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44 comments### Binare zahlen in hexadezimal umrechnen

Search SciRate Search query. Gravitational wave spectroscopy of binary neutron star merger remnants with mode stacking. As in the case of binary black holes, GWs generated by BNS consist of inspiral, merger, and post-merger components. Detecting the latter is important because it encodes information about the nuclear equation of state EOS in a regime that cannot be probed prior to merger.

We carry out Monte-Carlo simulations showing that the dominant post-merger signal the 22 mode from individual events will likely not be observable even with the Einstein Telescope and Cosmic Explorer CE , assuming a full year of operation, the latest merger rates, and a detection threshold with signal-to-noise ratio of 5.

For this reason, we propose two methods that stack the post-merger signal from multiple events to boost the detection probability. The first method follows a commonly-used practice of multiplying the Bayes factors of individual events. The second method relies on an assumption that the mode phase can be determined from the inspiral waveform, so that coherent mode stacking of the data from different events becomes possible.

Both methods significantly improve the chances of detecting the dominant post-merger signal, making a detection very likely after a year of observation with CE for certain EOS. We also show that in terms of detection, coherent stacking is more efficient in accumulating confidence. Apr 18 gr-qc astro-ph. We study the growth and saturation of the superradiant instability of a complex, massive vector Proca field as it extracts energy and angular momentum from a spinning black hole, using numerical solutions of the full Einstein-Proca equations.

In all cases studied, the superradiant instability smoothly saturates when the black hole's horizon frequency decreases to match the frequency of the Proca cloud that spontaneously forms around the black hole.

Black hole spectroscopy with coherent mode stacking. The measurement of multiple ringdown modes in gravitational waves from binary black hole mergers will allow for testing fundamental properties of black holes in General Relativity, and to constrain modified theories of gravity. We first rescale each signal so that the target mode in each of them has the same frequency, and then sum the waveforms constructively.

A crucial element to realize this coherent superposition is to make use of a priori information extracted from the inspiral-merger phase of each event.

We show that this method can significantly boost the signal-to-noise ratio of the collective target mode compared to that of the single loudest event. Using current estimates of merger rates we show that it is likely that advanced-era detectors can measure this collective ringdown mode with one year of coincident data gathered at design sensitivity. Equation of state effects and one-arm spiral instability in hypermassive neutron stars formed in eccentric neutron star mergers. East, Vasileios Paschalidis, Frans Pretorius.

Sep 06 astro-ph. We continue our investigations of the development and importance of the one-arm spiral instability in long-lived hypermassive neutron stars HMNSs formed in dynamical capture binary neutron star mergers. Employing hydrodynamic simulations in full general relativity, we find that the one-arm instability is generic in that it can develop in HMNSs within a few tens of milliseconds after merger for all equations of state in our survey.

Thus, if gravitational waves from the one-arm instability are detected, they could in principle constrain the neutron star equation of state. Finally, we provide estimates of the properties of dynamical ejecta, as well as the accompanying kilonovae signatures. Mar 31 gr-qc astro-ph. HE hep-ph hep-th arXiv: The gravitational wave observations GW and GW by Advanced LIGO provide the first opportunity to learn about physics in the extreme gravity environment of coalescing binary black holes.

This paper expands their analysis to a larger class of anomalies, highlighting the inferences that can be drawn on non-standard theoretical physics mechanisms. We find that these events constrain a plethora of mechanisms associated with the generation and propagation of gravitational waves, including the activation of scalar fields, gravitational leakage into large extra dimensions, the variability of Newton's constant, a modified dispersion relation, gravitational Lorentz violation and the strong equivalence principle.

Though other observations limit many of these mechanisms already, GW and GW are unique in that they are direct probes of dynamical strong-field gravity and of gravitational wave propagation. We also show that GW constrains inferred properties of exotic compact object alternatives to Kerr black holes. We argue, however, that the true potential for GW to both rule out exotic objects and constrain physics beyond General Relativity is severely limited by the lack of understanding of the merger regime in almost all relevant modified gravity theories.

This event thus significantly raises the bar that these theories have to pass, both in terms of having a sound theoretical underpinning, and being able to solve the equations of motion for binary merger events. We conclude with a discussion of the additional inferences that can be drawn if the lower-confidence observation of an electromagnetic counterpart to GW holds true; this would provide dramatic constraints on the speed of gravity and gravitational Lorentz violation.

Spontaneous Scalarization with Massive Fields. We study the effect of a mass term in the spontaneous scalarization of neutron stars, for a wide range of scalar field parameters and neutron star equations of state. Even though massless scalars have been the focus of interest in spontaneous scalarization so far, recent observations of binary systems rule out most of their interesting parameter space.

We point out that adding a mass term to the scalar field potential is a natural extension to the model that avoids these observational bounds if the Compton wavelength of the scalar is small compared to the binary separation. Our model is formally similar to the asymmetron scenario recently introduced in application to cosmology, though here we are interested in consequences for neutron stars and thus consider a mass term that does not modify the geometry on cosmological scales.

We review the allowed values for the mass and scalarization parameters in the theory given current binary system observations and black hole spin measurements. We show that within the allowed ranges, spontaneous scalarization can have nonperturbative, strong effects that may lead to observable signatures in binary neutron star or black hole-neutron star mergers, or even in isolated neutron stars.

Gravity-dominated unequal-mass black hole collisions. Nov 30 gr-qc hep-ph hep-th arXiv: We continue our series of studies of high-energy collisions of black holes investigating unequal-mass, boosted head-on collisions in four dimensions.

We support this conclusion with calculations using black hole perturbation theory and Smarr's zero-frequency limit approximation. These results lend strong support to the conjecture that the detailed structure of the colliding objects is irrelevant at high energies.

Nov 05 astro-ph. We perform general-relativistic hydrodynamical simulations of dynamical capture binary neutron star mergers, emphasizing the role played by the neutron star spin. Dynamical capture mergers may take place in globular clusters, as well as other dense stellar systems, where most neutron stars have large spins.

We find significant variability in the merger outcome as a function of initial neutron star spin. For cases where the spin is aligned with the orbital angular momentum, the additional centrifugal support in the remnant hypermassive neutron star can prevent the prompt collapse to a black hole, while for antialigned cases the decreased total angular momentum can facilitate the collapse to a black hole.

We show that even moderate spins can significantly increase the amount of ejected material, including the amount unbound with velocities greater than half the speed of light, leading to brighter electromagnetic signatures associated with kilonovae and interaction of the ejecta with the interstellar medium.

Furthermore, we find that the initial neutron star spin can strongly affect the already rich phenomenology in the postmerger gravitational wave signatures that arise from the oscillation modes of the hypermassive neutron star. For long-lived hypermassive neutron stars, the presence of this instability leads to improved prospects for detecting these events through gravitational waves, and thus may give information about the neutron star equation of state.

Vasileios Paschalidis, William E. East, Frans Pretorius, Stuart L. Oct 14 astro-ph. Using general-relativistic hydrodynamical simulations, we show that merging binary neutron stars can form hypermassive neutrons stars that undergo the one-arm spiral instability. We study the particular case of a dynamical capture merger where the stars have a small spin, as may arise in globular clusters, and focus on an equal-mass scenario where the spins are aligned with the orbital angular momentum. We find that this instability develops when post-merger fluid vortices lead to the generation of a toroidal remnant - a configuration whose maximum density occurs in a ring around the center-of-mass - with high vorticity along its rotation axis.

The instability also leaves a characteristic imprint on the post-merger gravitational wave signal that could be detectable if the instability persists in long-lived remnants. Eccentric mergers of black holes with spinning neutron stars. Mar 26 astro-ph. We study dynamical capture binary black hole-neutron star BH-NS mergers focusing on the effects of the neutron star spin. These events may arise in dense stellar regions, such as globular clusters, where the majority of neutron stars are expected to be rapidly rotating.

We initialize the BH-NS systems with positions and velocities corresponding to marginally unbound Newtonian orbits, and evolve them using general-relativistic hydrodynamical simulations.

We find that even moderate spins can significantly increase the amount of mass in unbound material. In some of the more extreme cases, there can be up to a third of a solar mass in unbound matter. Similarly, large amounts of tidally stripped material can remain bound and eventually accrete onto the BHas much as a tenth of a solar mass in some cases.

These simulations demonstrate that it is important to treat neutron star spin in order to make reliable predictions of the gravitational wave and electromagnetic transient signals accompanying these sources.

Choptuik, Luis Lehner, Frans Pretorius. Feb 25 gr-qc astro-ph. This article is an overview of the contributions numerical relativity has made to our understanding of strong field gravity, to be published in the book "General Relativity and Gravitation: A Centennial Perspective", commemorating the th anniversary of general relativity. Numerical Relativity and Astrophysics. Luis Lehner, Frans Pretorius. May 20 astro-ph. Throughout the Universe many powerful events are driven by strong gravitational effects that require general relativity to fully describe them.

Many of these processes trigger emission across a broad range of the electromagnetic spectrum. Compact binaries further source strong gravitational wave emission that could directly be detected in the near future. This feat will open up a gravitational wave window into our Universe and revolutionize its understanding.

Describing these phenomena requires general relativity, and --where dynamical effects strongly modify gravitational fields-- the full Einstein equations coupled to matter sources.

Numerical relativity is a field within general relativity concerned with studying such scenarios that cannot be accurately modeled via perturbative or analytical calculations.

In this review, we examine results obtained within this discipline, with a focus on its impact in astrophysics. Apr 02 gr-qc astro-ph. The population of stellar-mass, compact object binaries that merge with non-negligible eccentricity may be large enough to motivate searches with ground-based gravitational wave detectors. Such events could be exceptional laboratories to test General Relativity in the dynamical, strong-field regime, as a larger fraction of the energy is emitted at high-velocities, compared to quasi-circular inspirals.

A serious obstacle here, however, is the challenge of computing theoretical waveforms for eccentric systems with the requisite accuracy for use in a matched-filter search. The corresponding waveforms are more a sequence of concentrated bursts of energy emitted near periapse than a continuous waveform.

Based on this, an alternative approach, stacking excess power over the set of time-frequency tiles coincident with the bursts, was recently suggested as a more practical though sub-optimal detection strategy. The leading-order "observable" that would be inferred from such a detection would be a sequence of discrete numbers characterizing the position and size of each time-frequency tile.

In General Relativity, this possibly large sequence of numbers is uniquely determined by the small set of parameters describing the binary at formation. In this work, following the spirit of the parameterized post-Einsteinian framework developed for quasi-circular inspiral, we propose a simple, parameterized deformation of the baseline general relativistic burst algorithm for eccentric inspiral events that would allow for model-independent tests of Einstein's theory in this high-velocity, strong-field regime.

Detecting gravitational waves from highly eccentric compact binaries. Kai Sheng Tai, Sean T. In dense stellar regions, highly eccentric binaries of black holes and neutron stars can form through various n-body interactions.

Such a binary could emit a significant fraction of its binding energy in a sequence of largely isolated gravitational wave bursts prior to merger.