Observation of Gravitational Waves from a Binary Black Hole Merger

[gary]

To gain some feel for how quickly the merger took place, the supercomputer
simulation animation given at the press conference may help be of
assistance to some readers.

Start at 33:50
https://www.youtube.com/watch?v=vy5vDtviIz0

The final merger takes 20ms.

However, as addressed in an answer to a question in the video
(go to 56:47) that last 20ms represents the signal from the final merger
when the signal rose above the noise floor of the instruments.

Long before that, as the black holes orbited each other, there would
have still been a fainter gravitational signal.

Frans Pretorius of Princeton specializes in numerical solutions of
the field equations for general relativity and came up with
the first supercomputer solution of two black holes merging only
relatively recently, in 2005.

See http://arxiv.org/pdf/gr-qc/0507014v1.pdf

He was awarded the 2010 Aneesur Rahman Prize for Computational Physics
for this brilliant work.

See https://www.aps.org/programs/honors/...rius&year=2010

Shortly after the Pretorius breakthrough in 2005, a different numerical
approach was discovered and groups have been improving the accuracy of simulations ever since.

See http://w.astro.berkeley.edu/~gmarcy/...le_mergers.pdf

These simulations were able to provide the gravitational wave community
with waveform signatures to look for.

2013 talk by Frans Pretorius on YouTube -
https://www.youtube.com/watch?v=UtzJIkg3ZpM

The sound quality is poor but Pretorius discusses black hole mergers at 28:24.

"When Black Holes Collide" presentation here in PDF format -
http://www.stsci.edu/institute/itsd/...retorius021809

There are three phases to a merger - inspiral merger & ringdown.
See http://arxiv.org/abs/1102.3781

The ringdown period was predicted by the models to be damped.
See http://arxiv.org/pdf/1102.3781v1.pdf

[xelasnave]

Thank you Steven.

[xelasnave]

Thank you Gary

[Amaranthus (Barry)]

During the 20ms of the merger, this event released roughly 50 times more energy than the totality of rest of the stars in the observable UNIVERSE: 3.6 x 10^49 joules/sec (200 solar masses converted to pure energy).
http://www.techinsider.io/black-hole...niverse-2016-2

Contemplate that!

[silv (Annette)]

Thank you Steven, and thank you, Gary for the URL collection and explanations!

[Steffen]

Originally Posted by silv

Shiraz,
I guess there is a reason for peer reviewed papers, eh?
And also a reason for papers without such quality control :p

I suppose this discovery was well-vetted before publication. I think Lawrence Krauss may have blabbed about it on Twitter a month ago, then retracted it as a rumour

[silv (Annette)]

ah, no, Shiraz had linked to an article of a different kind and I'm referring to that one.

did you all read the one on TheConversation? by members of the Australian teams? I liked it over brekkie. Not scientific.
https://theconversation.com/australi...al-waves-54525

[Eratosthenes (Peter)]

Originally Posted by Amaranthus

During the 20ms of the merger, this event released roughly 50 times more energy than the totality of rest of the stars in the observable UNIVERSE: 3.6 x 10^49 joules/sec (200 solar masses converted to pure energy).
http://www.techinsider.io/black-hole...niverse-2016-2

Contemplate that!

the energy involved reflects the fact that the space-time continuum has been disturbed and measured across a vast distance, albeit a short and faint signal.

the flip side of this is that perhaps these massive energy and collision events arent very common.

I wonder if they will detect something similar in the future?

[deanm (Dean)]

Why was the signal so brief?

As indicated by sjastro, the most intense GW radiation takes place just before the 'merge' - 2 black holes, each around 30 solar masses, rotating about a common centre of mass, 10s of times per second, just before coalescing.

Immediately before & after, the signal is simply not detectable with our current technology.

In the future, we'll be able to detect many of these ultra-energetic, cataclysmic events using multiple GW 'observatories' around the globe.

That will allow ever-more precise triangulation & current predictions are that we'll identify optical correlations.

This is just the beginning....Wow!

Dean

[silv (Annette)]

yes, in the press conference video Gary provided a link to, I think the bright-eyed, passionate lady answered this question from the audience in the Q&A.

Such a pitty, Q&A was cut short in the video! Does anyone know of a longer version?

[silv (Annette)]

I was brooding about the question what was really measured when the spikey pattern occurred.

From what I understood, the measurement describes the amount of the 2 laser beams became out of sync and therefor hit the end mirror at different times than the 0-signal-calibration was set to.

So the time had changed it took the beams to travel the given distance , right?
It was not the distance that changed, only the time it took.
That's important to differentiate, I think, because a friend of mine, also a lay person, and also only IT-educated, imagines that the (3-dimensional) space in the tube had been squished and stretched by the GW causing the beam to have to travel, say, 2 cm more than usual.

But it was the time, only the time.
Just like with the atomic clock ticking slower on Earth, right in the trough of the space-time-liquid/fabric, than up in the air on a plane.

Is that correct?

So if this is right, then this also applies to all "light signals" from distant sources: they are affected by all the random GW which were caused by incidents since the dawn of time.

And that means, the light we observe has not travelled at the same "speed" all the way to us.
It often "surfed", meandered on gravitational waves which caused the light to take longer and shorter to get from A to B.

(The absolute speed itself did not change, okay. But the relative speed did.)

And what might this uncertainty implicate?

Maybe, the light we observe is not as old as we thought it is. Because of a huge amount of incidents with GW radiating through the light's path.

Is an observed redshift red-er because the light encountered a few more GW?

If this is so -
and, at the time we on Earth observe the light beams coming in from different directions of the universe,
they will have encountered different GW tides.
then we are looking at "unclean" environments and the calculations we made based on the assumption that the speed of light is a constant, are wrong.

[sjastro]

The interference pattern is in fact caused by a change of distance between the mirrors hence the time of travel of the split laser beam is different.
The speed of light remains unchanged.

A passing gravitational wave gives space a quadrupole or "squashed sphere" symmetry composed of a short and long axis.
When a gravitational wave passes transversely through a distribution of masses in space the quadrupole symmetry results in either pulling the masses apart or pushing them closer together, depending on the orientation of the wave to the masses.
https://en.wikipedia.org/wiki/File:G...larization.gif

The LIGO interferometer is based on the same principle. The mirror distance orientated in a longitudinal direction to the wave remains unchanged but in the transverse orientation, the mirror distance will change due to the quadrupole symmetry of the wave. Hence the differences in the longitudinal and transverse mirrors distances will be detected as an interference pattern.

[gary]

Originally Posted by silv

That's important to differentiate, I think, because a friend of mine, also a lay person, and also only IT-educated, imagines that the (3-dimensional) space in the tube had been squished and stretched by the GW causing the beam to have to travel, say, 2 cm more than usual.

Hi Sliv,

To provide some sense of how miniscule the changes in distance being
measured are, LIGO can resolve down to 1/1000th the diameter
of a proton, or some 1 x 10-18 meters.

That is 0.00000000000000001 meters.

If you drew a line between the Sun and the next nearest star some 4 light
years away, LIGO could detect the change in distance down to the thickness of
a human hair.

[silv (Annette)]

Thank you reading and replying

What I struggle with is:
are these metaphors used to accommodate the audience's 3-dimensional thinking?

is this only a metaphor:
stating that the mirror moved on its suspension ropes - (let's disregard whether by a fraction of the size of a proton or by 2 cm) - or stating that the actual tubes became longer and shorter.

Or was it in actual fact a change measured in the suspension rope (or whatever it looks like in the Ligo, if it's not a real rope).

Or was it in actual fact the length of the tube that got measured? By holding a ruler at it?


Well, I understood those explanations as metaphors.

And I assume, what got in fact measured was the time difference by which the split beams arrived at their common target.

So the light beams got affected by the GW. Time got affected.

And not the stationary objects like mirrors and tubes.

I think here is really my problem: not knowing when scientists speak in metaphors to make it easier to understand - or when they actually speak "autistically exact".

[Bill.davey (Bill)]

My simplistic understanding is this.
Gravity waves affect the fabric of space-time. The Gw's lengthened and shortened the tubes, the ground around the tubes, the people, everything. As everything physical is affected nothing physical can be used to measure this change in length.
The one constant in the known universe is the speed of light in a vacuum. It is not affected by gravity waves. Therefore the light was used to measure the change in length of the tubes. Tubes at right angles to each other so that they are affected differently by the GW's passing.

[sjastro]

Silv,

No metaphors are being used as the descriptions are of real events.

General Relativity is counterintuitive because it appears to contradict our understanding of measuring distances.
If the distance between two points changes the logical assumption is to claim one or both points has moved to a different position in space.
Alternatively and far less intuitive is that the two points have not moved but the space between the points has changed.
In this scenario we cannot perceive nor measure the change as a ruler is also affected by the change.

Light however has an interesting property, it will always travel along a null geodesic path. In other words it will always travel along the shortest pathway between two points in space. In flat space this is a straight line, in spherical space along an arc etc.

When a gravitational wave passes through an interferometer the position of the mirrors remain in the same spatial position hence their ruler distance doesn't change.
The geometry of the distorted space between the mirrors is different in the longitudinal and transverse directions.

Light travelling in the longitudinal direction of the wave is on a different geodesic to light travelling in the transverse direction. In the transverse direction the space contracts and expands due to the quadrupole symmetry of the wave. (Expansion occurs perpendicularly to the direction of contraction.)

As a result the two beams will be out of phase and an interference pattern is observed.

Regards

Steven

[Eratosthenes (Peter)]

the source of the disturbance is non linear and dynamic in nature, and so a "pulse-type" signal is generated.

it is was foreseen in scripture

The great Priest Kip Thorn knew what was coming as far back as the late 1970s......he knew that a LIGO type detector would be built...

He knew that the heavens would open up in rapture

Today we must celebrate the great spiritual achievements of this great global religion - SCIENCE

[Shiraz (Ray)]

fwiw, the sounds of a few different classes of merger events are here - from 2004, so these are fairly old predictions. http://web.mit.edu/sahughes/www/sounds.html

more up to date stuff with discussion here, but not as easily accessible http://gmunu.mit.edu/sounds/comparab...le_sounds.html

the mergers with a galaxy-class black hole are wild.

[sjastro]

Originally Posted by Eratosthenes

the source of the disturbance is non linear and dynamic in nature, and so a "pulse-type" signal is generated.

it is was foreseen in scripture

The great Priest Kip Thorn knew what was coming as far back as the late 1970s......he knew that a LIGO type detector would be built...

He knew that the heavens would open up in rapture

Today we must celebrate the great spiritual achievements of this great global religion - SCIENCE

Don't let the facts get in the way of a good story.
https://en.wikipedia.org/wiki/Joseph_Weber

[torsion (Bram)]

It is an amazing discovery 30-40 years in the making!

Steven in post 36 explains it right.

Some more info:

A nice visual explanation is given here: http://www.phdcomics.com/comics.php?f=1853

A nice public/outreach science summary can be found here: https://www.ligo.caltech.edu/system/...ce-summary.pdf

An overview of the Australian contribution can be found here: http://www.aciga.org.au/news/australian-contribution

A nice visual and audible youtube clip of the actual event is here: https://www.youtube.com/watch?v=egfB...ature=youtu.be

More detailed information (and photos/figures) can be found here: https://www.ligo.caltech.edu/detection

cheers,
Bram