LIGO detects another gravitational wave event

[Stu]

3 hours ago, SilverAstro said:

Hmm, I did not mean to start a debate on the rights or wrongs of the standard model nor conspiracies nor alternative theories, I was just musing on fings wot bovered me ! I know about statistical samples of a few and chi !

Two are supposed to be (have been)  at about 1.4 and 1.5 bly and the other at 3 , so, given that there is 13by to choose from that is the start (maybe)of a clustering (but not a 5sigma I grant !)

Nor was I thinking of the relative numbers of BH there may or may not have been, primordial or otherwise, nor even binary nor even drifted into binorism !

But addressing the analogy of SNs and their early detection (Mk1 eyeball) it seems to me that was dependent upon the inverse sq. law ? Bright = close ??

Supposing that LIGO is the Mk I eyeball of the nouveaux regime  and assuming that the inverse sq. 'brightness' still applies then --- why they all (so far) far away* ? [is there a model that says that about 1 to 3 bly years ago there was a special time for bright bh mergers, or is it a statistical fluctuation in a broad spectrum of events]

I find on the interweb much discussion on the expected (supposed, depending which model is chosen) frequency of detection ( varying between several every few seconds to a few every few months) but nothing on the frequency over time / distance / age of the universe ? * ?

 

Some great questions there; I suspect most of the answers are not yet fully known so it will be fascinating to see how this unfolds as more detections occur.

[The Admiral]

Indeed, you have raised some interesting questions SA. I've not had the benefit of searching the interweb for some answers, but it strikes me that our detections so far have really only been of a small sub-set of possible gravity wave sources, and I wouldn't be sure of any inferences. Still, that doesn't stop scientists postulating various scenarios (it's the nature of scientific investigation after all). I agree that on the face of it one might infer that there was a special time in the history of the universe when conditions were favourable. I've come to the point where adding yet another bizarre situation to an already befuddling history ceases to surprise me!

Ian

[andrew s]

5 hours ago, SilverAstro said:

Supposing that LIGO is the Mk I eyeball of the nouveaux regime  and assuming that the inverse sq. 'brightness' still applies then --- why they all (so far) far away* ? [is there a model that says that about 1 to 3 bly years ago there was a special time for bright bh mergers, or is it a statistical fluctuation in a broad spectrum of events]

While the inverse sq. law dims gravitational waves it has the reverse effect on the volume of space. So if BH are uniformly distributed (on large scales)  then their number goes up as the square of the distance from us. You could then speculate that at 1 to 3 bly years the trade-off between number and brightness is optimal. However, this would need to be put it to the test as more observations are made as the current sample is too small on which to base such a view.

I am not aware of any model that says 1 to 3 bly was a special time for bright BH mergers. 

Regards Andrew

PS You may be interested in this debate https://www.physicsforums.com/threads/ligo-was-it-all-just-noise.917785/page-2#post-5789550

[SilverAstro]

1 hour ago, andrew s said:

 not aware of any model that says 1 to 3 bly was a special time

Thanks, that makes two of us now ! So we must sit back and await further obs   ( but lack of obs doesnt usually stop the theoreticians modeling/speculating.)

Actually, I have not seen any models postulating any distribution over distance at all   but in my touring of the interweb I did turn up an interesting sideshoot on mini black holes - not being in danger of collapsing the false vacuum (on the grounds that if they could have they would have done so already ! ) but that is a topic for elsewhere

 

[SilverAstro]

2 hours ago, andrew s said:

PS You may be interested in this debate https://www.physicsforums.com/threads/ligo-was-it-all-just-noise.917785/page-2#post-5789550

Thanks, did you mean that particular post or the whole topic ? ( all 3 pages of it !!) I think it was a non-starter from the beginning - quote "what if there wasn't a signal at all, but rather patterns and correlations in the noise" /quote,,  I thought that the LIGO team had already taken great precautions agin that and in fact I would have been surprised if they had not ! Seemed an ok set of detections to me anyway and no doubt the LIGO team will be pleased to have my blessing  lol

[andrew s]

1 minute ago, SilverAstro said:

Thanks, did you mean that particular post or the whole topic ?

The whole topic not a particular post. I should have been more careful with the reference. 

It just shows science at work and the need for a third, independent, detector in my view. I am happy that they have detected Gravitational Waves but while they are the only ones making the detection the critical step of verifying their results remains open.

Regards Andrew

[SilverAstro]

4 minutes ago, andrew s said:

It just shows science at work

and the need for a third

Indeed it does, but sometimes a bit like stirring treacle (threads and topics I mean !!)

indeed seconded if only to better locate events on the celestial sphere. The LIGO team et al would dearly like a third as well.

[The Admiral]

I'm trying to think this through and I'm feeling my brain's not big enough! This is what I understand to be the facts. If the number density of black holes is uniform throughout the universe, then we might assume that the rate of potentially observable mergers should be dominated by those far away. However, if the inverse square law applies to gravity waves then the detection threshold of LIGO will require the mergers from farther away to be between larger masses than those close by, assuming that the wave amplitude increases with merging masses. But, as the masses of the merging BHs increases, so will the wavelength of the waves shorten. As LIGO has a limited bandwidth, then perhaps these events will not be detected. At the other end of the scale, BHs close to us should be detectable given the right masses in terms of bandwidth, but will be fewer in number. Perhaps as Andrew says, may be the 1 - 3 bly represents the peak in observable events.

Another issue that comes to mind is that for black holes to merge then they must at some point get close enough together. A recent report (https://www.sciencealert.com/orbiting-supermassive-black-holes-have-been-observed-for-the-first-time) of the discovery of two super-massive black holes (billions of times the solar mass) resulting from a merger of galaxies makes me wonder if this is how most large BH mergers start out. I wonder whether there was a time in our universe's history when such events were at their maximum likelihood. Which I think could explain AS's concern.

Anyway, I don't know whether that's helped at all (it may be complete .....!), but my 2 cents worth

Ian

[George Jones]

On 2017-06-30 at 04:12, The Admiral said:

if the inverse square law applies to gravity waves then the detection threshold of LIGO

 

The LIGO detectors respond to amplitude, not intensity. This means that the sensitivity the detectors falls as 1/r, not 1/r^2. I have attached an interesting (but somewhat technical) discussion of this.

GW Detection.pdf

[The Admiral]

2 hours ago, George Jones said:

 

The LIGO detectors respond to amplitude, not intensity. This means that the sensitivity the detectors falls as 1/r, not 1/r^2. I have attached an interesting (but somewhat technical) discussion of this.

GW Detection.pdf

That's interesting, George. Thanks for the link. So, if I've got this right, there will be a bias towards more distant events as the number of potentially observable events will go in proportion to distance?

Ian

[Tiki]

On ‎02‎/‎07‎/‎2017 at 11:34, George Jones said:

 

The LIGO detectors respond to amplitude, not intensity. This means that the sensitivity the detectors falls as 1/r, not 1/r^2. I have attached an interesting (but somewhat technical) discussion of this.

GW Detection.pdf

 

Thanks for pointing this out, I'd never really thought this through before and had just assumed that it was the intensity that mattered. It makes me feel good to know that as our gravitational wave detectors improve, then the volume of Universe where we may directly detect 'gravitational wave producing events' increases rapidly.

 

On ‎02‎/‎07‎/‎2017 at 13:49, The Admiral said:

 So, if I've got this right, there will be a bias towards more distant events as the number of potentially observable events will go in proportion to distance?

Ian

 

I am not sure of your question regarding bias. For example, if we are able to double the efficiency of our GW detectors then we will be able to detect GW events in a volume 8 (2^3) times as great as we could before. This is a sevenfold increase in volume meaning that newly detected GW events would be approx. 7 times (actually slightly more than 7) more likely to be more distant than previous detections.

 

All detections are good news to me. Only a few years ago I used to wonder if we would ever be able to directy detect any GW's at all, it seems now that such detectable events might even become commonplace. I can't wait.....

[Stub Mandrel]

And I used to think the universe was strong and stable...

[saac]

The book I'm reading at the moment "The Particle At The End of The Universe" has an anecdote re Hertz's new fangled contraption for detecting radio waves. Apparently when asked what his wave detecting device would ultimately be good for he replied "it's of no use whatsoever" ? Since Hertz's discovery we have grown quite adept at manipulating the electromagnetic field and quite fond of our radios, radars, tv, microwaves, cell phones, WiFi ,,,,,,. Linking back to some earlier comments one can only imagine where this new discovery may lead?

 

Jim

[andrew s]

9 minutes ago, saac said:

The book I'm reading at the moment "The Particle At The End of The Universe" has an anecdote re Hertz's new fangled contraption for detecting radio waves. Apparently when asked what his wave detecting device would ultimately be good for he replied "it's of no use whatsoever" ? Since Hertz's discovery we have grown quite adept at manipulating the electromagnetic field and quite fond of our radios, radars, tv, microwaves, cell phones, WiFi ,,,,,,. Linking back to some earlier comments one can only imagine where this new discovery may lead?

 

Jim

While possible, given the relative strength of the em and gravity forces, I don't think a portable gravity wave transmitter / receiver is just round the corner!

In fact if one was in your pocket the rest of you could be bent round the corner. 

Regards Andrew 

[saac]

2 hours ago, andrew s said:

While possible, given the relative strength of the em and gravity forces, I don't think a portable gravity wave transmitter / receiver is just round the corner!

In fact if one was in your pocket the rest of you could be bent round the corner.

Regards Andrew

I suppose it is much easier to cause an electron to shake up and down than it is to shake a black hole or two? Mind you if the Brane beings in Interstellar could communicate across space by manipulating gravity waves then I,m still holding out for my anti gravity boots? While I agree most likely improbable it would be a tantalising thought having detected gravitational waves if we could discern what further physics they exhibit and potentially exploit. For example what information might be carried in a gravitational wave pertaining to its origin and interactions along its journey?

 

Jim

[andrew s]

I hope gravity waves will allow us to see past the cmb to the very early universe. 

Regards Andrew 

[saac]

38 minutes ago, andrew s said:

I hope gravity waves will allow us to see past the cmb to the very early universe.

Regards Andrew

That would indeed be something to hope for. I suppose it may be too fanciful a possibility that gravitational waves may propagate beyond universes if such multi universe exist. Perhaps one for the science fiction writers. In any respect the boldness and execution of the project is inspirational.

 

 

Jim

[Ravenous]

On ‎09‎/‎07‎/‎2017 at 20:30, saac said:

Mind you if the Brane beings in Interstellar could communicate across space by manipulating gravity waves then I,m still holding out for my anti gravity boots

Just a reminder: that was fiction.

[saac]

5 hours ago, Ravenous said:

Just a reminder: that was fiction.

Indeed it was with none other than Kip Thorne as science consultant.? One of my favourite movies of late. Kip describes in his book of the movie the joy he had when the digital arts team presented him with the preview of the representation of Gargantua , the black hole around which the subject's planets are gravitationally bound. He described the moment where, in his words, he was looking at what was probably the most visually correct representation of a black hole. Of course he did have some attachment as the digital creation was constructed using algorithms he had written ?

Jim

[Ravenous]

18 hours ago, saac said:

Indeed it was with none other than Kip Thorne as science consultant.? One of my favourite movies of late. Kip describes in his book of the movie the joy he had when the digital arts team presented him with the preview of the representation of Gargantua , the black hole around which the subject's planets are gravitationally bound.

Yeah, though the time bit is a bit nutty, for many parts of the movie they went to great lengths to get it technically correct.  There's a paper that was written by the software people on the movie along with Thorne.  Quite(!) complicated mathematical detail but an interesting read.

Abstract here:

https://arxiv.org/abs/1502.03808

Full paper (PDF file about 2MB) here:

https://arxiv.org/pdf/1502.03808.pdf