Gravitational waves memories:

[beecee]

https://phys.org/news/2019-05-gravitational-physicists.html

Gravitational waves leave a detectable mark, physicists say: 

extract:

Physicists have long known that gravitational waves leave a memory on the particles along their path, and have identified five such memories. Researchers have now found three more aftereffects of the passing of a gravitational wave, "persistent gravitational wave observables" that could someday help identify waves passing through the universe.

Each new observable, Grant said, provides different ways of confirming the theory of general relativity and offers insight into the intrinsic properties of gravitational waves.

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

the paper:

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.99.084044

Persistent gravitational wave observables: General framework:

ABSTRACT:

The gravitational wave memory effect is characterized by the permanent relative displacement of a pair of initially comoving test particles that is caused by the passage of a burst of gravitational waves. Recent research on this effect has clarified the physical origin and the interpretation of this gravitational phenomenon in terms of conserved charges at null infinity and “soft theorems.” In this paper, we describe a more general class of effects than the gravitational wave memory that are not necessarily associated with these charges and soft theorems, but that are, in principle, measurable. We shall refer to these effects as persistent gravitational wave observables. These observables vanish in nonradiative regions of a spacetime, and their effects “persist” after a region of spacetime which is radiating. We give three examples of such persistent observables, as well as general techniques to calculate them. These examples, for simplicity, restrict the class of nonradiative regions to those which are exactly flat. Our first example is a generalization of geodesic deviation that allows for arbitrary acceleration. The second example is a holonomy observable, which is defined in terms of a closed loop. It contains the usual “displacement” gravitational wave memory; three previously identified, though less well known memory effects (the proper time, velocity, and rotation memories); and additional new observables. Finally, the third example we give is an explicit procedure by which an observer could measure a persistent effect using a spinning test particle. We briefly discuss the ability of gravitational wave detectors (such as LIGO and Virgo) to measure these observables.

[beecee]

https://phys.org/news/2019-05-mathematical-method-black-hole-properties-gravitational-wave.html

A mathematical method for calculating black-hole properties from gravitational-wave data:

Sean McWilliams, an assistant professor at West Virginia University, has developed a mathematical method for calculating black hole properties from gravitational wave data. He has written a paper describing his method and posted it on the arXiv preprint server. The paper has been accepted for publication in Physical Review Letters.

It has been two years since a team working with the LIGO detector made worldwide headlines by announcing that they had detected gravity waves. Since that time, workers there and elsewhere have continued the work, looking to better understand black holes, merging neutron stars, and ultimately, gravity itself. But such work has been hindered in one respect—the source of the gravity waves, merging black holes, is so complicated that it was thought the signals they generate could not be interpreted mathematically. Instead, scientists have been interpreting the signals by comparing them to signals generated using computer simulations.

more at link....

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>

 

the paper:

https://arxiv.org/pdf/1810.00040.pdf

Analytical Black-Hole Binary Merger Waveforms:

We present a highly accurate, fully analytical model for the late inspiral, merger, and ringdown of black-hole binaries with arbitrary mass ratios and spin vectors and the associated gravitational radiation, including the contributions of harmonics beyond the fundamental mode. This model assumes only that nonlinear effects remain small throughout the entire coalescence, and is developed based on a physical understanding of the dynamics of late stage binary evolution, in particular on the tendency of the dynamical binary spacetime to behave like a linear perturbation of the stationary merger-remnant spacetime, even at times before the merger has occurred. We demonstrate that our model agrees with the most accurate numerical relativity results to within their own uncertainties throughout the merger-ringdown phase, and it does so for example cases spanning the full range of binary parameter space that is currently testable with numerical relativity. Furthermore, our model maintains accuracy back to the innermost stable circular orbit of the merger-remnant spacetime over much of the relevant parameter space, greatly decreasing the need to introduce phenomenological degrees of freedom to describe the late inspiral.

[peterwlocke]

same