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Neutron star

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
Milton Ruiz, Stuart L Shapiro, Antonios Tsokaros
Recent numerical simulations in general relativistic magnetohydrodynamics (GRMHD) provide useful constraints for the interpretation of the GW170817 discovery. Combining the observed data with these simulations leads to a bound on the maximum mass of a cold, spherical neutron star (the TOV limit): <mml:math xmlns:mml=""> <mml:mrow> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mo>max</mml:mo> <mml:mtext>sph</mml:mtext> </mml:msubsup> <mml:mo>≲</mml:mo> <mml:mn>2...
January 15, 2018: Physical Review. D
Milton Ruiz, Stuart L Shapiro
Inspiraling and merging binary neutron stars are not only important source of gravitational waves, but also promising candidates for coincident electromagnetic counterparts. These systems are thought to be progenitors of short gamma-ray bursts (sGRBs). We have shown previously that binary neutron star mergers that undergo delayed collapse to a black hole surrounded by a weighty magnetized accretion disk can drive magnetically powered jets. We now perform magnetohydrodynamic simulations in full general relativity of binary neutron stars mergers that undergo prompt collapse to explore the possibility of jet formation from black hole- light accretion disk remnants...
October 15, 2017: Physical Review. D
Lijing Shao, Norbert Wex, Michael Kramer
The violation of the weak equivalence principle (EP) in the gravitational field of Earth, described by the Eötvös parameter η_{⊕}, was recently constrained to the level |η_{⊕}|≲10^{-14} by the MICROSCOPE space mission. The Eötvös parameter η_{DM}, pertaining to the differential couplings of dark matter (DM) and ordinary matter, was only tested to the level |η_{DM}|≲10^{-5} by the Eöt-Wash group and lunar laser ranging. This test is limited by the EP-violating driving force in the solar neighborhood that is determined by the galactic distribution of DM...
June 15, 2018: Physical Review Letters
Davide Lazzati, Rosalba Perna, Brian J Morsony, Diego Lopez-Camara, Matteo Cantiello, Riccardo Ciolfi, Bruno Giacomazzo, Jared C Workman
The binary neutron star (BNS) merger GW170817 was the first astrophysical source detected in gravitational waves and multiwavelength electromagnetic radiation. The almost simultaneous observation of a pulse of gamma rays proved that BNS mergers are associated with at least some short gamma-ray bursts (GRBs). However, the gamma-ray pulse was faint, casting doubt on the association of BNS mergers with the luminous, highly relativistic outflows of canonical short GRBs. Here we show that structured jets with a relativistic, energetic core surrounded by slower and less energetic wings produce afterglow emission that brightens characteristically with time, as recently seen in the afterglow of GW170817...
June 15, 2018: Physical Review Letters
Roberto De Pietri, Alessandra Feo, José A Font, Frank Löffler, Francesco Maione, Michele Pasquali, Nikolaos Stergioulas
We present the first very long-term simulations (extending up to ∼140  ms after merger) of binary neutron star mergers with piecewise polytropic equations of state and in full general relativity. Our simulations reveal that, at a time of 30-50 ms after merger, parts of the star become convectively unstable, which triggers the excitation of inertial modes. The excited inertial modes are sustained up to several tens of milliseconds and are potentially observable by the planned third-generation gravitational-wave detectors at frequencies of a few kilohertz...
June 1, 2018: Physical Review Letters
Antonios Tsokaros, Milton Ruiz, Vasileios Paschalidis, Stuart L Shapiro, Luca Baiotti, Kōji Uryū
Targets for ground-based gravitational wave interferometers include continuous, quasiperiodic sources of gravitational radiation, such as isolated, spinning neutron stars. In this work, we perform evolution simulations of uniformly rotating, triaxially deformed stars, the compressible analogs in general relativity of incompressible, Newtonian Jacobi ellipsoids. We investigate their stability and gravitational wave emission. We employ five models, both normal and supramassive, and track their evolution with different grid setups and resolutions, as well as with two different evolution codes...
June 15, 2017: Physical Review. D
Raissa F P Mendes, Néstor Ortiz
Detection of the characteristic spectrum of pulsating neutron stars can be a powerful tool not only to probe the nuclear equation of state but also to test modifications to general relativity. However, the shift in the oscillation spectrum induced by modified theories of gravity is often small and degenerate with our ignorance of the equation of state. In this Letter, we show that the coupling to additional degrees of freedom present in modified theories of gravity can give rise to new families of modes, with no counterpart in general relativity, which could be sufficiently well resolved in frequency space to allow for clear detection...
May 18, 2018: Physical Review Letters
Kell Mortensen, Anine L Borger, Jacob J K Kirkensgaard, Christopher J Garvey, Kristoffer Almdal, Andriy Dorokhin, Qian Huang, Ole Hassager
We present structural small-angle neutron scattering studies of a three-armed polystyrene star polymer with short deuterated segments at the end of each arm. We show that the form factor of the three-armed star molecules in the relaxed state agrees with that of the random phase approximation of Gaussian chains. Upon exposure to large extensional flow conditions, the star polymers change conformation resulting in a highly stretched structure that mimics a fully extended three-armed tube model. All three arms are parallel to the flow, one arm being either in positive or negative stretching direction, while the two other arms are oriented parallel, right next to each other in the direction opposite to the first arm...
May 18, 2018: Physical Review Letters
Kyle Kremer, Sourav Chatterjee, Katelyn Breivik, Carl L Rodriguez, Shane L Larson, Frederic A Rasio
We explore the formation of double-compact-object binaries in Milky Way (MW) globular clusters (GCs) that may be detectable by the Laser Interferometer Space Antenna (LISA). We use a set of 137 fully evolved GC models that, overall, effectively match the properties of the observed GCs in the MW. We estimate that, in total, the MW GCs contain ∼21 sources that will be detectable by LISA. These detectable sources contain all combinations of black hole (BH), neutron star, and white dwarf components. We predict ∼7 of these sources will be BH-BH binaries...
May 11, 2018: Physical Review Letters
A Tumino, C Spitaleri, M La Cognata, S Cherubini, G L Guardo, M Gulino, S Hayakawa, I Indelicato, L Lamia, H Petrascu, R G Pizzone, S M R Puglia, G G Rapisarda, S Romano, M L Sergi, R Spartá, L Trache
Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars 1 (exceeding eight solar masses) and superbursts from accreting neutron stars2,3 . It proceeds through the 12 C + 12 C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23-that is, 12 C(12 C, α)20 Ne and 12 C(12 C, p)23 Na-at temperatures greater than 0.4 × 109 kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars...
May 2018: Nature
Edward F Brown, Andrew Cumming, Farrukh J Fattoyev, C J Horowitz, Dany Page, Sanjay Reddy
We show that the neutron star in the transient system MXB 1659-29 has a core neutrino luminosity that substantially exceeds that of the modified Urca reactions (i.e., n+n→n+p+e^{-}+ν[over ¯]_{e} and inverse) and is consistent with the direct Urca (n→p+e^{-}+ν[over ¯]_{e} and inverse) reaction occurring in a small fraction of the core. Observations of the thermal relaxation of the neutron star crust following 2.5 yr of accretion allow us to measure the energy deposited into the core during accretion, which is then reradiated as neutrinos, and infer the core temperature...
May 4, 2018: Physical Review Letters
Adrian Cho
No abstract text is available yet for this article.
May 18, 2018: Science
V D Burkert, L Elouadrhiri, F X Girod
The proton, one of the components of atomic nuclei, is composed of fundamental particles called quarks and gluons. Gluons are the carriers of the force that binds quarks together, and free quarks are never found in isolation-that is, they are confined within the composite particles in which they reside. The origin of quark confinement is one of the most important questions in modern particle and nuclear physics because confinement is at the core of what makes the proton a stable particle and thus provides stability to the Universe...
May 2018: Nature
Eemeli Annala, Tyler Gorda, Aleksi Kurkela, Aleksi Vuorinen
The detection of gravitational waves originating from a neutron-star merger, GW170817, by the LIGO and Virgo Collaborations has recently provided new stringent limits on the tidal deformabilities of the stars involved in the collision. Combining this measurement with the existence of two-solar-mass stars, we generate a generic family of neutron-star-matter equations of state (EOSs) that interpolate between state-of-the-art theoretical results at low and high baryon density. Comparing the results to ones obtained without the tidal-deformability constraint, we witness a dramatic reduction in the family of allowed EOSs...
April 27, 2018: Physical Review Letters
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