Magnitude Of Spin Research Articles

Coping with spurious radiation in binary black hole simulations

Spurious junk radiation in the initial data for binary black hole numerical simulations has been an issue of concern. The radiation affects the masses and spins of the black holes, modifying their orbital dynamics and thus potentially compromising the accuracy of templates used in gravitational wave analysis. Our study finds that junk radiation effects are localized to the vicinity of the black holes. Using insights from single black hole simulations, we obtain fitting formulas to estimate the changes from junk radiation on the mass and spin magnitude of the black holes in binary systems. We demonstrate how these fitting formulas could be used to adjust the initial masses and spin magnitudes of the black holes, so the resulting binary has the desired parameters after the junk radiation has left the computational domain. A comparison of waveforms from raw simulations with those from simulations that have been adjusted for junk radiation demonstrate that junk radiation could have an appreciable effect on the templates for LIGO sources with SNRs above 30.

Testing the No-Hair Theorem with GW150914.

We analyze gravitational-wave data from the first LIGO detection of a binary black-hole merger (GW150914) in search of the ringdown of the remnant black hole. Using observations beginning at the peak of the signal, we find evidence of the fundamental quasinormal mode and at least one overtone, both associated with the dominant angular mode (ℓ=m=2), with 3.6σ confidence. A ringdown model including overtones allows us to measure the final mass and spin magnitude of the remnant exclusively from postinspiral data, obtaining an estimate in agreement with the values inferred from the full signal. The mass and spin values we measure from the ringdown agree with those obtained using solely the fundamental mode at a later time, but have smaller uncertainties. Agreement between the postinspiral measurements of mass and spin and those using the full waveform supports the hypothesis that the GW150914 merger produced a Kerr black hole, as predicted by general relativity, and provides a test of the no-hair theorem at the ∼10% level. An independent measurement of the frequency of the first overtone yields agreement with the no-hair hypothesis at the ∼20% level. As the detector sensitivity improves and the detected population of black-hole mergers grows, we can expect that using overtones will provide even stronger tests.

The SXS collaboration catalog of binary black hole simulations

Accurate models of gravitational waves from merging black holes are necessary for detectors to observe as many events as possible while extracting the maximum science. Near the time of merger, the gravitational waves from merging black holes can be computed only using numerical relativity. In this paper, we present a major update of the Simulating eXtreme Spacetimes (SXS) Collaboration catalog of numerical simulations for merging black holes. The catalog contains 2018 distinct configurations (a factor of 11 increase compared to the 2013 SXS catalog), including 1426 spin-precessing configurations, with mass ratios between 1 and 10, and spin magnitudes up to 0.998. The median length of a waveform in the catalog is 39 cycles of the dominant gravitational-wave mode, with the shortest waveform containing 7.0 cycles and the longest 351.3 cycles. We discuss improvements such as correcting for moving centers of mass and extended coverage of the parameter space. We also present a thorough analysis of numerical errors, finding typical truncation errors corresponding to a waveform mismatch of ∼10−4. The simulations provide remnant masses and spins with uncertainties of 0.03% and 0.1% (90th percentile), about an order of magnitude better than analytical models for remnant properties. The full catalog is publicly available at www.black-holes.org/waveforms.

Selective control of surface spin current in topological pyrite-type OsX2 (X\u2009=\u2009Se, Te) crystals

Topological materials host robust surface states that could form the basis for future electronic devices. As such states have spins that are locked to the momentum, they are of particular interest for spintronic applications. Understanding spin textures of the surface states of topologically nontrivial materials, and being able to manipulate their polarization, is therefore essential if they are to be utilized in future technologies. Here we use first-principles calculations to show that pyrite-type crystals OsX2 (X = Se, Te) are a class of topological materials that can host surface states with spin polarization that can be either in-plane or out-of-plane. We show that the formation of low-energy states with symmetry-protected energy- and direction-dependent spin textures on the (001) surface of these materials is a consequence of a transformation from a topologically trivial to nontrivial state, induced by spin orbit interactions. The unconventional spin textures of these surface states feature an in-plane to out-of-plane spin polarization transition in the momentum space protected by local symmetries. Moreover, the surface spin direction and magnitude can be selectively filtered in specific energy ranges. Our demonstration of a new class of topological materials with controllable spin textures provides a platform for experimentalists to detect and exploit unconventional surface spin textures in future spin-based nanoelectronic devices.

Reconstructing phenomenological distributions of compact binaries via gravitational wave observations

Gravitational wave measurements will provide insight into the population of coalescing compact binaries throughout the universe. We describe and demonstrate a flexible parametric method to infer the event rate as a function of compact binary parameters, accounting for Poisson error and selection biases. Using concrete synthetic data based on projections for LIGO and Virgo's O3 run, we discuss how well GW measurements could constrain the mass and spin distribution of coalescing neutron stars and black holes in the near future, within the context of several phenomenological models described in this work. We demonstrate that only a few tens of events can enable astrophysically significant constraints on the spin magnitude and orientation distribution of BHs in merging binaries. We discuss how astrophysical priors or other measurements can inform the interpretation of future measurements. Using publicly-available results, we estimate the event rate versus mass for binary black holes. To connect to previously-published work, we provide estimates including reported O2 BBH candidates, making several unwarranted but simplifying assumptions for the sensitivity of the network and compleness of the reported set of events. Consistent with prior work, we find BHs in binaries likely have low natal spin. With available results and a population favoring low spin, we can't presently constrain the typical misalignments of the binary black hole population. All of the tools described in this work are publicly available and ready-to-use to interpret real or synthetic LIGO data, and to synthesize projected data from future observing runs.

Unraveling the origin of black holes from effective spin measurements with LIGO-Virgo

We investigate how to use information on the effective spin parameter of binary black hole mergers from the LIGO-Virgo gravitational wave detections to discriminate the origin of the merging black holes. We calculate the expected probability distribution function for the effective spin parameter for primordial black holes. Using LIGO-Virgo observations, we then calculate odds ratios for different models for the distribution of black holes' spin magnitude and alignment. We evaluate the posterior probability density for a possible mixture of astrophysical and primordial black holes as emerging from current data, and calculate the number of future merger events needed to discriminate different spin and alignment models at a given level of statistical significance.

Tidal Disruptions of Stars by Binary Black Holes: Modifying the Spin Magnitudes and Directions of LIGO Sources in Dense Stellar Environments

Abstract Binary black holes (BBHs) appear to be widespread and are able to merge through the emission of gravitational waves, as recently illustrated by Laser Interferometer Gravitational-Wave Observatory (LIGO). The spin of the BBHs is one of the parameters that LIGO can infer from the gravitational-wave signal and can be used to constrain their production site. If BBHs are assembled in stellar clusters, they are likely to interact with stars, which could occasionally lead to a tidal disruption event (TDE). When a BBH tidally disrupts a star, it can accrete a significant fraction of the debris, effectively altering the spins of the BHs. Therefore, although dynamically formed BBHs are expected to have random spin orientations, tidal stellar interactions can alter their birth spins both in direction and magnitude. Here we investigate how TDEs by BBHs can affect the properties of the BH members as well as exploring the characteristics of the resulting electromagnetic signatures. We conduct hydrodynamic simulations with a Lagrangian Smoothed Particle Hydrodynamics code of a wide range of representative tidal interactions. We find that both spin magnitude and orientation can be altered and temporarily aligned or anti-aligned through accretion of stellar debris, with a significant dependence on the mass ratio of the disrupted star and the BBH members. These tidal interactions feed material to the BBH at very high accretion rates, with the potential to launch a relativistic jet. The corresponding beamed emission is a beacon to an otherwise quiescent BBH.

Black hole spin axis in numerical relativity

Colliding black holes are systems of profound interest in both gravitational-wave astronomy and in gravitation theory, and a variety of methods have been developed for modeling their dynamics in detail. The features of these dynamics are determined by the masses of the holes and by the magnitudes and axes of their spins. While masses and spin magnitudes can be defined in reasonably unambiguous ways, the spin axis is a concept that, despite great physical importance, is seriously undermined by the coordinate freedom of general relativity. Despite a great wealth of detailed numerical simulations of generic spinning black hole collisions, very little attention has gone into defining or justifying the definitions of the spin axis used in the numerical relativity literature. In this paper, we summarize and contrast the various spin direction measures available in the spec code, including a comparison with a method common in other codes, we explain why these measures have shown qualitatively different nutation features than one would expect from post-Newtonian theory, and we derive and implement new measures that give much better agreement.

Longitudinal Spin Fluctuations and Magnetic Ordering Temperature in Metals: First-Principle Modeling and Phase Space Integration Measure

In magnetically ordered metals the magnitude of the local atomic moment become temperature dependent. To deal with this problem on the ab-initio level one need to employ a specific methodology for calculation of the electronic structure that takes into the account the magnetic disorder effects. In addition one needs to setup a special statistical models allowing simultaneously for ab-initio mapping and for the variation of the local spin magnitude. To this end here we discuss and employ methodology that is based on the Disordered Local Moment (DLM) formalism, spin-constraint Local Spin Density Approximation (LSDA) and Lichtenstein theorem for calculation of the inter-site exchange interactions. An extended classical Heisenberg Hamiltonian used for mapping allows for the variation of the lattice site spin magnitude. We consider here three representative canonical transition metals ferromagnets hcp Gd, bcc Fe and fcc Ni with quite a different character of the magnetic moment localization and illustrate the relative importance of the longitudinal spin fluctuations and the magnetic disorder induced electronic structure reconstruction. We use recently introduced linear measure [1] for integration over the longitudinal spin component in the classical configurational spin space.

Gravitational wave beacons

We explore spinning, precessing, unequal mass binary black holes to display the long term orbital angular momentum, $\vec{L}$, flip dynamics. We study two prototypical cases of binaries with mass ratios $q=1/7$ and $q=1/15$ and a misaligned spin of the large black hole (with an intrinsic spin magnitude of $S_2/m_2^2=0.85$). We conduct full numerical simulations, for nearly 14 and 18 orbits respectively, to evolve the binary down to merger and display a full $L$-flip cycle. The pattern of radiation of such systems is particularly interesting, displaying strong polarization-dependent variation of amplitudes at precessional frequencies, leading to distinctive observational consequences for ground, space, and pulsar timing based gravitational wave detectors. These waveform features are strongly directional dependent and measurements of gravitational waves polarizations can be exploited to disentangle the binary's parameters in various astrophysical scenarios.

Disproving hidden variable models with spin magnitude conservation

The squares of the three components of the spin-s operators sum up to s(s + 1). However, a similar relation is rarely satisfied by the set of possible spin projections onto mutually orthogonal directions. This has fundamental consequences if one tries to construct a hidden variable (HV) theory describing measurements of spin projections. We propose a test of local HV models in which spin magnitudes are conserved. These additional constraints imply that the corresponding inequalities are violated within quantum theory by larger classes of correlations than in the case of standard Bell inequalities. We conclude that in any HV theory pertaining to measurements on a spin one can find situations in which either HV assignments do not represent a physical reality of a spin vector, but rather provide a deterministic algorithm for prediction of the measurement outcomes, or HV assignments represent a physical reality, but the spin cannot be considered as a vector of fixed length.

High-Accuracy Mass, Spin, and Recoil Predictions of Generic Black-Hole Merger Remnants.

We present accurate fits for the remnant properties of generically precessing binary black holes, trained on large banks of numerical-relativity simulations. We use Gaussian process regression to interpolate the remnant mass, spin, and recoil velocity in the seven-dimensional parameter space of precessing black-hole binaries with mass ratios q≤2, and spin magnitudes χ_{1}, χ_{2}≤0.8. For precessing systems, our errors in estimating the remnant mass, spin magnitude, and kick magnitude are lower than those of existing fitting formulae by at least an order of magnitude (improvement is also reported in the extrapolated region at high mass ratios and spins). In addition, we also model the remnant spin and kick directions. Being trained directly on precessing simulations, our fits are free from ambiguities regarding the initial frequency at which precessing quantities are defined. We also construct a model for remnant properties of aligned-spin systems with mass ratios q≤8, and spin magnitudes χ_{1}, χ_{2}≤0.8. As a byproduct, we also provide error estimates for all fitted quantities, which can be consistently incorporated into current and future gravitational-wave parameter-estimation analyses. Our model(s) are made publicly available through a fast and easy-to-use Python module called surfinBH.

Properties of the Binary Neutron Star Merger GW170817

On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal, GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we improve initial estimates of the binary's properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also compare results inferred using several signal models, which are more accurate and incorporate additional physical effects as compared to the initial analysis. We improve the localization of the gravitational-wave source to a 90% credible region of $16~\mathrm{deg}^2$. We find tighter constraints on the masses, spins, and tidal parameters, and continue to find no evidence for nonzero component spins. The component masses are inferred to lie between 1.00 and 1.89 $M_\odot$ when allowing for large component spins, and to lie between 1.16 and 1.60 $M_\odot$ (with a total mass $2.73^{+0.04}_{-0.01} \, M_\odot$) when the spins are restricted to be within the range observed in Galactic binary neutron stars. Under minimal assumptions about the nature of the compact objects, our constraints for the tidal deformability parameter $\tilde \Lambda$ are $(0,630)$ when we allow for large component spins, and $300^{+420}_{-230}$ (using a 90% highest posterior density interval) when restricting the magnitude of the component spins, ruling out several equation-of-state models at the 90% credible level. Finally, with LIGO and GEO600 data, we use a Bayesian analysis to place upper limits on the amplitude and spectral energy density of a possible post-merger signal. (Abridged)

Vector-Resolved Magnetooptic Kerr Effect Measurements of Spin–Orbit Torque

We demonstrate simultaneous detection of current-driven dampinglike and fieldlike spin–orbit torques in heavy metal/ferromagnetic metal bilayers by measuring all three magnetization components $m_{x},m_{y}$ , and $m_{z} $ using a vector-resolved magnetooptic Kerr effect (MOKE) technique based on quadrant detection. We investigate the magnitude and direction of spin–orbit torques in a series of platinum/permalloy samples, finding good agreement with results obtained via polar and quadratic MOKE measurements without quadrant detection.

Tunable valley and spin splitting in 2H-VSe2/BiFeO3(111) triferroic heterostructures.

The spin and valley degrees of freedom in monolayer transition metal dichalcogenides have potential applications in spintronics and valleytronics. However, nonvolatile control on the valley and spin degrees of freedom of two-dimensional ferromagnetic materials by multiferroic materials has been rarely reported. Here, the electronic structure of monolayer 2H-VSe2/BiFeO3(111) triferroic heterostructures has been investigated by first-principles calculations. It is found that the V magnetic moment, spin and valley splitting of monolayer VSe2 can be affected by the BiFeO3(111) substrate with ferroelectric polarization and G-type antiferromagnetic order. Particularly, the reversed orientation of ferroelectric polarization and magnetic order of the BiFeO3(111) substrate can modulate the magnitude of spin and valley splitting, and change the spin splitting direction and the spin-dependent valley state in the valence band of monolayer VSe2. The coupling among ferroelectrics, magnetism and ferrovalley is realized in 2H-VSe2/BiFeO3(111) triferroic heterostructures. These results provide a new platform for multiferroic regulation in spintronics and valleytronics, which can enrich the diversity for high-performance devices based on two dimensional multiferroic heterostructures.

Constraining Black Hole Spins with Gravitational-wave Observations

Abstract The observation of gravitational-wave signals from merging black hole binaries enables direct measurement of the properties of the black holes. An individual observation allows measurement of the black hole masses, but only limited information about either the magnitude or orientation of the black hole spins is available, primarily due to the degeneracy between measurements of spin and binary mass-ratio. Using the first six black hole merger observations, we are able to constrain the distribution of black hole spins. We perform model selection between a set of models with different spin population models, combined with a power-law mass distribution, to make inferences about the spin distribution. We assume a fixed power-law mass distribution for the black holes, which is supported by the data and provides a realistic distribution of the binary mass-ratio. This allows us to accurately account for selection effects due to variations in the signal amplitude with spin magnitude, and provides an improved inference on the spin distribution. We conclude that the first six LIGO and Virgo observations disfavor highly spinning black holes against low spins by an odds ratio of 15:1, thus providing strong constraints on spin magnitudes from gravitational-wave observations. Furthermore, we are able to rule out a population of binaries with completely aligned spins, even when the spins of the individual black holes are low, at an odds ratio of 22000:1, significantly strengthening earlier evidence against aligned spins. These results provide important information that will aid in our understanding of the formation processes of black holes.

Solution Conformation of Heparin Tetrasaccharide. DFT Analysis of Structure and Spin⁻Spin Coupling Constants.

Density functional theory (DFT) has provided detailed information on the molecular structure and spin–spin coupling constants of heparin tetrasaccharide (GlcNS,6S-IdoA2S-GlcNS,6S-IdoA2S-OMe) representing the predominant heparin repeating-sequence. The fully optimised molecular structures of two tetrasaccharide conformations (differing from each other in the conformational form of the sulphated iduronic acid residue–one 1C4 and the other 2S0) were obtained using the B3LYP/6-311+G(d,p) level of theory and applying explicit water molecules to simulate the presence of a solvent. The theoretical data provided insight into variations of the bond lengths, bond angles and torsion angles, formations of intra- and intermolecular hydrogen bonds and ionic interactions. Optimised molecular structures indicated the formation of a complex hydrogen bond network, including interresidue and intraresidue bonds. The ionic interactions strongly influence the first hydration shell and, together with hydrogen bonds, play an important role in shaping the 3D tetrasaccharide structure. DFT-derived indirect three–bond proton–proton coupling constants (3JH-C-C-H) showed that the best agreement with experiment was obtained with a weighted average of 67:33 (1C4:2S0) of the IdoA2S forms. Detailed analysis of Fermi-contact contributions to 3JH-C-C-H showed that important contributions arise from the oxygen lone pairs of neighbouring oxygen atoms. The analysis also showed that the magnitude of diamagnetic spin–orbit contributions are sufficiently large to determine the magnitude of some proton–proton coupling constants. The data highlight the need to use appropriate quantum-chemical calculations for a detailed understanding of the solution properties of heparin oligosaccharides.

Tunable Spin-Superconductor Coupling of Spin 1/2 Vanadyl Phthalocyanine Molecules.

Atomic-scale magnetic moments in contact with superconductors host rich physics based on the emergence of Yu-Shiba-Rusinov (YSR) magnetic bound states within the superconducting condensate. Here, we focus on a magnetic bound state induced into Pb nanoislands by individual vanadyl phthalocyanine (VOPc) molecules deposited on the Pb surface. The VOPc molecule is characterized by a spin magnitude of 1/2 arising from a well-isolated singly occupied d xy-orbital and is a promising candidate for a molecular spin qubit with long coherence times. X-ray magnetic circular dichroism (XMCD) measurements show that the molecular spin remains unperturbed even for molecules directly deposited on the Pb surface. Scanning tunneling spectroscopy and density functional theory (DFT) calculations identify two adsorption geometries for this "asymmetric" molecule (i.e., absence of a horizontal symmetry plane): (a) oxygen pointing toward the vacuum with the Pc laying on the Pb, showing negligible spin-superconductor interaction, and (b) oxygen pointing toward the Pb, presenting an efficient interaction with the Pb and promoting a Yu-Shiba-Rusinov bound state. Additionally, we find that in the first case a YSR state can be induced smoothly by exerting mechanical force on the molecules with the scanning tunneling microscope (STM) tip. This allows the interaction strength to be tuned continuously from an isolated molecular spin case, through the quantum critical point (where the bound state energy is zero) and beyond. DFT indicates that a gradual bending of the VO bond relative to the Pc ligand plane promoted by the STM tip can modify the interaction in a continuously tunable manner. The ability to induce a tunable YSR state in the superconductor suggests the possibility of introducing coupled spins on superconductors with switchable interaction.

Visualizing Intramolecular Distortions as the Origin of Transverse Magnetic Anisotropy.

The magnetic properties of metal-organic complexes are strongly influenced by conformational changes in the ligand. The flexibility of Fe-tetra-pyridyl-porphyrin molecules leads to different adsorption configurations on a Au(111) surface. By combining low-temperature scanning tunneling spectroscopy and atomic force microscopy, we resolve a correlation of the molecular configuration with different spin states and magnitudes of magnetic anisotropy. When the macrocycle exhibits a laterally undistorted saddle shape, the molecules lie in a S = 1 state with axial anisotropy arising from a square-planar ligand field. If the symmetry in the molecular ligand field is reduced by a lateral distortion of the molecule, we find a finite contribution of transverse anisotropy. Some of the distorted molecules lie in a S = 2 state, again exhibiting substantial transverse anisotropy.

Spin orientations of merging black holes formed from the evolution of stellar binaries

We study the expected spin misalignments of merging binary black holes (BHs) formed in isolation by combining state-of-the-art population-synthesis models with efficient post-Newtonian evolutions, thus tracking sources from stellar formation to gravitational-wave detection. We present extensive predictions of the properties of sources detectable by both current and future interferometers. We account for the fact that detectors are more sensitive to spinning BH binaries with suitable spin orientations and find that this significantly impacts the population of sources detectable by LIGO, while this is not the case for 3rd-generation detectors. We find that three formation pathways, differentiated by the order of core collapse and common-envelope phases, dominate the observed population, and that their relative importance critically depends on the recoils imparted to BHs at birth. Our models suggest that measurements of the "effective-spin" parameter $\chi_{\rm eff}$ will allow for powerful constraints. For instance, we find that the role of spin magnitudes and spin directions in $\chi_{\rm eff}$ can be largely disentangled, and that the symmetry of the effective-spin distribution is a robust indicator of the binary's formation history. Our predictions for individual spin directions and their precessional morphologies confirm and extend early toy models, while exploring substantially more realistic and broader sets of initial conditions. Our main conclusion is that specific subpopulations of BH binaries will exhibit distinctive precessional dynamics: these classes include (but are not limited to) sources where stellar tidal interactions act on sufficiently short timescales, and massive binaries produced in pulsational pair-instability supernovae. Measurements of BH spin orientations have enormous potential to constrain specific evolutionary processes in the lives of massive binary stars.