Rapidly rotating neutron stars with realistic nuclear matter equation of state

We performed a comparison of three different numerical codes for constructing equilibrium models; (I) a code for static equilibrium configurations, (II) an implementation of the Hartle--Thorne slow-rotation approximation, (III) a numerical solution of the full Einstein equations by \texttt{LORENE}. We aimed to construct sequences of uniformly rotating configurations at various rotation frequencies up to the Keplerian frequency for a hybrid hadronic--quark matter EOS where a smooth transition is provided between two separate phases. We investigated the difference of between the results computed by the implementation of Hartle--Thorne slow-rotation approximation and by \texttt{LORENE/nrotstar}, respectively. We have conclude that the codes can the difference between the slow rotating and the fast-rotating approach increase exponentially, reaching 6.67% for the maximal mass configuration rotating at the Keplerian frequency.Comment: 7 pages, 4 figures, conference proceedin

Gravitációs hullámkeltési folyamatok vizsgálata az általános relativitáselméletben = Study of gravitational wave production in general relativity

A kutatási terveinknek megfelelően az alábbi nyolc területen értünk el eredményeket: I. A nemlineáris gömbszimmetrikus dinamikai rendszerek időfejlődését hűen leíró numerikus eljárásunkat továbbfejlesztettük úgy, hogy mind az szimmetriafeltételektől mentes rendszerek leírására, mind pedig az „adaptív rácsfinomításos” technikai elemek alkalmazására képes legyen. A fejlesztésekkel párhuzamosan különféle általános relativisztikus dinamikai rendszer időfejlődését határoztuk meg. II. Feltártuk a gravitációs összeomlási folyamatok során kialakuló dinamikai feketelyuk-téridők topológiai tulajdonságait. III. A gravitáció geometrizált elméleteiben megadtuk a szinguláris téridők globális kiterjeszthetőségének szükséges feltételeit. IV. Fizikailag reális állapotegyenletű forgó neutroncsillag-modellek megkonstruálása. V. Gömbszimmetrikus csillagmodellek vizsgálata a nem zérus kozmológiai állandóval jellemzett univerzummodellek esetén. VI. Neutroncsillag-modellek stabilitásvizsgálata, valamint a gömbhéjakba tömörülő anyageloszlások általános dinamikájának leírása. VII. A deformált stacionárius feketelyuk-téridők általános leírása. VIII. Részvétel a Virgo tudományos együttműködés munkájában és a CBwaves nevű programcsomag kidolgozása és a LIGO-Virgo együttműködés által alkalmazott keresőalgoritmusokba történő integrálása. A pályázatban megjelölt feladatokhoz kapcsolódóan 14 elméleti témájú, és 23 kollaborációs, magas impaktfaktorú folyóiratcikkünk jelent meg. | In accordance with our research proposal the new results belong to either of the following eight categories: I. Our numerical method capable to follow the time evolution of generic spherically symmetric dynamical systems was further developed such that both the symmetry assumptions were relaxed and the techniques of adaptive mesh refinements had been implemented. In parallel the developed code had been applied to study the evolution of various general relativistic dynamical systems. II. The topological properties of generic co-dimension two surfaces in black hole spacetime was determined. III. In metric theories of gravity the necessary conditions guaranteeing the global extendibility of singular spacetimes were given. IV. Neutron star models with physically reasonable equation of state were constructed. V. Spherically symmetric stars in models of the universe with non-zero cosmological constant were investigated. VI.The radial stability of neutron star models and the dynamics of matter distribution concentrated on spherical shells were determined. VII. A generic framework of deformed stationary black hole spacetimes was established. VIII. We joined to the Virgo scientific collaboration.The CBwaves software was developed and it was integrated it into various data analyzing algorithms of the LIGO-Virgo collaboration. In relation with the listed achievements 14 theoretical, and 23 experimental papers have been published in high impact scientific journals

Upper Limits on the Rates of Binary Neutron Star and Neutron Star-Black Hole Mergers from Advanced Ligo's First Observing Run

We report here the non-detection of gravitational waves from the merger of binary neutron star systems and neutron-star–black-hole systems during the first observing run of Advanced LIGO. In particular we searched for gravitational wave signals from binary neutron star systems with component masses ∈ [1, 3]M and component dimensionless spins < 0.05. We also searched for neutron-star–black-hole systems with the same neutron star parameters, black hole mass ∈ [2, 99]M and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems, and find that they could have detected the merger of binary neutron star systems with component mass distributions of 1.35±0.13M at a volume-weighted average distance of ∼ 70 Mpc, and for neutron-star–black-hole systems with neutron star masses of 1.4M and black hole masses of at least 5M , a volume-weighted average distance of at least ∼ 110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc−3 yr−1 for binary-neutron star systems and less than 3,600 Gpc−3 yr−1 for neutron-star–black-hole systems. We discuss the astrophysical implications of these results, which we find to be in tension with only the most optimistic predictions. However, we find that if no detection of neutron-star binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates