Another bit of gravity

by Marco De Angelis

After the first detection of gravitational waves from merged black holes, LIGO detected a new signal:

The two LIGO gravitational wave detectors in Hanford Washington and Livingston Louisiana have caught a second robust signal from two black holes in their final orbits and then their coalescence into a single black hole. This event, dubbed GW151226, was seen on December 26th at 03:38:53 (in Universal Coordinated Time, also known as Greenwich Mean Time), near the end of LIGO's first observing period ("O1"), and was immediately nicknamed "the Boxing Day event".

A paper (pdf) about this observation was published on Physical Review Letters:

The inferred component masses are consistent with values dynamically measured in x-ray binaries, but are obtained through the independent measurement process of gravitational-wave detection. Although it is challenging to constrain the spins of the initial black holes, we can conclude that at least one black hole had spin greater than 0.2. These recent detections in Advanced LIGO's first observing period have revealed a population of binary black holes that heralds the opening of the field of gravitational-wave astronomy.

About the first observation, GW150914, you can read Binary Black Hole Mergers in the first Advanced LIGO Observing Run and Dynamical formation of the GW150914 binary black hole (sci-hub) (or Black hole pairs spat out of mosh pits make gravitational waves).

via University of Birmingham

How to produce stationary wave fields

A cylindrical surface of stationary light from
Zamboni-Rached, M., Recami, E., & Hernández-Figueroa, H. (2005). Theory of "frozen waves": modeling the shape of stationary wave fields Journal of the Optical Society of America A, 22 (11) DOI: 10.1364/JOSAA.22.002465 (arXiv)

On the 15th december, 2005, was published an interesting patent (I found it via Research Gate), Method and apparatus for producing stationary intense wave fields of arbitrary shape by Erasmo Recami, Michel Rached Zamboni, Hugo Enrique Ernandez Figueros, Valerio Abate, Cesar Augusto Dartora, Kleber Suza Nobrega, Marco Mattiuzzi:

Method for producing a stationary wave field of arbitrary shape comprising the steps of defining at least one volume being limited in the direction of the axis of propagation of a beam, of the type $0 \leq z \leq L$; defining an intensity pattern within the said region $0 \leq z \leq L$ by a function $F(z)$, describing the said localized and stationary intensity pattern, which is approximated by means of a Fourier expansion or by a similar expansion in terms of (trigonometric) orthogonal functions; providing a generic superposition of Bessel or other beams highly transversally confined; calculating the maximum number of superimposed Bessel beams the amplitudes, the phase velocities and the relative phases of each Bessel beam of the superposition, and the transverse and longitudinal wavenumbers of each Bessel beam of the superposition.

The invention is based on the following theoretical papers: