Author Topic: Gravitational Waves Have Been Detected At LIGO  (Read 148149 times)

Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #60 on: 02/11/2016 04:36 pm »
There's a very good article in Quanta:

https://www.quantamagazine.org/20160211-gravitational-waves-discovered-at-long-last/

That article actually confirms that another weaker signal was seen a few weeks later (and now I'm hearing that there's been "several" weaker signals).

Edit:

In this New York Times article Weiss confirms that there were at least four detections in the first run:

http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html?_r=0

Edit 2: fixed link
« Last Edit: 02/11/2016 04:53 pm by as58 »

Offline Rocket Science

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« Last Edit: 02/11/2016 04:53 pm by Rocket Science »
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Offline Robotbeat

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #62 on: 02/11/2016 04:59 pm »
Just a note: this discovery is a resounding confirmation of EXISTING physics theories, not new physics. It's new experimental evidence of the existing theory developed by Einstein 100 years ago.


LIGO may go on to discover new physics, but so far this is a resounding (heh) confirmation of our existing theories.
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Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #63 on: 02/11/2016 05:52 pm »
There's a very good article in Quanta:

https://www.quantamagazine.org/20160211-gravitational-waves-discovered-at-long-last/

That article actually confirms that another weaker signal was seen a few weeks later (and now I'm hearing that there's been "several" weaker signals).

Edit:

In this New York Times article Weiss confirms that there were at least four detections in the first run:

http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html?_r=0

Edit 2: fixed link

Binary Neutron stars? Which was the other phenomena they were looking to detect.
« Last Edit: 02/11/2016 05:53 pm by Star One »

Offline sanman

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #64 on: 02/11/2016 06:00 pm »
Binary Neutron stars? Which was the other phenomena they were looking to detect.

Probably supernovae?

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #65 on: 02/11/2016 06:07 pm »
[continues the paper highlights from this post http://forum.nasaspaceflight.com/index.php?topic=39297.msg1490602#msg1490602]

- Spin of the primary black hole is reasonably well understood, while the second's is weakly constrained.

- 3.0±0.5 solar masses (x c^2) were released exclusively in the form of gravitational waves (which ties into the previous discussion about artificial production).

- A Kerr (rotating) black hole is the result from the merger, and the signal is consistent with expectations.

- Graviton mass constraint: m_g < 1.2·10^-22 eV/c^2 (lower than that of the photon, FWIW). Better limits were already achieved with other model dependent bounds, but not with independently-observed ones.

- This is a direct proof of the existence of dozen-solar-mass class black holes, the existence of binaries and capability of merging. This wasn't proven before.

- It is expected there is a constant gravitational wave background of orbiting binaries which permeates the Universe. A large single wave has been detected, but there is a stormy sea underneath.
-DaviD-

Offline notsorandom

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #66 on: 02/11/2016 06:11 pm »
- 3.0±0.5 solar masses (x c^2) were released exclusively in the form of gravitational waves (which ties into the previous discussion about artificial production).
What would that even look like up close? What would that intensity of gravitational wave energy do to things?

Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #67 on: 02/11/2016 06:11 pm »
Another in-depth, behind-the-scenes article:

http://www.newyorker.com/tech/elements/gravitational-waves-exist-heres-how-scientists-finally-found-them

Seems that many reporters have received the word in advance under embargo.

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #68 on: 02/11/2016 06:12 pm »
Argentinians not only deploy huge flags on Arianespace launches, but also huge foulards in science press conferences  ;D
-DaviD-

Offline gosnold

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #69 on: 02/11/2016 06:18 pm »
How do they know the distance between us and the event?

Offline sanman

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #70 on: 02/11/2016 06:18 pm »
Will Gravitational Astronomy help us to verify Dark Matter? That's supposed to have mass, but is otherwise undetectable on the EM spectrum.
Would it be possible for Gravitational Astronomy to differentiate between Dark Matter and regular matter - perhaps by cross-referencing with classical forms of astronomical observation?
« Last Edit: 02/11/2016 06:29 pm by sanman »

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #71 on: 02/11/2016 06:19 pm »
- 3.0±0.5 solar masses (x c^2) were released exclusively in the form of gravitational waves (which ties into the previous discussion about artificial production).
What would that even look like up close? What would that intensity of gravitational wave energy do to things?

I have no idea of the subtleties (and I hope to never discover firsthand ;) ) but for sure you'd see a "stretching" of depth/height/width with the observed frequency (35-100 Hz). So stretching also my imagination, I suppose you'd see a kind of flickering of "reality" by which it would be difficult to judge distances. Time distortions would possibly average out in "human" timescales.

I don't think the amplitude of the distortions, even relatively close, would be enough to see something "by eye" though. You'd probably need to be really up close to the binary, in which case there would be plenty of other effects. Since deformed space leaves matter particles relatively unaffected, if the amplitude of the waves was big enough it would possibly rip things apart, maybe even atoms themselves.
-DaviD-

Offline Rodal

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #72 on: 02/11/2016 06:22 pm »
Argentinians not only deploy huge flags on Arianespace launches, but also huge foulards in science press conferences  ;D
And they also did better than Spain and Italy at the last World Soccer Cup  ;)

Argentina #2
Italy and Spain did not make into the round of 16
Best player: Lionel Messi

Offline Rodal

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #73 on: 02/11/2016 06:24 pm »
Quote
February 11, 2016

Dear MIT graduate,

At about 10:30 this morning in Washington, D.C., MIT, Caltech and the National Science Foundation (NSF) will make a historic announcement in physics: the first direct detection of gravitational waves, a disturbance of space-time that Albert Einstein predicted a century ago.

You can read an overview of the discovery here as well as an interview with MIT Professor Emeritus Rainer Weiss PhD '62, instigator and a leader of the Laser Interferometer Gravitational-Wave Observatory (LIGO) effort.

The beauty and power of basic science
I do not typically write to you to celebrate individual research achievements, no matter how impressive; our community produces important work all the time. But I urge you to reflect on today’s announcement because it demonstrates, on a grand scale, why and how human beings pursue deep scientific questions – and why it matters.

Today's news encompasses at least two compelling stories.

First is the one the science tells: that with his theory of general relativity, Einstein correctly predicted the behavior of gravitational waves, space-time ripples that travel to us from places in the universe where gravity is immensely strong. Those rippling messages are imperceptibly faint; until now, they had defied direct observation. Because LIGO succeeded in detecting these faint messages – from two black holes that crashed together to form a still larger one – we have remarkable evidence that the system behaves exactly as Einstein foretold.

With even the most advanced telescopes that rely on light, we could not have seen this spectacular collision, because we expect black holes to emit no light at all. With LIGO's instrumentation, however, we now have the "ears" to hear it. Equipped with this new sense, the LIGO team encountered and recorded a fundamental truth about nature that no one ever has before. And their explorations with this new tool have only just begun. This is why human beings do science!

The second story is of human achievement. It begins with Einstein: an expansive human consciousness that could form a concept so far beyond the experimental capabilities of his day that inventing the tools to prove its validity took a hundred years.

That story extends to the scientific creativity and perseverance of Rai Weiss and his collaborators. Working for decades at the edge of what was technologically possible, against the odds Rai led a global collaboration to turn a brilliant thought experiment into a triumph of scientific discovery.

Important characters in that narrative include the dozens of outside scientists and NSF administrators who, also over decades, systematically assessed the merits of this ambitious project and determined the grand investment was worth it. The most recent chapter recounts the scrupulous care the LIGO team took in presenting these findings to the physics community. Through the sacred step-by-step process of careful analysis and peer-reviewed publication, they brought us the confidence to share this news – and they opened a frontier of exploration.

At a place like MIT, where so many are engaged in solving real-world problems, we sometimes justify our nation's investment in basic science by its practical byproducts. In this case, that appears nearly irrelevant. Yet immediately useful "results" are here, too: LIGO has been a strenuous training ground for thousands of undergraduates and hundreds of PhDs – two of them now members of our faculty.

What's more, the LIGO team's technological inventiveness and creative appropriation of tools from other fields produced instrumentation of unprecedented precision. As we know so well at MIT, human beings cannot resist the lure of a new tool. LIGO technology will surely be adapted and developed, "paying off" in ways no one can yet predict. It will be fun to see where this goes.
 
*        *        *
The discovery we celebrate today embodies the paradox of fundamental science: that it is painstaking, rigorous and slow – and electrifying, revolutionary and catalytic. Without basic science, our best guess never gets any better, and "innovation" is tinkering around the edges. With the advance of basic science, society advances, too.

I am proud and grateful to belong to a community so well equipped to appreciate the beauty and meaning of this achievement – and primed to unlock its opportunities.

In wonder and admiration,

L. Rafael Reif

Offline eeergo

Re: Gravitational Waves Have Been Detected At LIGO
« Reply #74 on: 02/11/2016 06:27 pm »
How do they know the distance between us and the event?

It is a model-dependent determination (meaning it's based on assumptions), considering the standard cosmological models (ostensibly ΛCDM refined with Planck data).

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.
-DaviD-

Offline ugordan

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #75 on: 02/11/2016 06:31 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.
« Last Edit: 02/11/2016 06:33 pm by ugordan »

Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #76 on: 02/11/2016 06:32 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.

Offline Star One

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #77 on: 02/11/2016 06:41 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?
« Last Edit: 02/11/2016 06:42 pm by Star One »

Offline sanman

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #78 on: 02/11/2016 06:42 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?

Offline as58

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Re: Gravitational Waves Have Been Detected At LIGO
« Reply #79 on: 02/11/2016 06:43 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.
« Last Edit: 02/11/2016 06:54 pm by as58 »

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