (Λ[over ˜]<800) deduced from GW170817, together with recent suggestions of lower limits on Λ[over ˜]...
June 29, 2018: Physical Review Letters
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