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Advanced LIGO has detected gravitational waves from a binaryblack hole collision/merger



 
 
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  #1  
Old February 12th 16, 09:04 AM posted to sci.physics.research,sci.astro.research
Jonathan Thornburg [remove -animal to reply][_3_]
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Default 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"

  #2  
Old February 12th 16, 09:53 AM posted to sci.physics.research,sci.astro.research
Jos Bergervoet
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Posts: 126
Default 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

  #3  
Old February 13th 16, 11:07 AM posted to sci.physics.research,sci.astro.research
Jonathan Thornburg [remove -animal to reply][_3_]
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Default 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"

  #4  
Old February 13th 16, 11:08 AM posted to sci.astro.research,sci.physics.research
Jonathan Thornburg [remove -animal to reply][_3_]
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Posts: 137
Default 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"

  #5  
Old February 13th 16, 11:08 AM posted to sci.physics.research,sci.astro.research
Gregor Scholten
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Default 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?

  #6  
Old February 13th 16, 05:39 PM posted to sci.physics.research,sci.astro.research
Oliver Jennrich
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Posts: 7
Default 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

  #7  
Old February 13th 16, 05:40 PM posted to sci.physics.research,sci.astro.research
Jos Bergervoet
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Posts: 126
Default 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

  #8  
Old February 13th 16, 07:45 PM posted to sci.physics.research,sci.astro.research
David Staup[_2_]
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Posts: 347
Default 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?





  #9  
Old February 13th 16, 10:33 PM posted to sci.physics.research,sci.astro.research
Steven Carlip
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Posts: 9
Default 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

  #10  
Old February 13th 16, 10:33 PM posted to sci.physics.research,sci.astro.research
Phillip Helbig
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Posts: 38
Default 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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