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



 
 
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  #11  
Old February 13th 16, 11:15 PM posted to sci.physics.research,sci.astro.research
J. J. Lodder
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Posts: 53
Default Advanced LIGO has detected gravitational waves from a binary

David Staup wrote:

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?


We would certainly notice a change in the orbit of the earth,
some time later, from the missing mass.
I haven't done the sums, but I feel confident
that the signal should also be visible
in the instantaneous earth-moon distance,
if the lunar laser reflectors were being operated.

The effects would also be immediately visible in GPS,

Jan



  #12  
Old February 15th 16, 09:22 AM posted to sci.physics.research,sci.astro.research
Keith F. Lynch
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Posts: 48
Default Advanced LIGO has detected gravitational waves from a binary

Phillip Helbig (undress to reply) wrote:
David Staup writes:=20
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?


It's not just the energy, but rather the effect it produces on
whatever it interacts with (or not).


Right. I just ran some numbers, and I came to the remarkable
conclusion that the total solar power output (4E+26 watts) could
harmlessly pass through you if it was in the form of gravitational
waves rather than heat and light.

I used the formula c^3 h^2 f^2 pi / (8 G) to convert strain to flux.
G is the gravitational constant, h is the strain, c is the speed of
light, and f is the frequency in Hz (250 in this case). The peak
strain of the recent event was 1E-21, so I get a peak flux of 10
milliwatts per square meter.

No wonder they always list the sensitivity of LIGO in terms of strain
rather than in terms of watts per square meter. The latter doesn't
sound nearly as impressive! Indeed, if the event had given off light
rather than gravitation waves, it would have been not only bright
enough to see from here, but bright enough to read by!

As a sanity check, I divided the reported peak power output of the
event, 3.6E49 watts, i.e. 200 solar masses per second annihilated, by
the area of a sphere 1.3 billion light years in radius. I get about
20 milliwatts per square meter. What accounts for the factor of two
discrepancy? Probably polarization. LIGO, if I understand correctly,
is sensitive to only one of the two polarizations.

("Only" 3 solar masses were annihilated, because the event lasted less
than a second.)

Lets get closer to the event and see what happens. I hope you're
reading this with a fixed font.

Distance flux (W/m^2) strain N

1.3E25 m (1.3E9 ly) 1E-2 1E-21 4E33
1.3E22 m (1.3E6 ly) 1E+4 1E-18 4E39
1.3E19 m (1.3E3 ly) 1E+10 1E-15 4E45
1.3E16 m (1.3 ly) 1E+16 1E-12 4E51
1.3E13 m (66 AU) 1E+22 1E-9 4E57
1.3E10 m (8 M miles) 1E+28 1E-6 4E63

The last column is the number of gravitons per square meter per
second. I get that by multiplying the flux by the frequency and
dividing by Plank's constant.

In each case, I assume you're floating in space, in a good spacesuit,
facing toward the event.

I assume that a strain of one part in a million isn't going to hurt
you, especially if it's front-to-back rather than head-to-toes. Note
that that last distance is much less than 1 AU. 1E+28 watts per
square meter -- your cross-sectional area is probably roughly one
square meter -- means 25 times the sun's total power output is going
through you. I wonder what it would feel like.

Of course I'm also assuming it was a "clean" event, i.e. nothing but
gravitational waves was given off. If it consisted of nothing but two
black holes, that's pretty much certain. But if there was other stuff
in the area, all bets are off. Indeed, there was a weak gamma ray
burst half a second after the event, which may or may not be a
coincidence. We don't know the direction of either the event or
the gamma ray burst, except very roughly.

Supernovae radiate a huge amount of energy in neutrinos, but these
hardly affect anything else.


Neutrinos aren't nearly as stealthy as gravitons. According to
Randall Munroe, a typical supernova will emit 1E57 neutrinos, and
they will be lethal at about 2 AU. During the peak tenth of a second
of the event at the closest distance I list, 100,000 times as many
gravitons will harmlessly pass through you as the *total* number
of neutrinos given off by a supernova!

--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

  #13  
Old February 15th 16, 10:55 PM posted to sci.physics.research,sci.astro.research
Keith F. Lynch
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Posts: 48
Default Advanced LIGO has detected gravitational waves from a binary

Keith F. Lynch wrote:
As a sanity check, I divided the reported peak power output of the
event, 3.6E49 watts, i.e. 200 solar masses per second annihilated,
by the area of a sphere 1.3 billion light years in radius. I get
about 20 milliwatts per square meter. What accounts for the factor
of two discrepancy? Probably polarization. LIGO, if I understand
correctly, is sensitive to only one of the two polarizations.


Also, red shift. 200 solar masses per second at the event equals
about 180 solar masses per second on Earth, as the event is receding
from us at about a tenth of the speed of light. Also, the received
frequency at the time of peak power, about 250 Hz, was originally
about 270 Hz. That's an impressive orbital period (1/270 second)
for two 30-solar-mass objects.

The last column is the number of gravitons per square meter per
second. I get that by multiplying the flux by the frequency and
dividing by Plank's constant.


Sigh. Of course I should have *divided* by the frequency, not
multiplied. So my estimated numbers of of gravitons were about five
orders of magnitude too high.

The total number of gravitons emitted by the event was about 3E+78.

I hope someone checks my math.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

  #14  
Old February 16th 16, 08:48 PM posted to sci.astro.research, ci.physics.research
Steve Willner
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Posts: 1,172
Default Advanced LIGO has detected gravitational waves from a binary black hole collision/merger

In article ,
Jos Bergervoet writes:
Why are the 2 predicted curve in this picture slightly different?
https://www.ligo.caltech.edu/image/ligo20160211a


As the caption notes, one of the curves has to be inverted and
shifted by 7 ms because of the different detector locations and
orientations. The rest of the differences are presumably random
noise. The signal to noise is only 5 sigma, after all. Figure 1 of
the published paper is clearer.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

  #15  
Old February 16th 16, 10:17 PM posted to sci.physics.research,sci.astro.research
Gregor Scholten
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Posts: 3
Default Advanced LIGO has detected gravitational waves from a binary

Nicolaas Vroom 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.


What I'm asking myself is:
Consider a sphere of 1.3 billion light years (as a matter of thought)
around our Sun.
Than nowhere at this sphere 1.3 billion years ago a similar event
i.e. inspiral and merger BH, took place.
Because if it did we would see both.
Also nowhere at the path, during its travel time of the wave,
from the origin of the event to the moment (point) of detection,
a similar event took place. Because if it did etc.
Assume that this path is a straight line.


It seems to me that you do not clearly distinguish between the path in
space and the path in spacetime. If we consider the path in space,
numerous similar events could have taken place without being detectable
for us today, because the emitted gravitational waves would have already
passed us a long time ago.

Than also starting from any point on the sphere mentioned above,
in a straight line to the point of detection a similar event
took place. Because if it did etc.

What I want to point out is to detect solely only one inspiral BH is
quite remarkable. What I would expect is that there would be more
binary BH's mergers in progress. Apparently this is not the case.


Your conclusion is wrong. There could be many mergergs being in
progress. But the gravitational waves did not reach us yet, but may do
so in e.g. 1 year, or 10 years, or 1000 years.

Consider supernovae for comparison. Assume we observe a single supernova
now. That does not mean that there were no other supernovae ongoing. The
matter of fact is simply that the light of other supernovae does not
reach us now, but may reach us in 1 year, or 10 years, or 1000 years.

  #16  
Old February 18th 16, 09:20 AM posted to sci.astro.research,sci.physics.research
Jos Bergervoet
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Posts: 126
Default Advanced LIGO has detected gravitational waves from a binaryblack hole collision/merger

On 2/16/2016 8:48 PM, Steve Willner wrote:
In article ,
Jos Bergervoet writes:
Why are the 2 predicted curve in this picture slightly different?
https://www.ligo.caltech.edu/image/ligo20160211a


As the caption notes, one of the curves has to be inverted and
shifted by 7 ms because of the different detector locations and
orientations.


The data are shifted, not the predicted curves, those are
inverted but not shifted as can clearly be seen in the
ring-down region at the end.

The rest of the differences are presumably random
noise.


There will be noise in the data, but why in the predictions?

The signal to noise is only 5 sigma, after all. Figure 1 of
the published paper is clearer.


OK, we look at:
https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_Detection_of_GW150914.pdf

There in Fig. 1, the predicted curves are called "Numerical
relativity" and they *still* have differences in shape, that
are not inversion or shift transformations! It is becoming
more and more intriguing.

Possible explanations:
1) For some reason (to make the curve look more "natural"?)
someone decided to add random noise to the computed results.
And they added *different* noise for Hanford and Livingston.
To me this seems a silly eplanation.
2) The results are different polarization componentsa (after
all you only need a 45 degree tilt to see the independent
other polarization for a spin-2 field.)
3) The numerical routines generate some numerical errors
visible as small random looking "ripples" in the computed
result. This seems likely since complex curved space-time
will enforce a complicated non-uniform grid in the 4
coordinates.

A combination of 2) and 3) seems most likely to me (I didn't
find any proof for it in the text, but I may have overlooked
it in the extensive list of papers that have accumulated.)

--
Jos








  #17  
Old February 18th 16, 02:52 PM posted to sci.astro.research,sci.physics.research
Hendrik van Hees
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Posts: 1
Default Advanced LIGO has detected gravitational waves from a binary black hole collision/merger

On 18/02/16 09:20, Jos Bergervoet wrote:
OK, we look at:
https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_Detection_of_GW150914.pdf

There in Fig. 1, the predicted curves are called "Numerical
relativity" and they *still* have differences in shape, that
are not inversion or shift transformations! It is becoming
more and more intriguing.

Possible explanations:
1) For some reason (to make the curve look more "natural"?)
someone decided to add random noise to the computed results.
And they added *different* noise for Hanford and Livingston.
To me this seems a silly eplanation.
2) The results are different polarization componentsa (after
all you only need a 45 degree tilt to see the independent
other polarization for a spin-2 field.)
3) The numerical routines generate some numerical errors
visible as small random looking "ripples" in the computed
result. This seems likely since complex curved space-time
will enforce a complicated non-uniform grid in the 4
coordinates.

A combination of 2) and 3) seems most likely to me (I didn't
find any proof for it in the text, but I may have overlooked
it in the extensive list of papers that have accumulated.)


As far as I understand as a non-expert in the field of GWs, in the PRL
they write that the numerical-relativity and the sine-Gauss wavelet fits
are ploted within the "detector filter". That's the usual way to compare
calculations with data. Also in our field (relativistic heavy-ion
collisions) you have to run your theoretical results for cross sections
and related observables through the detector-acceptance filter.
Sometimes that's a simple cut but often it's also a numerical routine
developed by the experimentalists taking into account details of the
detector. I guess, that's the same here. The analysis of the GW signals
out of the detector noise is far from trivial, and I cannot understand
this in all details, of course. Note that there are a lot of papers by
the LIGO+VIRGO collaboration on the arXiv, where you can find many more
details. Among them are some papers about the analysis of the detector
noise and GW signal reconstruction:

http://arxiv.org/abs/1602.03843
http://arxiv.org/abs/1602.03845
http://arxiv.org/abs/1602.03844

--
Hendrik van Hees
Goethe University (Institute for Theoretical Physics)
D-60438 Frankfurt am Main
http://fias.uni-frankfurt.de/~hees/

[Mod. note: quoted text trimmed --mjh]
  #18  
Old February 18th 16, 02:57 PM posted to sci.astro.research
Nicolaas Vroom
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Posts: 216
Default Advanced LIGO has detected gravitational waves from a binary

Op dinsdag 16 februari 2016 22:17:56 UTC+1 schreef Gregor Scholten:
It seems to me that you do not clearly distinguish between the path in
space and the path in spacetime. If we consider the path in space,
numerous similar events could have taken place without being detectable
for us today, because the emitted gravitational waves would have already
passed us a long time ago.


Consider an event (BH merger) at a certain distance r0 from an observer
at a moment t0. The gravitional waves propagates towards observer.
At t1 this wave is at a distance r1 at t2 at a distance r2 and at
t10 at a distance r10 = 0 i.e. the wave reaches the Observer.
In this case I divide the path in 10 steps but you can also consider
100 steps i.e. any number.

The point is if at any of these positions (tn,rn) also a second
independent BH merger takes place than at (t10,r10=0) the observer
will receive a super position of two gravitational waves. And that
is not what we want (?)

The next thing you can do is draw a sphere with radius r0 around
Observer. If at t0 at this whole sphere there is also a BH merger than
the gravitational waves from that event will also reach the observer
at (t10,r10=0). Again a superposition and that is not what we want.
It should be mentioned that the concept of a sphere with radius r0
is an approximation.

The same thing you can do for all the rn at tn. At each of the spheres
rn at tn there should not be any second BH merger in progress,
because if it does you will receive sets at t10,r10=0.

To get a different idea about of what I see as a problem: suppose
gravity waves act instantaneous. This means that at this instant
if you observe 1 BH merger, there should not be any second BH merger in
progress at a radius of roughly 2 billion light years,


Consider supernovae for comparison. Assume we observe a single supernova
now. That does not mean that there were no other supernovae ongoing. The
matter of fact is simply that the light of other supernovae does not
reach us now, but may reach us in 1 year, or 10 years, or 1000 years.


To detect a single supernova the story is different. At each instant
you can detect many supernovae simultaneous assuming their directions
come from different positions on the sphere surrounding us.

Nicolaas Vroom
  #19  
Old February 18th 16, 09:27 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default Advanced LIGO has detected gravitational waves from a binary

In article , Nicolaas Vroom
writes:

Consider an event (BH merger) at a certain distance r0 from an observer
at a moment t0. The gravitional waves propagates towards observer.
At t1 this wave is at a distance r1 at t2 at a distance r2 and at
t10 at a distance r10 = 0 i.e. the wave reaches the Observer.
In this case I divide the path in 10 steps but you can also consider
100 steps i.e. any number.

The point is if at any of these positions (tn,rn) also a second
independent BH merger takes place than at (t10,r10=0) the observer
will receive a super position of two gravitational waves. And that
is not what we want (?)

The next thing you can do is draw a sphere with radius r0 around
Observer. If at t0 at this whole sphere there is also a BH merger than
the gravitational waves from that event will also reach the observer
at (t10,r10=0). Again a superposition and that is not what we want.
It should be mentioned that the concept of a sphere with radius r0
is an approximation.


OK. Consider that such an event lasts a few seconds or whatever. One
can get some idea about the chances of two or more overlapping (the one
at the farther distance taking place farther in the past, of course).
People have done the calculations and estimates of the numbers of such
events. I don't think "confusion", as this is probably called, that is,
more than one event observable at the same time, is an issue here.

To get a different idea about of what I see as a problem: suppose
gravity waves act instantaneous. This means that at this instant
if you observe 1 BH merger, there should not be any second BH merger in
progress at a radius of roughly 2 billion light years,


But they travel at the speed of light. If not, GR is incorrect, then
you can't trust the rest of your calculations either. IIRC one could
detect the time-of-arrival distance between the two detectors.

Consider supernovae for comparison. Assume we observe a single supernova
now. That does not mean that there were no other supernovae ongoing. The
matter of fact is simply that the light of other supernovae does not
reach us now, but may reach us in 1 year, or 10 years, or 1000 years.


Same with gravitational-wave events.

To detect a single supernova the story is different. At each instant
you can detect many supernovae simultaneous assuming their directions
come from different positions on the sphere surrounding us.


In principle the same with gravitational waves. However, since they
last much shorter than a supernova, probably only one is visible at any
given time.
  #20  
Old February 19th 16, 08:14 AM posted to sci.astro.research,sci.physics.research
Daniel S. Riley
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Posts: 4
Default Advanced LIGO has detected gravitational waves from a binary black hole collision/merger

Jos Bergervoet writes:
OK, we look at:
https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914_Detection_of_GW150914.pdf

There in Fig. 1, the predicted curves are called "Numerical
relativity" and they *still* have differences in shape, that
are not inversion or shift transformations! It is becoming
more and more intriguing.

Possible explanations:
1) For some reason (to make the curve look more "natural"?)
someone decided to add random noise to the computed results.
And they added *different* noise for Hanford and Livingston.
To me this seems a silly eplanation.


The numerical relativity curves are "projected onto each detector",
which I'd assume means they started with a theoretical prediction and
then projected it onto the detector response--that's what one does for
comparison with an observed signal. So look at figure 3(b) of that
paper, and you'll see that the two sites have some significant
differences in instrument noise. They may have simulated the noise
and the band-reject filters, or just the filters, it probably says in
one of the papers I haven't looked at yet. But either way is going
to result in small differences in the theoretical expectations for
the two instruments.

-dan
 




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