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Advanced LIGO has detected gravitational waves from a binaryblack hole collision/merger
The event is called GW150914.
This Nature page is a good summary http://www.nature.com/news/einstein-...t-last-1.19361 as is this LIGO page http://www.ligo.org/science/Publicat...0914/index.php The main discovery paper is: http://link.aps.org/doi/10.1103/PhysRevLett.116.061102 There are also a bunch of other papers published today, all linked from the LIGO page I gave aboe. -- -- "Jonathan Thornburg [remove -animal to reply]" Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA "There was of course no way of knowing whether you were being watched at any given moment. How often, or on what system, the Thought Police plugged in on any individual wire was guesswork. It was even conceivable that they watched everybody all the time." -- George Orwell, "1984" |
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Advanced LIGO has detected gravitational waves from a binaryblack hole collision/merger
On 2/12/2016 9:04 AM, Jonathan Thornburg [remove -animal to reply] wrote:
The event is called GW150914. This Nature page is a good summary http://www.nature.com/news/einstein-...t-last-1.19361 as is this LIGO page http://www.ligo.org/science/Publicat...0914/index.php The main discovery paper is: http://link.aps.org/doi/10.1103/PhysRevLett.116.061102 There are also a bunch of other papers published today, all linked from the LIGO page I gave aboe. Why are the 2 predicted curve in this picture slightly different? https://www.ligo.caltech.edu/image/ligo20160211a It seems like there is some added noise in the prediction (the thin lines) but not exactly the same in Hanford and Livingston. Of course it could be random noise added but that would seem to be pointless (why not just plot the noise-free prediction?) So it must be from some known source of disturbance, for which they did *not* correct the measured signal. Which brings us to the question: Are we really seeing the *raw data* here?! That would mean that it is indeed an extremely clear signal (and all the scary explanation that lots of "data-processing" is needed to see the waves, would fortunately be a bit exaggerated.) -- Jos |
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Advanced LIGO has detected gravitational waves from a binary black hole collision/merger
In sci.astro.research Jos Bergervoet wrote:
Why are the 2 predicted curve in this picture slightly different? https://www.ligo.caltech.edu/image/ligo20160211a It seems like there is some added noise in the prediction (the thin lines) but not exactly the same in Hanford and Livingston. Of course it could be random noise added but that would seem to be pointless (why not just plot the noise-free prediction?) So it must be from some known source of disturbance, for which they did *not* correct the measured signal. Which brings us to the question: Are we really seeing the *raw data* here?! Yes, those plots are rather confusing. Apart from any noise, the predicted curves *should* look a bit different for Hanford and Livingston, because the two detectors have slightly different orientations with respect to the incoming gravitational wave. (Each detector is horizontal with respect to the Earth's surface at its location, but they're in different locations.) The incoming gravitational wave is (to a *very* good approximation -- this source is 400 megaparsec away) a plane wave. The best plots I have seen so far of something close to the actual data are those in figure 6 in this paper https://dcc.ligo.org/P1500218/ (Judging from its format, length, and content, I suspect that this paper will appear in Physical Review D very soon.) [Even here some filtering has been done to remove noise at very low and very high frequencies where the detectors aren't very sensitive. They have also applied notch filters to remove (e.g.) 60Hz power-line noise and a few other discrete frequencies where the detector is noisy.] That would mean that it is indeed an extremely clear signal (and all the scary explanation that lots of "data-processing" is needed to see the waves, would fortunately be a bit exaggerated.) This signal is pretty strong, and could be seen in the data stream by eye if you looked in just the right place. (You can see this in the graphs I linked to above.) However, that wouldn't give much confidence that this was a real astrophysical signal as opposed to detector noise: the noise has complicated and time-varying statistical properties, and in some cases it can almost mimic a real gravitational-wave signal. More generally, (a) we don't want to miss any fainter signals that might be there, and (b) we don't want to "cry wolf" and give false alarms on what are really just detector noise The fancy data-analysis & statistics are all designed to do (and quantify) as much as possible of (a) and as little as possible of (b). ciao, -- -- Jonathan Thornburg Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA "There was of course no way of knowing whether you were being watched at any given moment. How often, or on what system, the Thought Police plugged in on any individual wire was guesswork. It was even conceivable that they watched everybody all the time." -- George Orwell, "1984" |
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Advanced LIGO has detected gravitational waves from a binary black hole collision/merger
There's a very nice and not-very-technical open-access account of this
discovery, including some interesting history, at http://physics.aps.org/articles/v9/17 Many of the science papers from this first event (GW150914) are now open-access at the arXiv. The easiest way to find them is probably via an author search on "LIGO Scientific Collaboration", http://arxiv.org/find/gr-qc/1/au:+Co.../0/1/0/all/0/1 As has been noted, the main discovery paper is at http://link.aps.org/doi/10.1103/PhysRevLett.116.061102 This is now http://arxiv.org/abs/1602.03837 In an earlier posting in this thread, I wrote The best plots I have seen so far of something close to the actual data are those in figure 6 in this paper https://dcc.ligo.org/P1500218/ (Judging from its format, length, and content, I suspect that this paper will appear in Physical Review D very soon.) This is now figure 6 (on pdf page 9) in http://arxiv.org/abs/1602.03840 ciao, -- -- "Jonathan Thornburg [remove -animal to reply]" Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA "There was of course no way of knowing whether you were being watched at any given moment. How often, or on what system, the Thought Police plugged in on any individual wire was guesswork. It was even conceivable that they watched everybody all the time." -- George Orwell, "1984" |
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Advanced LIGO has detected gravitational waves from a binary
What I'm really asking myself is:
That black hole collision took place in 1.3 billion light years distance, and is still detectable. How strong would the gravitational waves be if the collision had taken place in a much nearer location, e.g. in 1 million light years or 1000 light years distance? Strong enough to yield effects visible to bare eyes? Strong enough to destroy Earth? |
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Advanced LIGO has detected gravitational waves from a binary
Gregor Scholten writes:
What I'm really asking myself is: That black hole collision took place in 1.3 billion light years distance, and is still detectable. How strong would the gravitational waves be if the collision had taken place in a much nearer location, e.g. in 1 million light years About a factor 1300 stronger. or 1000 light years distance? About a factor 1300000 stronger. The 'strength' of a GW is its amplitude. And that is proportional to 1/d (as the energy is ~amplitude^2 and conservation of energy implies that each surface of a sphere A~d^2 sees the same energy passing through.) Strong enough to yield effects visible to bare eyes? Strong enough to destroy Earth? The detected signal has an amplitude of about 10^-21. Had it occurred in 1000Lj distance, we would have observed an amplitude of 10^-15. Assuming a perfect response by Earth, it would have changed the diameter (~10^4km) by about 10 nanometer. Not really Earth-shattering, if you excuse the pun. Could we have seen it optically? Lets assume that angles are affected roughly the same as length, positions of stars would have changed by ~pi frad or about 0.6 nanoarcsec. That is kind of small. The very best astrometric measurements we can expect from Gaia are about 10 *micro*arcsec, so a factor 20000 worse. -- Space - The final frontier |
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Advanced LIGO has detected gravitational waves from a binary
On 2/13/2016 11:08 AM, Gregor Scholten wrote:
What I'm really asking myself is: That black hole collision took place in 1.3 billion light years distance, and is still detectable. How strong would the gravitational waves be if the collision had taken place in a much nearer location, e.g. in 1 million light years or 1000 light years distance? Strong enough to yield effects visible to bare eyes? Strong enough to destroy Earth? Slightly raising the stakes, I think their gravitional waves would not destroy the earth, even if the two black holes were replacing the sun! (We would of course have to give the earth an 8 times higher orbital speed in the first place, to maintain its distance). The distance to the sun is about 10^14 times smaller, so the waves would be some 10^14 times stronger and the suspended mirrors in the LIGO detector would not move 4 atto-meter, as they did on Sep 14, but a whole 0.4mm! This doesn't look like more than a micro-earthquake so the earth would not be destroyed and even the delicate LIGO detector would easily survive this (but the presence of two black holes instead of the sun might cause other problems..) Comparing it to EM: we can detect the Pioneer spacecraft radio transmitter now that it is at 3 10^12 meter distance, What if we were 10^14 times closer? That would be comparable to holding a transmitting cell-phone at 1 cm from your ear (in fact its transmitter is just slightly stronger than the average cellphone, both are a few Watts). -- Jos |
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Advanced LIGO has detected gravitational waves from a binary
On 2/13/2016 10:40 AM, Jos Bergervoet wrote:
On 2/13/2016 11:08 AM, Gregor Scholten wrote: What I'm really asking myself is: That black hole collision took place in 1.3 billion light years distance, and is still detectable. How strong would the gravitational waves be if the collision had taken place in a much nearer location, e.g. in 1 million light years or 1000 light years distance? Strong enough to yield effects visible to bare eyes? Strong enough to destroy Earth? Slightly raising the stakes, I think their gravitional waves would not destroy the earth, even if the two black holes were replacing the sun! (We would of course have to give the earth an 8 times higher orbital speed in the first place, to maintain its distance). The distance to the sun is about 10^14 times smaller, so the waves would be some 10^14 times stronger and the suspended mirrors in the LIGO detector would not move 4 atto-meter, as they did on Sep 14, but a whole 0.4mm! This doesn't look like more than a micro-earthquake so the earth would not be destroyed and even the delicate LIGO detector would easily survive this (but the presence of two black holes instead of the sun might cause other problems..) Comparing it to EM: we can detect the Pioneer spacecraft radio transmitter now that it is at 3 10^12 meter distance, What if we were 10^14 times closer? That would be comparable to holding a transmitting cell-phone at 1 cm from your ear (in fact its transmitter is just slightly stronger than the average cellphone, both are a few Watts). This surprises me, the equivalent of 3 solar masses radiated away in less than a second from 96 million miles away and we wouldn't notice? |
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Advanced LIGO has detected gravitational waves from a binary
In article ,
Jos Bergervoet wrote: On 2/13/2016 11:08 AM, Gregor Scholten wrote: What I'm really asking myself is: That black hole collision took place in 1.3 billion light years distance, and is still detectable. How strong would the gravitational waves be if the collision had taken place in a much nearer location, e.g. in 1 million light years or 1000 light years distance? Strong enough to yield effects visible to bare eyes? Strong enough to destroy Earth? Slightly raising the stakes, I think their gravitional waves would not destroy the earth, even if the two black holes were replacing the sun! (We would of course have to give the earth an 8 times higher orbital speed in the first place, to maintain its distance). The distance to the sun is about 10^14 times smaller, so the waves would be some 10^14 times stronger and the suspended mirrors in the LIGO detector would not move 4 atto-meter, as they did on Sep 14, but a whole 0.4mm! I've been trying to figure out if we could *hear* the gravitational wave for a black hole merger at the distance of the Sun. According to a random internet source, the human ear can detect vibrations as small as 10^{-11} m. The trouble is that what a gravitational wave produces is strain, or relative changes in distance, and I don't know enough physiology to know what the relevant scale is. (If we can treat the outer ear as a resonant cavity, a strain of 10^{-7} would apparently be audible. But the relevant physiology might be different -- it might depend on displacements of the bones in the middle ear, or on the size of the inner ear... Anybody know an expert?) Steve Carlip |
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Advanced LIGO has detected gravitational waves from a binary
In article , David Staup
writes:=20 This surprises me, the equivalent of 3 solar masses radiated away in=20 less than a second from 96 million miles away and we wouldn't notice? It's not just the energy, but rather the effect it produces on whatever it interacts with (or not). Supernovae radiate a huge amount of energy in neutrinos, but these hardly affect anything else. This is a relatively violent event, and it needs an incredibly sensitive detector just to register it. With electromagnetic radiation, objects much farther away, almost at the edge of the observable universe, can be seen with essentially just a mirror which would fit into a (large) house---just a piece of glass. Keep in mind that the gravitational interaction is, compared with other interactions, very weak.=20 |
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