Author Topic: Gravitational Waves Have Been Detected At LIGO  (Read 89123 times)

Offline RonM

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #280 on: 12/22/2017 04:49 PM »
A new LIGO detector will be built in India by 2025:

http://www.thehindu.com/sci-tech/technology/a-new-ligo-gravitational-wave-detector-to-be-built-in-india-by-2025/article22149855.ece

Curious way that article is written makes it sound like it will be the third detector online, in fact by then it will be the fifth after Italy & Japan.

Thanks though as have been waiting to hear some more information on it.

It will be the third LIGO observatory, not the third gravity wave observatory.

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #281 on: 12/22/2017 04:59 PM »
A new LIGO detector will be built in India by 2025:

http://www.thehindu.com/sci-tech/technology/a-new-ligo-gravitational-wave-detector-to-be-built-in-india-by-2025/article22149855.ece

Curious way that article is written makes it sound like it will be the third detector online, in fact by then it will be the fifth after Italy & Japan.

Thanks though as have been waiting to hear some more information on it.

It will be the third LIGO observatory, not the third gravity wave observatory.

I did wonder if that might be the explanation.

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #282 on: 01/27/2018 08:58 PM »
Details of an upgrade to the Virgo detector.

Quote
A team of researchers from the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover and from the Institute for Gravitational Physics at Leibniz Universität Hannover has developed an advanced squeezed-light source for the gravitational-wave detector Virgo near Pisa. Now, the Hannover scientists have delivered the setup, installed it, and handed it over to their Virgo colleagues. Beginning in autumn 2018 Virgo will use the squeezed-light source to listen to Einstein's gravitational waves together with the worldwide network of detectors with higher sensitivity than ever before.

https://phys.org/news/2018-01-squeezed-light-source-gravitational-detector-sensitive.amp

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #283 on: 01/28/2018 05:48 AM »
Details of an upgrade to the Virgo detector.

Quote
A team of researchers from the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover and from the Institute for Gravitational Physics at Leibniz Universität Hannover has developed an advanced squeezed-light source for the gravitational-wave detector Virgo near Pisa. Now, the Hannover scientists have delivered the setup, installed it, and handed it over to their Virgo colleagues. Beginning in autumn 2018 Virgo will use the squeezed-light source to listen to Einstein's gravitational waves together with the worldwide network of detectors with higher sensitivity than ever before.

https://phys.org/news/2018-01-squeezed-light-source-gravitational-detector-sensitive.amp

Quote
It has increased the part of the Universe that GEO600 listens to by a factor of up to four,
I guess this means that it's increased volume by a factor of four, and hence range by 1.6*, and sensitivity by 2.5* or so.

It would be nice if there was a readily available graph of sensitivity over time for the whole network, including planned updates and estimated occurrance rates of things, but I've not seen anything similar.

Offline jebbo

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #284 on: 01/28/2018 06:42 AM »
The most interesting consequence of this (for me anyway), is that the increased sensitivity means we can probably spot NS-NS mergers up to 15 mins *before* merger, so a better chance of getting more instruments watching earlier. It'll still be tough though, as the sky location still covers a large area.

--- Tony

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #285 on: 01/28/2018 08:50 AM »
Is there some reason that the instrument is given as a loan rather than a permanent addition to Virgo?

Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #286 on: 01/28/2018 09:11 AM »
Is there some reason that the instrument is given as a loan rather than a permanent addition to Virgo?

Well, it's a permanent loan. I guess there are some legal/contractual/funding reasons, which make it necessary that German institutions retain the ownership.

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #287 on: 01/28/2018 09:32 AM »
The most interesting consequence of this (for me anyway), is that the increased sensitivity means we can probably spot NS-NS mergers up to 15 mins *before* merger, so a better chance of getting more instruments watching earlier. It'll still be tough though, as the sky location still covers a large area.
Where are you getting that from?
GW170817 was detected 1.7s before coalescence at 30Hz or so.
Once you get to 10Hz or so, the performance of LIGO is crashing, and is (by eyeballing off the end of a sensitivity graph) 3 orders of magnitude or so worse.
In order for 15 min to be true, with a 2-fold improvement in sensitivity, it would need to be at 20hz for 15 minutes, which seems unlikely.

Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #288 on: 01/28/2018 10:48 AM »
The most interesting consequence of this (for me anyway), is that the increased sensitivity means we can probably spot NS-NS mergers up to 15 mins *before* merger, so a better chance of getting more instruments watching earlier. It'll still be tough though, as the sky location still covers a large area.
Where are you getting that from?
GW170817 was detected 1.7s before coalescence at 30Hz or so.
Once you get to 10Hz or so, the performance of LIGO is crashing, and is (by eyeballing off the end of a sensitivity graph) 3 orders of magnitude or so worse.
In order for 15 min to be true, with a 2-fold improvement in sensitivity, it would need to be at 20hz for 15 minutes, which seems unlikely.

For neutron star inspirals the merger timescale is much longer than for more massive objects with the same orbital period. About 15 minutes in LIGO sensitivity band for NS-NS mergers sounds about right to me. I'll see if I can find a reference...

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #289 on: 01/28/2018 12:04 PM »
For neutron star inspirals the merger timescale is much longer than for more massive objects with the same orbital period. About 15 minutes in LIGO sensitivity band for NS-NS mergers sounds about right to me. I'll see if I can find a reference...

If we neglect frequency and say an equal amount of energy as gravity waves comes out in the last 1.7 seconds and the 15 minutes before that, that is 1/500th the power.
Boosting sensitivity by a factor of 2 can't get you at all close to this, unless the merger is some 16 times closer.


Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #290 on: 01/28/2018 01:23 PM »
For neutron star inspirals the merger timescale is much longer than for more massive objects with the same orbital period. About 15 minutes in LIGO sensitivity band for NS-NS mergers sounds about right to me. I'll see if I can find a reference...

If we neglect frequency and say an equal amount of energy as gravity waves comes out in the last 1.7 seconds and the 15 minutes before that, that is 1/500th the power.
Boosting sensitivity by a factor of 2 can't get you at all close to this, unless the merger is some 16 times closer.

GW170817 was seen for about 100 seconds, so I'm not sure what 1.7 seconds refers to. Anyway, see this Physics Stack Exchange question and especially the second answer about how the chirp mass changes the timescale and amplitude of GW signal.

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #291 on: 01/28/2018 01:55 PM »
For neutron star inspirals the merger timescale is much longer than for more massive objects with the same orbital period. About 15 minutes in LIGO sensitivity band for NS-NS mergers sounds about right to me. I'll see if I can find a reference...

If we neglect frequency and say an equal amount of energy as gravity waves comes out in the last 1.7 seconds and the 15 minutes before that, that is 1/500th the power.
Boosting sensitivity by a factor of 2 can't get you at all close to this, unless the merger is some 16 times closer.

GW170817 was seen for about 100 seconds, so I'm not sure what 1.7 seconds refers to. Anyway, see this Physics Stack Exchange question and especially the second answer about how the chirp mass changes the timescale and amplitude of GW signal.

Apologies, I misread the initial paper - https://arxiv.org/abs/1710.05832 and somehow my eye hit 1.7s (the gamma ray delay) rather than 100s for the time.

100s is the time 'in the detector bandwidth' - the signal only becomes visibly apparent in the graphs presented at -30s or so.

While all of the signal in principle contributes to the detection, if you only consider up to a 'now' point - you will not detect it until it gets to a given threshold - that 100s is not detectable immediately, but maybe only 40 or 15 seconds before the event.

Signals from the three detectors in the above event, from the discovery paper.
« Last Edit: 01/28/2018 02:04 PM by speedevil »

Offline jebbo

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #292 on: 01/28/2018 05:37 PM »
See the reddit they did: https://www.reddit.com/r/IAmA/comments/76yu54/we_are_the_ligo_scientific_collaboration_the/

More specifically, this reply:

Quote
This is an excellent question. The gravitational-wave signal from a binary neutron star such as GW170817 lasts tens of seconds in the most sensitive frequency band of ground-based instruments like LIGO and Virgo. If the signal is sufficiently strong, we can in principle recognize its presence before the merger. We have some seconds of latency due to data transfers between computing centers. Localization also takes some additional seconds. So at the moment this is in practice a bit challenging. Once the detectors reach design sensitivity, however, they will be sensitive to even lower frequencies (starting at about 10 Hz) which effectively increases the duration of the visible signal, possibly even to 15 minutes. Therefore, in the future it should definitely be possible to detect and localize a low-mass binary merger before the actual merger. This is important and exciting as it will allow us to witness the merger with many different observatories.

--- Tony

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #293 on: 01/29/2018 06:22 AM »
See the reddit they did: https://www.reddit.com/r/IAmA/comments/76yu54/we_are_the_ligo_scientific_collaboration_the/

More specifically, this reply:

Quote
This is an excellent question. The gravitational-wave signal from a binary neutron star such as GW170817 lasts tens of seconds in the most sensitive frequency band of ground-based instruments like LIGO and Virgo. If the signal is sufficiently strong, we can in principle recognize its presence before the merger. We have some seconds of latency due to data transfers between computing centers. Localization also takes some additional seconds. So at the moment this is in practice a bit challenging. Once the detectors reach design sensitivity, however, they will be sensitive to even lower frequencies (starting at about 10 Hz) which effectively increases the duration of the visible signal, possibly even to 15 minutes. Therefore, in the future it should definitely be possible to detect and localize a low-mass binary merger before the actual merger. This is important and exciting as it will allow us to witness the merger with many different observatories.

--- Tony

How far away are they to design sensitivity, as it seems like since the first GW detection that they’ve been under constant upgrade?

Offline jebbo

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #294 on: 01/29/2018 07:20 AM »
How far away are they to design sensitivity, as it seems like since the first GW detection that they’ve been under constant upgrade?

Good question. The next observing run (O3) is planned to be a long one (12+ months) running to about the end of 2019. I think they plan on reaching design sensitivity on the next run in ~2020-1, though it isn't clear to me what that next upgrade will bring as I believe the "squeezed light" upgrades are the most significant one and will be done for O3.

Localisation of the sources will be helped when the Japanese instrument, Kagra, joins the network around 2020, which makes any early warning more useful.

So I may have to wait a while longer for us to get as much as 15 minutes warning, but I'm an optimist ;)

Edit: this paper gives more details https://arxiv.org/abs/1304.0670.  Looks like sky localisation will still be problematic until the Indian instrument joins ~2024.

--- Tony
« Last Edit: 01/29/2018 07:26 AM by jebbo »

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #295 on: 01/29/2018 08:33 AM »
How far away are they to design sensitivity, as it seems like since the first GW detection that they’ve been under constant upgrade?

Good question. The next observing run (O3) is planned to be a long one (12+ months) running to about the end of 2019. I think they plan on reaching design sensitivity on the next run in ~2020-1, though it isn't clear to me what that next upgrade will bring as I believe the "squeezed light" upgrades are the most significant one and will be done for O3.

Localisation of the sources will be helped when the Japanese instrument, Kagra, joins the network around 2020, which makes any early warning more useful.

So I may have to wait a while longer for us to get as much as 15 minutes warning, but I'm an optimist ;)

Edit: this paper gives more details https://arxiv.org/abs/1304.0670.  Looks like sky localisation will still be problematic until the Indian instrument joins ~2024.

--- Tony

Thank you.

Is there a more definitive date yet when the Indian LIGO detector will join the network? I’ve previously seen 2024/2025.

Offline Star One

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Gravitational Waves Have Been Detected At LIGO
« Reply #296 on: 11/02/2018 11:05 PM »
In this week’s New Scientist magazine there is a special investigation casting doubt on the 2015 discovery of gravitational waves. I don’t have all the details as I only received my copy today and haven’t had a chance to read the article properly yet but it appears to be based on the work of a gentleman called Andrew Jackson who is the spokesman for a group based at the Niels Bohr Institute in Copenhagen. The basics of the article after skimming it are that the LIGO group are too secretive with their data when it comes to independent verification, that we have to rely on effectively one instrument  for the detections and that some members of the LIGO group have been churlish when papers have been put out raising concerns about their work. Also that the group needs to put out materials explaining how they work with the noise produced in LIGO.
« Last Edit: 11/02/2018 11:09 PM by Star One »

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #297 on: 11/03/2018 10:57 AM »
In this week’s New Scientist magazine there is a special investigation casting doubt on the 2015 discovery of gravitational waves.
Not having read the article, I'll just note that the more recent detections, especially the corobborated neutron star mergers do imply that it was reasonable that the first detection was legit.

I do agree that more open data would be nice.
https://www.gw-openscience.org/events/ - does have some, but this is as I understand it all after their cleanup pipelines.
However, the cleanup pipeline to remove noise is going to be almost impenetrable without detailed knowledge of the instrument.

Also on that page is email notices to astronomers at the time of the releases, and their responses.
This is the most recent neutron star coalescance made public.
(to be clear, I have no insight on if there are unpublished events)

Quote from: LIGO
TITLE:   GCN CIRCULAR
NUMBER:  21505
SUBJECT: LIGO/Virgo G298048: Fermi GBM trigger 524666471/170817529: LIGO/Virgo Identification of a possible  gravitational-wave counterpart
DATE:    17/08/17 13:21:42 GMT
FROM:    Reed Clasey Essick at MIT  <[email protected]>

The LIGO Scientific Collaboration and the Virgo Collaboration report:

The online CBC pipeline (gstlal) has made a preliminary
identification of a GW candidate associated with the time
 of Fermi GBM trigger 524666471/170817529 at gps time 1187008884.47
 (Thu Aug 17 12:41:06 GMT 2017) with RA=186.62deg Dec=-48.84deg and an error radius of 17.45deg.

The candidate is consistent with a neutron star binary coalescence with
False Alarm Rate of ~1/10,000 years.

An offline analysis is ongoing. Any significant updates will be provided
by a new Circular.
« Last Edit: 11/03/2018 11:07 AM by speedevil »

Offline Star One

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Gravitational Waves Have Been Detected At LIGO
« Reply #298 on: 11/03/2018 02:11 PM »
The group even question the neutron star merger pointing out it was initially flagged as a false positive.

Here’s an abstract from the online version of the article, to see the full thing you have to be a subscriber.

https://www.newscientist.com/article/mg24032022-600-exclusive-grave-doubts-over-ligos-discovery-of-gravitational-waves/

But here’s an accessible article on the same matter.

https://arstechnica.com/science/2018/10/danish-physicists-claim-to-cast-doubt-on-detection-of-gravitational-waves/
« Last Edit: 11/03/2018 02:42 PM by Star One »

Offline matthewkantar

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #299 on: 11/03/2018 04:06 PM »
Suggesting fraud or incompetence may be a strategy to get better or earlier access to the data.

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