Author Topic: Gravitational Waves Have Been Detected At LIGO  (Read 87291 times)

Offline hop

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #300 on: 11/03/2018 06:36 PM »
The group even question the neutron star merger pointing out it was initially flagged as a false positive.
As the Ars article points out, Jackson's group has actually been pushing this for several years, and don't appear to have gotten much traction in the broader community. New Scientist pushing it as an "exclusive" seems pretty clickbaity. Maybe there's some new paper or detail, but basic outline doesn't seem to be at all new.

Offline Star One

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Gravitational Waves Have Been Detected At LIGO
« Reply #301 on: 11/03/2018 07:41 PM »
The group even question the neutron star merger pointing out it was initially flagged as a false positive.
As the Ars article points out, Jackson's group has actually been pushing this for several years, and don't appear to have gotten much traction in the broader community. New Scientist pushing it as an "exclusive" seems pretty clickbaity. Maybe there's some new paper or detail, but basic outline doesn't seem to be at all new.

As I said I’ve only skimmed it so far but there is this paragraph in it.

Quote
And there are legitimate questions about that trust. New Scientist has learned, for instance, that the collaboration decided to publish data plots that were not derived from actual analysis. The paper on the first detection in Physical Review Letters used a data plot that was more “illustrative” than precise, says Cornish. Some of the results presented in that paper were not found using analysis algorithms, but were done “by eye”.
« Last Edit: 11/03/2018 07:42 PM by Star One »

Offline LouScheffer

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #302 on: 11/05/2018 03:08 PM »
The group even question the neutron star merger pointing out it was initially flagged as a false positive.
This in particular fails the smell test.

First, the Fermi gamma ray observatory detected a GRB co-incident within 2 seconds.  That's low probability for a false alarm right there.

And crucially VIRGO saw the same event, at the same time, within a few milliseconds (as expected).  So now we have the same event detected within a few milliseconds in Washington, Louisiana, and Italy.  That's incredibly unlikely for a false positive.

And most important, using the VIRGO and LIGO data, they estimated where to look.  When they did so, the optical telescopes found an extremely rare and transient event, a kilo-nova, not known to be seen before.  If the LIGO and VIRGO events were false alarms, this would imply that this was just luck.  But the same telescopes are in use all the time, and have not seen many (any?) corresponding events.  So seeing such a rare event, just where and when LIGO said to look, would be an incredible coincidence.

So the gravitational waves from the neutron star collision are established beyond any reasonable doubt.

Offline jgoldader

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #303 on: 11/05/2018 09:36 PM »

This in particular fails the smell test.

First, the Fermi gamma ray observatory detected a GRB co-incident within 2 seconds.  That's low probability for a false alarm right there.

And crucially VIRGO saw the same event, at the same time, within a few milliseconds (as expected).  So now we have the same event detected within a few milliseconds in Washington, Louisiana, and Italy.  That's incredibly unlikely for a false positive.

And most important, using the VIRGO and LIGO data, they estimated where to look.  When they did so, the optical telescopes found an extremely rare and transient event, a kilo-nova, not known to be seen before.  If the LIGO and VIRGO events were false alarms, this would imply that this was just luck.  But the same telescopes are in use all the time, and have not seen many (any?) corresponding events.  So seeing such a rare event, just where and when LIGO said to look, would be an incredible coincidence.

So the gravitational waves from the neutron star collision are established beyond any reasonable doubt.

Well... LIGO saw it, but Virgo didn't, which helped pin down the source location.  See https://www.ligo.org/detections/GW170817/paper/GW170817-PRLpublished.pdf

But the GW detection for this source was very different from the earlier BH mergers; it lasted ~30 seconds, as expected for a NS merger, instead of the fraction of a second of the BH merger candidates.  So you have a detection that looked like a NS merger, with the first GRB associated with a GW detection, in the GW error ellipse, and the optical transient that looked like the expectations of a NS merger... that's a lot of coincidences for it to not be a real association.

I would expect that when LIGO/VIRGO are both back online, we'll have more detections, some from both observatories, and that will probably close the case.  If we don't get simultaneous detections...
Recovering astronomer

Offline LouScheffer

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #304 on: 11/06/2018 12:08 AM »

And crucially VIRGO saw the same event, at the same time, within a few milliseconds (as expected).  So now we have the same event detected within a few milliseconds in Washington, Louisiana, and Italy.  That's incredibly unlikely for a false positive.

And most important, using the VIRGO and LIGO data, they estimated where to look.  [...]

So the gravitational waves from the neutron star collision are established beyond any reasonable doubt.

Well... LIGO saw it, but Virgo didn't, which helped pin down the source location.  See https://www.ligo.org/detections/GW170817/paper/GW170817-PRLpublished.pdf

VIRGO *did* see the event, but with a low signal-to-noise (just 2.0).  This was not enough to claim an independent detection, but did help in narrowing down the search box.  From the article above,
Quote
The combined SNR of GW 170817 is estimated to be 32.4, with values 18.8, 26.4, and 2.0 in the LIGO-Hanford, LIGO-Livingston, and VIRGO data respectively.

Offline jebbo

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #305 on: 11/06/2018 06:11 AM »
I would expect that when LIGO/VIRGO are both back online, we'll have more detections, some from both observatories, and that will probably close the case.  If we don't get simultaneous detections...

I think there is about a 2x improvement in the next observing run, which (from memory; I'll try and dig out the source) means they expect a detection about once a week.

--- Tony

Offline Star One

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Gravitational Waves Have Been Detected At LIGO
« Reply #306 on: 11/06/2018 07:56 AM »
I have a feeling that the other scientists supporting them in the New Scientist article but indications that they still believe that GW will be confirmed are actually looking to prise open what is perceived as the LIGO collaboration overly secretive analysis methods. Especially important as it says in the article that LIGO are the only ones with the detector, and it cannot be independently verified.
« Last Edit: 11/06/2018 08:03 AM by Star One »

Offline LouScheffer

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #307 on: 11/06/2018 02:30 PM »
I have a feeling that the other scientists supporting them in the New Scientist article but indications that they still believe that GW will be confirmed are actually looking to prise open what is perceived as the LIGO collaboration overly secretive analysis methods.
This is not unusual for big science.  I'm working on a project that, while not LIGO or CERN scale, is still 10s of millions of $$ over many years.  I'm all for releasing data as we acquire it and tools as we develop them, but I'm in the distinct minority,.   The grad students and postdocs are scared that someone will take a quick look at the data and scoop some phenomena they need for either a thesis or top-journal papers they need to get an academic position.  The higher management wants a big unified data/PR release, so they get a big splash for all the money they spent, rather than an un-memorable sequence of smaller releases.  And (unfortunately in my mind) acquiring the data does not get nearly the credit as analyzing it. so if a project spends $$$ on acquiring data, then in return they want to be the first to analyze it.  And they naturally want to do a thorough job, not just a quick look, so the data stays private even longer.

I personally believe the risk of adverse events is low, and science would be better served by faster release.   But I can remember worrying about being scooped as a grad student (I was quite relieved when I presented my work at a conference, since that established priority).  It's also understandable that the folks who provide the big bucks want the credit to go to their group, who have invested not only dollars but many years of their time.  So this is likely a tradeoff that is needed to get the big bucks for big projects.



 

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #308 on: 11/06/2018 08:14 PM »
I have a feeling that the other scientists supporting them in the New Scientist article but indications that they still believe that GW will be confirmed are actually looking to prise open what is perceived as the LIGO collaboration overly secretive analysis methods.
This is not unusual for big science.  I'm working on a project that, while not LIGO or CERN scale, is still 10s of millions of $$ over many years.  I'm all for releasing data as we acquire it and tools as we develop them, but I'm in the distinct minority,.   The grad students and postdocs are scared that someone will take a quick look at the data and scoop some phenomena they need for either a thesis or top-journal papers they need to get an academic position.  The higher management wants a big unified data/PR release, so they get a big splash for all the money they spent, rather than an un-memorable sequence of smaller releases.  And (unfortunately in my mind) acquiring the data does not get nearly the credit as analyzing it. so if a project spends $$$ on acquiring data, then in return they want to be the first to analyze it.  And they naturally want to do a thorough job, not just a quick look, so the data stays private even longer.

I personally believe the risk of adverse events is low, and science would be better served by faster release.   But I can remember worrying about being scooped as a grad student (I was quite relieved when I presented my work at a conference, since that established priority).  It's also understandable that the folks who provide the big bucks want the credit to go to their group, who have invested not only dollars but many years of their time.  So this is likely a tradeoff that is needed to get the big bucks for big projects.

Thank you for that info. In the case of the LIGO though it sounds like it has engendered suspicion of their methods in others.

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #309 on: 11/23/2018 10:41 AM »
KAGRA is expected to join the global GW array in about a year's time, about halfway through LIGO and VIRGO's O3 campaign, in its "baseline" (bKAGRA) configuration.

https://arxiv.org/pdf/1811.08079.pdf
-DaviD-

Offline jebbo

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #310 on: 12/03/2018 08:15 AM »
Important update with four new detections!

GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs

Quote
We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1M⊙ during the first and second observing runs of the Advanced gravitational-wave detector network. During the first observing run (O1), from September 12th, 2015 to January 19th, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30th, 2016 to August 25th, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818 and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6+3.1−0.7M⊙, and 85.1+15.6−10.9M⊙, and range in distance between 320+120−110 Mpc and 2750+1350−1320 Mpc. No neutron star - black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of 110 - 3840 Gpc−3y−1 for binary neutron stars and 9.7 - 101 Gpc−3y−1 for binary black holes, and determine a neutron star - black hole merger rate 90% upper limit of 610 Gpc−3y−1.

Arxiv paper

--- Tony

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #311 on: 12/03/2018 08:49 AM »
Important update with four new detections!

Quote
. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false alarm rate less than 1 per 30 days. .
They believe if they understand the instrument properly, they should have seen under five of these marginal events. While they can't say for certain that any particular one of them is meaningful - they believe the fact they saw 14 means at least some may be real adding constraints on the event rate.

For the next observing run, they plan on not requiring people who they are sharing the data with to sign agreements to keep it secret.
https://wiki.gw-astronomy.org/OpenLVEM/WebHome
Quote
This is the community forum on multi-messenger observations connected to Gravitational Wave (GW) transient event detections. This forum has no requirements for participation -- anyone interested can join. This open forum started in January 2018. The LIGO-Virgo Collaboration will use this forum to communicate and interact with the community.

The next test run begins in december for a week or so, then O3 begins in March or so and will run for one year.

Quote
The next event of interest will be our engineering run ER13, planned for 14 Dec 2018 08:00 US Pacific time to 18 December 06:00 US Pacific time.
https://www.ligo.caltech.edu/page/observatory-status
« Last Edit: 12/03/2018 09:10 AM by speedevil »

Offline jebbo

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Offline jebbo

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #313 on: 12/03/2018 12:46 PM »
And another. This time a visualisation of the sky position of all the detections

https://twitter.com/LIGO/status/1069587054571458560

Offline Star One

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Gravitational Waves Have Been Detected At LIGO
« Reply #314 on: 12/04/2018 07:54 AM »
LIGO to publish new paper in wake of New Scientist investigation

Quote
The LIGO Scientific Collaboration, which detected gravitational waves in 2015, has announced that it will publish a detailed explanation of how it analyses the noise in its detectors.

The announcement, on 1 November, comes in the wake of an exclusive New Scientist investigation that exposed questions about the analysis underpinning the breakthrough discovery.

The fact that they are going to do this certainly seems to indicate that those on here and elsewhere who thought there was no case to answer were wrong.
« Last Edit: 12/04/2018 07:58 AM by Star One »

Offline speedevil

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #315 on: 12/06/2018 02:10 AM »
The fact that they are going to do this certainly seems to indicate that those on here and elsewhere who thought there was no case to answer were wrong.
Or that the team involved wanted to get the papers with actual data out before going into a 'how we did it' paper that would presumably not be nearly as highly cited because the number of people outside LIGO with meaningful gravitational detectors is zero.

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #316 on: 12/06/2018 03:11 PM »
The fact that they are going to do this certainly seems to indicate that those on here and elsewhere who thought there was no case to answer were wrong.
Or that the team involved wanted to get the papers with actual data out before going into a 'how we did it' paper that would presumably not be nearly as highly cited because the number of people outside LIGO with meaningful gravitational detectors is zero.

To me the important thing is that it is being written. Except with a small minority I don’t think people were believing they hadn’t detected gravitational waves, more the case of please show us your working out.

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