Gravitational waves without general relativity

strainRobert C. Hilborn
This tutorial leads the reader through the details of calculating the properties of gravitational waves from orbiting binaries, such as two orbiting black holes. Using analogies with electromagnetic radiation, the tutorial presents a calculation that produces the same dependence on the masses of the orbiting objects, the orbital frequency, and the mass separation as does the linear version of General Relativity (GR). However, the calculation yields polarization, angular distributions, and overall power results that differ from those of GR. Nevertheless, the calculation produces waveforms that are very similar to the pre-binary-merger portions of the signals observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO-VIRGO) collaboration. The tutorial should be easily understandable by students who have taken a standard upper-level undergraduate course in electromagnetism.

Read more at https://arxiv.org/ftp/arxiv/papers/1710/1710.04635.pdf

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GW151226: Observation of Gravitational Waves from a 22 Solar-mass Binary Black Hole Coalescence

Figure 1. (Adapted from figure 1 of our publication). The gravitational wave event GW151226 as observed by the twin Advanced LIGO instruments: LIGO Hanford (left) and LIGO Livingston (right). The images show the data recorded by the detectors during the last second before merger as the signal varies as a function of time (in seconds) and frequency (in Hertz or the number of wave cycles per second). To be certain that a real gravitational wave has been observed, we compare the data from the detectors against a pre-defined set of models for merging binaries. This allows us to find gravitational wave signals which are buried deep in the noise from the instruments and nearly impossible to find by eye. The animation shows the detector data with and without removing the best-matching model gravitational-wave signal, making it much easier to identify. The signal can be seen sweeping up in frequency as the two black holes spiral together. This signal is much more difficult to spot by eye than the first detection GW150914!

Figure 1. (Adapted from figure 1 of our publication). The gravitational wave event GW151226 as observed by the twin Advanced LIGO instruments: LIGO Hanford (left) and LIGO Livingston (right). The images show the data recorded by the detectors during the last second before merger as the signal varies as a function of time (in seconds) and frequency (in Hertz or the number of wave cycles per second). To be certain that a real gravitational wave has been observed, we compare the data from the detectors against a pre-defined set of models for merging binaries. This allows us to find gravitational wave signals which are buried deep in the noise from the instruments and nearly impossible to find by eye. The animation shows the detector data with and without removing the best-matching model gravitational-wave signal, making it much easier to identify. The signal can be seen sweeping up in frequency as the two black holes spiral together. This signal is much more difficult to spot by eye than the first detection GW150914!

A few months after the first detection of gravitational waves from the black hole merger event GW150914, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has made another observation of gravitational waves from the collision and merger of a pair of black holes. This signal, called GW151226, arrived at the LIGO detectors on 26 December 2015 at 03:38:53 UTC.

The signal, which came from a distance of around 1.4 billion light-years, was an example of a compact binary coalescence, when two extremely dense objects merge. Binary systems like this are one of many sources of gravitational waves for which the LIGO detectors are searching. Gravitational waves are ripples in space-time itself and carry energy away from such a binary system, causing the two objects to spiral towards each other as they orbit. This inspiral brings the objects closer and closer together until they merge. The gravitational waves produced by the binary stretch and squash space-time as they spread out through the universe. It is this stretching and squashing that can be detected by observatories like Advanced LIGO, and used to reveal information about the sources which created the gravitational waves.

GW151226 is the second definitive observation of a merging binary black hole system detected by the LIGO Scientific Collaboration and Virgo Collaboration. Together with GW150914, this event marks the beginning of gravitational-wave astronomy as a revolutionary new means to explore the frontiers of our Universe….

Read more at: http://www.ligo.org/science/Publication-GW151226/index.php#sthash.GM0EB4ib.dpuf>

Relativity Gets Thorough Vetting from LIGO

The gravitational wave signal observed by the LIGO detectors shows no deviation from what general relativity predicts.

Figure 1: The signal from one of the LIGO detectors in Hanford, Washington, is shown with two representations of the best-fit numerical relativity (NR) waveform. The filtered NR waveform illustrates how the raw waveform is perceived by the detector, showing that for GW150914 the instrument was most sensitive to the late-inspiral, merger, and ringdown of the event (data and analysis scripts from Ref.[9]).

The signal from one of the LIGO detectors in Hanford, Washington, is shown with two representations of the best-fit numerical relativity (NR) waveform. The filtered NR waveform illustrates how the raw waveform is perceived by the detector, showing that for GW150914 the instrument was most sensitive to the late-inspiral, merger, and ringdown of the event

Read more at http://physics.aps.org/articles/v9/52

Detecting “Christodoulou memory effect” with LIGO

Detecting gravitational-wave memory with LIGO: implications of GW150914

 Gravitational-wave strain time series using parameters consistent with GW150914

Gravitational-wave strain time series using parameters consistent with GW150914

Paul D. Lasky, Eric Thrane, Yuri Levin, Jonathan Blackman, Yanbei Chen

It may soon be possible for Advanced LIGO to detect hundreds of binary black hole mergers per year. We show how the accumulation of many such measurements will allow for the detection of gravitational-wave memory: a permanent displacement of spacetime that comes from strong-field, general relativistic effects. We estimate that Advanced LIGO operating at design sensitivity may be able to make a signal-to-noise ratio 3(5) detection of memory with 35(90) events with masses and distance similar to GW150914. Given current merger rate estimates (of one such event per 16 days), this could happen in as few as 1.5(4) years of coincident data collection. We highlight the importance of incorporating higher-order gravitational-wave modes for parameter estimation of binary black hole mergers, and describe how our methods can also be used to detect higher-order modes themselves before Advanced LIGO reaches design sensitivity.

Read more at http://arxiv.org/pdf/1605.01415v1.pdf