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Gravitational waves leave behind a recognizable trace, say physicists



  Gravitational Waves "title =" A visualization of a supercomputer simulation of the merging of black holes emitting gravitational waves. Credit: NASA / C. Henze "/>

 
<figcaption class= A visualization of a supercomputer simulation for merging black holes emitting gravitational waves. Credit: NASA / C. Henze

Gravity waves, first discovered in 201

6, provide a new window to the universe with the potential to tell us everything from post-Big Bang to more recent events in galaxy centers.

And while the billion-dollar laser interferometer-gravitational-wave observatory (LIGO detector) monitors around the clock whether gravitational waves are streaming through the earth, new research shows that these waves leave many "memories" that even help to recognize them after they have passed.

"That gravitational waves can leave permanent changes to a detector after passing through the gravitational waves is one of the more unusual predictions of general relativity," said graduate student Alexander Grant, lead author of "Persistent Gravitational" Wave Observables: General Framework, published on the 26th April Physical Review D .

Physicists have long known that gravitational waves leave a memory on their particles, and have identified five such memories. Researchers have now discovered three more after effects of passing a gravitational wave, "persistent gravitational wave observables," which one day could help determine waves that travel through the universe.

Every new observable, says Grant, offers several possibilities to validate the theory of General Theory of Relativity and provides insight into the intrinsic properties of gravitational waves.

These properties, the researchers say, could help extract information from the cosmic microwave background – the radiation left over from the Big Bang.

"We did not anticipate the richness and diversity of what could be observed," said Éanna Flanagan, Edward L. Nichols Professor and Chair of Physics and Professor of Astronomy.




This computer simulation shows the collision of two black holes, a hugely powerful event for the first time with the Laser Interferometer Gravitational Wave Observatory, which detected gravitational waves as a spiral of black holes, colliding and merging. This simulation shows what the fusion event would look like if humanity could travel closer. It was created by Cornell's SXS (Simulating eXtreme Spacetimes) project. Credit: Cornell University

"What came as a surprise to me in this research is how different ideas were sometimes unexpectedly associated," Grant said. "We looked at a variety of observables and found that in order to know something about one, one had to understand the other."

The researchers identified three observables that show the effects of gravitational waves in a flat region in space-time, which experiences a barrage of gravitational waves, and then back to a flat region. The first observable "curve divergence" is how far two accelerating observers separate from one another as compared to how observers with the same accelerations in a shallow space would separate undisturbed from a gravitational wave.

"Holonomy" is obtained by transporting information about the linear momentum and angular momentum of a particle along two different curves through the gravitational waves and comparing the two different results.

The third section examines how gravitational waves affect the relative displacement of two particles when one of the particles has an intrinsic spin.

Each of these observables is defined by the researchers in a way that could be measured by a detector. The detection methods for the curve deviation and the rotating particles are "relatively straightforward", the researchers write and only demand "a means for measuring the separation and the observation of the respective accelerations".

Detecting observable holonomy It would be more difficult, she wrote, "to require two observers to measure the local curvature of spacetime (possibly by carrying small gravitational wave detectors themselves)." Given the size LIGO needs to detect just one gravitational wave, the ability to capture observable holonomic observables is beyond the reach of contemporary science, researchers say.

"But we've seen a lot of exciting things with gravitational waves, and we'll see a lot more, and there are even plans to place a gravitational wave detector in space that would be sensitive to sources other than LIGO," Flanagan said.


Researchers discover new properties of the gravitational wave


Further information:
Éanna É. Flanagan et al., Persistent Gravitational Waves Observables: General Framework, Physical Review D (2019). DOI: 10.1103 / PhysRevD.99.084044

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Gravitational waves leave a recognizable track, say physicists (2019, 9 May)
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