NANOGrav announces evidence of gravitational wave background

[TheVat]

https://arstechnica.com/science/2023/06/nanograv-picks-up-signal-of-cosmic-choir-of-supermassive-black-holes/

 

Gravitational waves are ripples in the fabric of spacetime predicted by Albert Einstein's general theory of relativity, first detected in 2015. But an expected corresponding low-frequency gravitational wave background—a kind of "hum" comprised of a chorus of gravitational waves, most likely emanating from binary pairs of supermassive black holes—has proven more elusive. Now the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has announced the first evidence of this gravitational wave background. The results and related analyses are described in several new papers published in the The Astrophysical Journal Letters.

(....)

The idea behind NANOGrav is that as gravitational waves stretch and shrink spacetime, this will disrupt the pulsars' ultra-precise "ticking." There should be a telltale signature in the form of a kind of “shimmering” effect, produced because pulses affected by gravitational waves should arrive slightly earlier or later in response to those ripples in spacetime. By studying the timing of the regular signals produced by many individual millisecond pulsars scattered over the sky at the time—called a "pulsar timing array"—NANOGrav tries to detect minute changes in the Earth's position due to the effects of gravitational waves. It just takes many years to do so.

 

[swansont]

One of the things I read is that the pulsars are only measured every few weeks, which works because the GW frequency is so low. That way they can monitor multiple pulsars with their telescope time. Also explains why it took years to get the data, since the period of a 31.5 nHz wave is a year.

[iNow]

On 6/28/2023 at 8:45 PM, TheVat said:

a telltale signature in the form of a kind of “shimmering” effect, produced because pulses affected by gravitational waves should arrive slightly earlier or later in response to those ripples in spacetime.

Perturbations is another word I like in describing this (though shimmering works too)

[StringJunky]

No unperturbed flat spacetime then anywhere?

[iNow]

1 minute ago, StringJunky said:

No unperturbed flat spacetime then anywhere?

Only in yodas mind. Use the force, you must.

[geordief]

4 hours ago, StringJunky said:

No unperturbed flat spacetime then anywhere?

And the gravitational field is being continuously created?

 

If gravitational waves pass through an/the  established gravitational field   is that field changed by the passage of the waves after they have passed through?

Of course the field changes continuously anyway but does the passage of the waves contribute to that change?

 

A pointless question?

[swansont]

3 hours ago, geordief said:

And the gravitational field is being continuously created?

That suggests that they dissipate, which is probably the wrong way to view the classical field

A static field exists. Perturbations/fluctuations happen, which are variations in time.

3 hours ago, geordief said:

 

If gravitational waves pass through an/the  established gravitational field   is that field changed by the passage of the waves after they have passed through?

Of course the field changes continuously anyway but does the passage of the waves contribute to that change?

 

A pointless question?

No change unless the source of the field was somehow changed. Waves obey superposition.

[Genady]

4 hours ago, geordief said:

If gravitational waves pass through an/the  established gravitational field   is that field changed by the passage of the waves after they have passed through?

It is a matter of idealization. This page from Misner, Thorne, Willer explains:

[StringJunky]

Isn't it amazing that this theory just keeps on giving and being confirmed?

[Mordred]

5 hours ago, StringJunky said:

Isn't it amazing that this theory just keeps on giving and being confirmed?

The next several decades with all the equipment proposals to measure the GW wave schotastic should prove interesting. It may likely provide insights beyond the cosmological dark ages including frozen in signals due to inflationary process

[StringJunky]

20 minutes ago, Mordred said:

The next several decades with all the equipment proposals to measure the GW wave schotastic should prove interesting. It may likely provide insights beyond the cosmological dark ages including frozen in signals due to inflationary process

Nice. I probably won't be around then. Would it be like sonar, as an analogy,  measuring the GW Stochastic Background? I just saw this Arxiv paper as I was looking up what you were on about. Have you seen it:

Stochastic gravitational wave background: methods and Implications 

Quote

Beyond individually resolvable gravitational wave events such as binary black hole and binary neutron star mergers, the superposition of many more weak signals coming from a multitude of sources is expected to contribute to an overall background, the so-called stochastic gravitational wave background. In this review, we give an overview of possible detection methods in the search for this background and provide a detailed review of the data-analysis techniques, focusing primarily on current Earth-based interferometric gravitational-wave detectors. In addition, various validation techniques aimed at reinforcing the claim of a detection of such a background are discussed as well. We conclude this review by listing some of the astrophysical and cosmological implications resulting from current upper limits on the stochastic background of gravitational waves.

 

[MigL]

I wonder if we'll ever be able to establish a 'baseline' so that we have a Cosmic Gravitational Background, equivalent to the electromagnetic Cosmic Microwave Background ?

It could tell us a lot about the first instants of our universe, and about gravity itself.

[Mordred]

44 minutes ago, MigL said:

I wonder if we'll ever be able to establish a 'baseline' so that we have a Cosmic Gravitational Background, equivalent to the electromagnetic Cosmic Microwave Background ?

It could tell us a lot about the first instants of our universe, and about gravity itself.

That's the general idea behind the scholastic background. It would give details much like we get with the CMB but closer to the inflationary and electroweak time periods. ( in theory). 

1 hour ago, StringJunky said:

Nice. I probably won't be around then. Would it be like sonar, as an analogy,  measuring the GW Stochastic Background? I just saw this Arxiv paper as I was looking up what you were on about. Have you seen it:

Stochastic gravitational wave background: methods and Implications 

 

Yes I have read that one before it's a pretty decent article. 

[StringJunky]

2 minutes ago, Mordred said:

That's the general idea behind the scholastic background. It would give details much like we get with the CMB but closer to the inflationary and electroweak time periods. ( in theory). 

Yes I have read that one before it's a pretty decent article. 

I thought you might have.