## Posts Tagged ‘**Gravitational Waves**’

## From Einstein to spacetime

Gravitational wave astronomy involves people from around the world, all with their our own stories. Dr. Corey Gray, Caltech, is a member of the Siksika Nation (Northern Blackfoot tribe of Alberta) and Scottish. He is the lead operator at the Hanford Observatory of the Laser Interferometer Gravitational wave Observatory. In this hour-long public lecture, Dr. Gray presents a behind-the-scenes look at what it’s been like working at a land-based gravitational wave detector since 1998. He will share a “Top 3” list of his favorite detections as well as the experience of a son having the opportunity to recruit his mother to work with him because of language—the language of spacetime and the Blackfoot people.

The LIGO Scientific Collaboration made big news in 2016 by announcing what has been hailed as “the scientific breakthrough of the century:” the first direct detection of gravitational waves. This was a monumental discovery because it proved a prediction made 100 years earlier by Albert Einstein. LIGO has made many more detections over the years. These detections mark the beginning of a completely new field of science: gravitational wave astronomy.

Dr. Corey received his Bachelor of Science degrees in physics and applied mathematics from Humboldt State University in northern California. After graduation, he was hired as a detector operator by the California Institute of Technology to work for the LIGO Hanford Observatory in Washington state. As a member of the LIGO team, Corey’s work has included working with groups to help build the gravitational wave detector and also operating the detector as a member of the operator team.

He also enjoys outreach & science communication. Over the years he has given keynotes, plenary talks, public colloquia, conference panel sessions, and also a TEDx talk. His speaking engagements have taken him from Banff to Orlando, Montreal to Honolulu and many points in between. He especially loves to share the science of Einstein with Indigenous youth and other underrepresented groups.

## Pi from the sky

**A null test of general relativity from a population of gravitational wave observations**

**Carl-Johan Haster**

Our understanding of observed Gravitational Waves (GWs) comes from matching data to known signal models describing General Relativity (GR). These models, expressed in the post-Newtonian formalism, contain the mathematical constant π. Allowing π to vary thus enables a strong, universal and generalisable null test of GR. From a population of 22 GW observations, we make an astrophysical measurement of π=3.115^{+0.048}_{−0.088}, and prefer GR as the correct theory of gravity with a Bayes factor of 321. We find the variable π test robust against simulated beyond-GR effects.

Read more at https://arxiv.org/abs/2005.05472

## Gravitational Waves: A New Astronomy

**Luc Blanchet**

Contemporary astronomy is undergoing a revolution, perhaps even more important than that which took place with the advent of radioastronomy in the 1960s, and then the opening of the sky to observations in the other electromagnetic wavelengths. The gravitational wave detectors of the LIGO/Virgo collaboration have observed since 2015 the signals emitted during the collision and merger of binary systems of massive black holes at a large astronomical distance. This major discovery opens the way to the new astronomy of gravitational waves, drastically different from the traditional astronomy based on electromagnetic waves. More recently, in 2017, the detection of gravitational waves emitted by the inspiral and merger of a binary system of neutron stars has been followed by electromagnetic signals observed by the γ and X satellites, and by optical telescopes. A harvest of discoveries has been possible thanks to the multi-messenger astronomy, which combines the information from the gravitational wave with that from electromagnetic waves. Another important aspect of the new gravitational astronomy concerns fundamental physics, with the tests of general relativity and alternative theories of gravitation, as well as the standard model of cosmology.

*Read more at https://arxiv.org/pdf/1805.08563.pdf*

## Gravitational waves without general relativity

**Robert 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

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

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>