Author Topic: Gravitational Waves Have Been Detected At LIGO  (Read 148133 times)

Offline ugordan

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #80 on: 02/11/2016 06:44 pm »
Isn't that what they need the third detector to come online for to help with this?

They need it to better be able to triangulate the source direction in the sky. The more the better.

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #81 on: 02/11/2016 06:45 pm »
How do they know the distance between us and the event?

Isn't that what they need the third detector to come online for to help with this?

That's for directionality.
-DaviD-

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #82 on: 02/11/2016 06:45 pm »
They measured the redshift (I'm not sure how, since this event was not accompanied by electromagnetic (i.e. light/X-ray/UV...) detection, so it's not obvious to me what reference they used for "redshifted gravitational waves" - maybe Jonathan can help? :) ) and, assuming this standard Universe expansion model, got a distance value that would cause that redshift. This turned out to be between 250 and 570 megaparsecs.

Aren't these ultra-violent astrophysical events like Supernova explosions and Black Hole collisions supposed to give off gamma-ray bursts at the same time? Shouldn't they have detected an accompanying gamma-ray burst signal simultaneously in connection with the gravity waves?

Not if they're non-accreting.
-DaviD-

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #83 on: 02/11/2016 06:53 pm »
Isn't that what they need the third detector to come online for to help with this?

They need it to better be able to triangulate the source direction in the sky. The more the better.

Judging by the article they should have five soon.

Quote
Sir Alex Ferguson
Sir Alex Ferguson –  ‏@Furious_Fergie

Just had Wayne Rooney on the phone asking if gravitational waves are like Mexican waves.

I just said aye.

https://mobile.twitter.com/Furious_Fergie/status/697866904019582979

http://xkcd.com/1642/
« Last Edit: 02/11/2016 07:00 pm by Star One »

Offline notsorandom

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #84 on: 02/11/2016 06:57 pm »
What would that even look like up close? What would that intensity of gravitational wave energy do to things?

Unless I messed up my back-of-the-envelope calculations, even only 1 AU from the black hole pair the strain would be at parts per billion level.
I did some back of the envelope calculations myself that could be wrong. The energy this event unleashed was within a couple of orders of magnitude to what a supernova releases. Of course a supernova releases that energy not as gravitational waves but as thermal, electromagnetic, and neutrino radiation. This event released that much energy purely as gravitational waves. A supernova will ruin anyone's day within several dozens of light years. It is odd to think of that much energy being released and not harming anything a light year or further away let alone being inseparable.
« Last Edit: 02/11/2016 06:58 pm by notsorandom »

Offline Rocket Science

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #85 on: 02/11/2016 07:04 pm »
Einstein was right...again! ;D
"The laws of physics are unforgiving"
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Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #86 on: 02/11/2016 07:21 pm »
Jaunty MIT video.


Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #87 on: 02/11/2016 07:23 pm »
Actually it's more like 4 orders of magnitude... https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy) but I agree with the idea :0
« Last Edit: 02/11/2016 07:23 pm by eeergo »
-DaviD-

Offline Kimight

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #88 on: 02/11/2016 07:58 pm »
If my understanding is correct; the energy contained in the waves can be be measured either by the frequency or amplitude of these waves. I am however quite curious as to how LIGO would fare if the waves hit the detectors at an angle of (pi/4) or (5*pi/4). Assuming of course the two detectors are at an angle of (pi/2).

My guess is that they can calculate time dilations since they know the length of the detectors and the speed of light, but wouldn't a third detector increase the ability to filter out noise with better accuracy, even better than having multiple detectors scattered around the world?
« Last Edit: 02/11/2016 08:14 pm by Kimight »

Offline notsorandom

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #89 on: 02/11/2016 08:06 pm »
Actually it's more like 4 orders of magnitude... https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy) but I agree with the idea :0
There is a neutrino pulse in core collapse supernovas that has about 1046 Joules though some of his gets reabsorbed in the process of the collapse driving the explosion. It is crazy to think about an explosion driven by a particle that rarely interacts with anything.

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #90 on: 02/11/2016 09:22 pm »
Very good New Yorker article not just on the project's history, but also confirms other weaker signals are coming down the line.

http://www.newyorker.com/tech/elements/gravitational-waves-exist-heres-how-scientists-finally-found-them
« Last Edit: 02/11/2016 09:22 pm by Star One »

Online FinalFrontier

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #91 on: 02/11/2016 10:40 pm »
Another article
http://www.sciencemag.org/news/2016/02/gravitational-waves-einstein-s-ripples-spacetime-spotted-first-time

This is so exciting. We might finally be getting closer to understanding how and what gravity actually is. If we can crack that nut it may eventually be possible for us to get to make artificial gravity a thing. That would have HUGE impacts for our entire civilization, but the biggest hurdle so far has even been understanding how gravity works and what exactly gravity is. Now we are solving that. Congratulations to the LIGO teams!
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Offline Robotbeat

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #92 on: 02/11/2016 11:41 pm »
Another article
http://www.sciencemag.org/news/2016/02/gravitational-waves-einstein-s-ripples-spacetime-spotted-first-time

This is so exciting. We might finally be getting closer to understanding how and what gravity actually is. If we can crack that nut it may eventually be possible for us to get to make artificial gravity a thing. That would have HUGE impacts for our entire civilization, but the biggest hurdle so far has even been understanding how gravity works and what exactly gravity is. Now we are solving that. Congratulations to the LIGO teams!
Currently, we are finding that the "graviton" is basically massless. This basically confirms our theories. So far, this LIGO detection is pounding more nails in the coffin of the idea of artificial gravity and other hypothetical phenomenon that require new physics. We HOPE new discoveries start to pull some of those nails out, but the recent announcement was another one pounded in.
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Offline RonM

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #93 on: 02/12/2016 01:10 am »
Another article
http://www.sciencemag.org/news/2016/02/gravitational-waves-einstein-s-ripples-spacetime-spotted-first-time

This is so exciting. We might finally be getting closer to understanding how and what gravity actually is. If we can crack that nut it may eventually be possible for us to get to make artificial gravity a thing. That would have HUGE impacts for our entire civilization, but the biggest hurdle so far has even been understanding how gravity works and what exactly gravity is. Now we are solving that. Congratulations to the LIGO teams!
Currently, we are finding that the "graviton" is basically massless. This basically confirms our theories. So far, this LIGO detection is pounding more nails in the coffin of the idea of artificial gravity and other hypothetical phenomenon that require new physics. We HOPE new discoveries start to pull some of those nails out, but the recent announcement was another one pounded in.

Good point. Maybe more observations will find some deviation from GR, but isn't two colliding black holes as strong of a test as possible?

Congratulations LIGO teams. Another great day for science.

Offline Rocket Science

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Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #95 on: 02/12/2016 08:03 am »

Another article
http://www.sciencemag.org/news/2016/02/gravitational-waves-einstein-s-ripples-spacetime-spotted-first-time

This is so exciting. We might finally be getting closer to understanding how and what gravity actually is. If we can crack that nut it may eventually be possible for us to get to make artificial gravity a thing. That would have HUGE impacts for our entire civilization, but the biggest hurdle so far has even been understanding how gravity works and what exactly gravity is. Now we are solving that. Congratulations to the LIGO teams!
Currently, we are finding that the "graviton" is basically massless. This basically confirms our theories. So far, this LIGO detection is pounding more nails in the coffin of the idea of artificial gravity and other hypothetical phenomenon that require new physics. We HOPE new discoveries start to pull some of those nails out, but the recent announcement was another one pounded in.

But you're rather forgetting that quantum physics also appears, through increasing experimental evidence, to do lots of things that Einstein really didn't like. I am more confident that this realm will be the one where things will get interesting.

Offline rokan2003

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #96 on: 02/12/2016 08:16 am »
Gbgs

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #97 on: 02/12/2016 09:35 am »
Because yesterday's excitement wasn't enough... turns out the Fermi observatory **might** have detected a coincident GRB, which is unexpected for this kind of merger ! Here's the technical paper preprint:

http://gammaray.nsstc.nasa.gov/gbm/publications/preprints/gbm_ligo_preprint.pdf

PS: Swift didn't see anything but the source's favored regions from LIGO and GLAST were either obscured by the Sun or not in the instrument's FOV.
« Last Edit: 02/12/2016 10:17 am by eeergo »
-DaviD-

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #98 on: 02/12/2016 02:47 pm »
And no coincident neutrinos were detected by either Antares (the neutrino detector, not the rocket :) ) or ICECube:

https://dcc.ligo.org/public/0123/P1500271/013/GW150914_neutrino.pdf (paper)
http://icecube.wisc.edu/news/view/398

PS: I just saw the same links posted in the "Space Science" subforum thread. I will keep these here, but if they are merged my posts are redundant since I wrote them several hours after the other guys'. Moderators please delete this and the previous post if you're merging the treads.
« Last Edit: 02/12/2016 03:17 pm by eeergo »
-DaviD-

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #99 on: 02/12/2016 03:04 pm »
How do they know the distance between us and the event?

If I understood it correctly, using the observed shape of the waveform one can infer the masses involved and then the theory also gives you the energy (or power?) radiated. Then you go back to the observed amplitude of the oscillations (a.k.a. the local "strain") and, via the inverse square law, can work out the distance. With a certain error bar, of course.

Yes, that gives the luminosity distance (for very far away objects there are several "distances"). They just convert the luminosity distance to redshift, because that's what everyone is used to in cosmology/extragalactic astronomy.

Edit: The conversion from luminosity distance to redshift does depend on the cosmological model as eeergo mentioned, but in this case the merger was close enough so that it doesn't have a large effect.

I found some more details on this in the source characterization paper: https://dcc.ligo.org/LIGO-P1500218/public/main

Quote
The observed frequency of the signal is redshifted by a factor of (1 + z),  where z is the cosmological redshift. There is no intrinsic mass or length scale in vacuum general relativity, and the dimensionless quantity that incorporates frequency is fGm/c^3. Consequently, a redshifting of frequency is indistinguishable from a rescaling of the masses by the same factor. We therefore measure redshifted masses m,  which are related to source frame masses by m= (1 + z)·m_source. However, the GW amplitude A_GW,  Eq. (2),  also scales linearly with the mass and is inversely proportional to the comoving distance in an expanding universe. This implies that A_GW ~ 1/D_L and from the GW signal alone we can directly measure the luminosity distance, but not the redshift.

The  observed time delay, and the need for the  registered signal at the two sites to be consistent in amplitude and phase, allow us to localize the source to a ring on the sky [34, 35].  Where there is no precession, changing the
viewing angle of the system simply changes the observed waveform by an overall amplitude and phase. Furthermore,
the two polarizations are the same up to overall amplitude and phase. Thus, for systems with minimal precession, the
distance, binary orientation, phase at coalescence and sky location  of  the  source  change  the  overall  amplitude  and
phase of the source in each detector, but they do not change the signal morphology.  Phase and amplitude consistency
allow us to untangle some of the geometry of the source. If the binary is precessing, the GW amplitude and phase have
a complicated dependency on the orientation of the binary, which provides additional information.
-DaviD-

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