arXiv subjects

Mark Hannam

Publications and source records attributed to Mark Hannam.

81 records · Page 5Linked to original sources

arXiv2007

Reducing phase error in long numerical binary black hole evolutions with sixth order finite differencing

We describe a modification of a fourth-order accurate ``moving puncture'' evolution code, where by replacing spatial fourth-order accurate differencing operators in the bulk of the grid by a specific choice of sixth-order accurate stencils we gain significant improvements in accuracy. We illustrate the performance of the modified algorithm with an equal-mass simulation covering nine orbits.

gr-qc↗

arXiv2007

Binary black holes on a budget: Simulations using workstations

Binary black hole simulations have traditionally been computationally very expensive: current simulations are performed in supercomputers involving dozens if not hundreds of processors, thus systematic studies of the parameter space of binary black hole encounters still seem prohibitive with current technology. Here we show how the multi-layered refinement level code BAM can be used on dual processor workstations to simulate certain binary black hole systems. BAM, based on the moving punctures method, provides grid structures composed of boxes of increasing resolution near the center of the grid. In the case of binaries, the highest resolution boxes are placed around each black hole and they track them in their orbits until the final merger when a single set of levels surrounds the black hole remnant. This is particularly useful when simulating spinning black holes since the gravitational fields gradients are larger. We present simulations of binaries with equal mass black holes with spins parallel to the binary axis and intrinsic magnitude of S/m^2= 0.75. Our results compare favorably to those of previous simulations of this particular system. We show that the moving punctures method produces stable simulations at maximum spatial resolutions up to M/160 and for durations of up to the equivalent of 20 orbital periods.

gr-qc↗

arXiv2007

Head-On collisions of different initial data

We discuss possible origins for discrepancies observed in the radiated energies in head-on collisions of non-spinning binaries starting from Brill-Lindquist and superposed Kerr-Schild data. For this purpose, we discuss the impact of different choices of gauge parameters and a small initial boost of the black holes.

gr-qc↗

arXiv2007

Total recoil: the maximum kick from nonspinning black-hole binary inspiral

When unequal-mass black holes merge, the final black hole receives a ``kick'' due to the asymmetric loss of linear momentum in the gravitational radiation emitted during the merger. The magnitude of this kick has important astrophysical consequences. Recent breakthroughs in numerical relativity allow us to perform the largest parameter study undertaken to date in numerical simulations of binary black hole inspirals. We study non-spinning black-hole binaries with mass ratios from $q=M_1/M_2=1$ to $q =0.25$ ($η= q/(1 + q)^2$ from 0.25 to 0.16). We accurately calculate the velocity of the kick to within 6%, and the final spin of the black holes to within 2%. A maximum kick of $175.2\pm11$ km s$^{-1}$ is achieved for $η= 0.195 \pm 0.005$.

gr-qc↗

arXiv2007

Where do moving punctures go?

Currently the most popular method to evolve black-hole binaries is the ``moving puncture'' method. It has recently been shown that when puncture initial data for a Schwarzschild black hole are evolved using this method, the numerical slices quickly lose contact with the second asymptotically flat end, and end instead on a cylinder of finite Schwarzschild coordinate radius. These slices are stationary, meaning that their geometry does not evolve further. We will describe these results in the context of maximal slices, and present time-independent puncture-like data for the Schwarzschild spacetime.

gr-qc↗

arXiv2006

Beyond the Bowen-York extrinsic curvature for spinning black holes

It is well-known that Bowen-York initial data contain spurious radiation. Although this ``junk'' radiation has been seen to be small for non-spinning black-hole binaries in circular orbit, its magnitude increases when the black holes are given spin. It is possible to reduce the spurious radiation by applying the puncture approach to multiple Kerr black holes, as we demonstrate for examples of head-on collisions of equal-mass black-hole binaries.

gr-qc↗

arXiv2006

Calibration of Moving Puncture Simulations

We present single and binary black hole simulations that follow the moving puncture paradigm of simulating black-hole spacetimes without excision, and use moving boxes mesh refinement. Focussing on binary black hole configurations where the simulations cover roughly two orbits, we address five major issues determining the quality of our results: numerical discretization error, finite extraction radius of the radiation signal, physical appropriateness of initial data, gauge choice and computational performance. We also compare results we have obtained with the BAM code described here with the independent LEAN code.

gr-qc↗

arXiv2006

Relativistic three-body effects in black hole coalescence

Three-body interactions are expected to be common in globular clusters and in galactic cores hosting supermassive black holes. Here we consider an equal-mass binary-black-hole system in the presence of a third black hole. Using numerically generated binary-black-hole initial-data sets, and first- and second-order post-Newtonian (1PN and 2PN) techniques, we find that the presence of the third black hole has non-negligible relativistic effects on the location of the innermost stable circular orbit (ISCO), and that these effects arise at 2PN order. In particular, we study the more astrophysically realistic situation of a stellar-mass black-hole binary in orbit about a third supermassive black hole. In general, the proximity of the massive black hole has stabilizing effects on the orbiting binary, leading to an increase in merger time and a decrease of the terminal orbital frequency, and an amplification of the gravitational radiation emitted from the binary system by up to 6 percent.

astro-ph↗

arXiv1998

Observable frequency shifts via spin-rotation coupling

The phase perturbation arising from spin-rotation coupling is developed as a natural extension of the celebrated Sagnac effect. Experimental evidence in support of this phase shift, however, has yet to be realized due to the exceptional sensitivity required. We draw attention to the relevance of a series of experiments establishing that circularly polarized light, upon passing through a rotating half-wave plate, is changed in frequency by twice the rotation rate. These experiments may be interpreted as demonstrating the role of spin-rotation coupling in inducing this frequency shift, thus providing direct empirical verification of the coupling of the photon helicity to rotation. A neutron interferometry experiment is proposed which would be sensitive to an analogous frequency shift for fermions. In this arrangement, polarized neutrons enter an interferometer containing two spin flippers, one of which is rotating while the other is held stationary. An observable beating in the transmitted neutron beam intensity is predicted.

gr-qc↗