A Rumors of Gravitational Wave Inspiral at Advanced LIGO | Sept 2015 Launch

  • #51
mfb said:
The gravitational potential energy got converted to gravitational waves, that is exactly the point.
I was asking about the negative energy due to the holes being near each other as opposed to at infinity. I would expect this to decrease the gravitational wave energy output, as compared with a simple comparison of the masses.
mfb said:
That is negligible.
Why? Both holes attain near-light speeds, so shouldn't the kinetic energy be comparable to, or even several times, the mass energy?
mfb said:
Rotational energy of the final black hole is part of its total energy, so it is part of its mass.
I thought the quoted masses referred to Lorentz-invariant rest mass. Rotational energy is frame-dependent, so shouldn't it be accounted for separately?
 
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  • #52
maline said:
I was asking about the negative energy due to the holes being near each other as opposed to at infinity. I would expect this to decrease the gravitational wave energy output, as compared with a simple comparison of the masses.
It is the source of the gravitational wave output, in terms of energy balance.
maline said:
Why? Both holes attain near-light speeds, so shouldn't the kinetic energy be comparable to, or even several times, the mass energy?
The initial kinetic energy is negligible. Later it increases, but only by (approximately) half the value the reducing gravitational potential energy sets free.
maline said:
I thought the quoted masses referred to Lorentz-invariant rest mass. Rotational energy is frame-dependent, so shouldn't it be accounted for separately?
All numbers are as seen by an observer far away. The black hole mass is determined by the total energy.
 
  • #53
mfb said:
All numbers are as seen by an observer far away. The black hole mass is determined by the total energy.
So the numbers given include the kinetic & gravitational "potential" contributions as well?
And these "masses" decrease steadily as the waves are emitted, with the change mainly in the increasingly negative gravitational component which is only partially compensated by the increasing kinetic energy?
Meanwhile, the two invariant masses remain more or less constant?
And in the actual merger, the final invariant mass is actually perhaps 4 SM's less than the sum of original invariant masses, but there is also perhaps 1 SM of rotational energy, leaving the net loss at 3 SM's?
Let me know if I got it! Thanks!
 
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  • #55
martinbn said:
There's this

I can't wait for this announcement. I keep staring at the video in post #45 waiting for the press conference to begin. It's not so bad, actually, at least I can monitor the Cosmic Microwave Background while I'm waiting..
 
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  • #56
phyzguy said:
There is a rumor going around that a gravitational wave inspiral has been seen at advanced LIGO. The web sites say it went on line in Sept, 2015, so I guess this is possible. Has anyone here heard anything?

I heard there was going to be a news conference announcing the discovery/detection of gravitational ways today (Thursday 11th February) ... ... has anyone got any news on this ...?
 
  • #58
Thanks for that ... Peter
 
  • #60
ujjwal3097 said:
can we watch the whole conference on the nature site

It's not clear, but I think so.
 
  • #61
e.bar.goum said:
It's not clear, but I think so.
yes! you are right because there is no info about the video. Site just says if you want to set the reminder.
 
  • #62
Not long to go now... Here's a link to the youtube live feed:

 
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  • #63
Daz said:
Not long to go now... Here's a link to the youtube live feed:


thanks so much

I hope for something good
 
  • #64
So to summarise, LIGO has detected a gravitational wave signal from a black hole merger which occurred over a billion years ago. The signal was seen independently by the two detectors with perfect coincidence. The event radiated a total of 3 solar masses in gravitational waves.
 
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  • #65
Here's the signal:

ligo_signals_overlaid.jpg


The PRL paper is supposed to be available online at this time. Right now the PRL website appears to be overloaded and not responding :-)
 
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  • #66
bcrowell said:
Here's the signal:
Note the unit of strain on the y-axis. That is an incredibly small number. To detect that is truly amazing.
 
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  • #67
A few quick notes from the press conference:

2 colliding back holes
1.3 10^9 ly
2015 sep 14
freq increasing with time, as expected for inspiraling black holes
8:00 animation of inspiraling black holes
each 150 km diam
~30 Msun, v significant fraction of c
9:30 animation with grav waves
stretch is 1/1000 diameter of proton
12:00 big risk for NSF to fund it
15:30 signal obviously visible
16:20 seen obviously by eye
curve fitting gives initial masses, mass loss, and distance
20:00 chirp played as audio (with frequency shift)
 
  • #69
I really enjoyed Rainer Weiss' explanation, let's hope the press has been paying attention.
 
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  • #70
Abstract of the paper:

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10−21. It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203 000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410+160−180Mpc corresponding to a redshift z=0.09+0.03−0.04. In the source frame, the initial black hole masses are 36+5−4M⊙ and 29+4−4M⊙, and the final black hole mass is 62+4−4M⊙, with 3.0+0.5−0.5M⊙c2 radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

The paper appears to be under a CC license and not paywalled. Currently attempting to download it.
 
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  • #72
Kip Thorne is speaking now. He says the peak power was 50 times greater than the total power output of all the stars in the [observable] universe.

The rumors on the internet were saying there were several events, but at the press conference they're only discussing one. I wonder if the paper will discuss the other events, or if they weren't really statistically significant enough to be publishable.

It's surprising that the signal from the best event is so clearly visible on a time-domain graph, if, as rumored, it was only 5 sigma over all.
 
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  • #73
bcrowell said:
Right now the PRL website appears to be overloaded and not responding
Could the majority of the traffic be due to this gravitational wave discovery?
 
  • #74
Since it's CC licensed, it's legal to download and repost it on the internet. If anyone can coax a copy out of their overloaded server and do that, that would be great. I'm still trying and not having much luck.
 
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  • #75
Q&A:

One of the things they checked to make sure that it was a real signal was to look at all the data channels for every part of the experiment (servos, etc.), and make sure that none of them was similar to the putative signal.

This version of LIGO is about 3x more sensitive than the previous version. They will tweak the apparatus soon to make it more sensitive by an additional factor of about 3x. The paper will have a statistical analysis of what kind of event rates they expect to see, based on the number of signals they've seen so far in the time it's been operating. The current version is also sensitive to lower frequencies than before.

The concept was first proposed by Russians in 1962.

Unfortunate political compromises, politics of funding. US has not been funding LISA. LISA has released test masses as a test.
 
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  • #76
Phys Rev Lett. Are tweeting snippets of the paper "until their servers are back online." (Obviously overloaded by us lot trying to get a peek!)

https://twitter.com/PhysRevLett
 
  • #77
bcrowell said:
It's surprising that the signal from the best event is so clearly visible on a time-domain graph, if, as rumored, it was only 5 sigma over all.
In the CERN seminar this was explained in more detail. They ran for 16 days (of coincidence time between the two detectors) and used this background data to estimate how often stronger signals occur. Their estimate is less than once in ~200.000 years (forgot the second digit). Compare that to 16 days of running time...
The signal is probably more significant, but they would have needed more time for a better background estimate to claim a higher significance.

If the license allows (!) and if someone manages to download the paper, it would be nice to upload it here to help distribution.
 
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  • #80
mfb said:
In the CERN seminar this was explained in more detail. They ran for 16 days (of coincidence time between the two detectors) and used this background data to estimate how often stronger signals occur. Their estimate is less than once in ~200.000 years (forgot the second digit). Compare that to 16 days of running time...

The abstract says "a false alarm rate estimated to be less than 1 event per 203 000 years", not the event rate. I saw somewhere that the expected event rate was between 0.5 and several hundred events per year.
 
  • #81
What major questions of fundamental physics will these Gravity Wave observations help to resolve, and how?

What major questions of astronomy will Gravity Wave observations help to explain?
 
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  • #82
An amazing announcement. I was reading all about these gravitation waves in Brian Greene's books the past few months. Really hits home for me after reading about it.
 
  • #84
Will Gravitational Wave Astronomy help us to verify Dark Matter?

Would it be possible for Gravitational Astronomy to differentiate between Dark Matter and regular matter - perhaps by cross-referencing with other forms of astronomical observation?
 
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  • #86
Great news-big day for science!
I know its still early, but can someone say which theories are hurt, (and which ones are favored) the most by these new findings?
 
  • #87
Was there a corresponding gamma ray burst?

Aren't events that produce gravitational waves (collisions of black holes and neutron stars) also supposed to produce GRBs?
 
  • #88
mjs said:
Great news-big day for science!
I know its still early, but can someone say which theories are hurt, (and which ones are favored) the most by these new findings?

Simple answer is that Einsteinian GR seems to describe the event to near perfection. The paper from LIGO says, "The agreement between the reconstructed waveforms using the two models is found to 94(+2;-3) %". This is the most stringent test yet of GR in the strong gravity regime. I'm not sure if this kills some alternatives to GR, but I think it will disfavor some of them.
 
  • #89
phyzguy said:
Simple answer is that Einsteinian GR seems to describe the event to near perfection. The paper from LIGO says, "The agreement between the reconstructed waveforms using the two models is found to 94(+2;-3) %". This is the most stringent test yet of GR in the strong gravity regime. I'm not sure if this kills some alternatives to GR, but I think it will disfavor some of them.
There is a class of quantum gravity approaches (based on a variant way of handling spin 2 quantization, put forward by a few Russian physicists), that had a specific prediction (yeah!) that collapse would stop signficantly before horizon formation (as I recall, close to the photon sphere of classical GR). Presumably this result (along with increasing reliability of horizon / mass observations) completely kills this approach (the downside of a specific prediction). It probably kills most any approache that suggests the QG effects diverge from classical GR outside the horizon.
 
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  • #90
JorisL said:
I really enjoyed Rainer Weiss' explanation, let's hope the press has been paying attention.

Rainer Weiss was one of my experimental physics teachers. I loved his class. I always remember his story about dropping out of MIT. And of course, that he was one of those trying to do this crazy experiment near the quantum limit :)
 
  • #91
PAllen said:
It probably kills most any approache that suggests the QG effects diverge from classical GR outside the horizon.
Interesting point. My understanding is that the people saying this kind of thing were working within semiclassical gravity, and they had to renormalize the results of their calculations. It seems to me that once you give yourself the power to arbitrarily renormalize away any effect you feel like getting rid of, you immunize your theory against this kind of straightforward falsification by observation. If they had previously predicted some big effect at or outside the event horizon, now they can probably just say, "Oh, we'll make that go away by subtracting out a certain term from our equations."
 
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  • #92
bcrowell said:
Interesting point. My understanding is that the people saying this kind of thing were working within semiclassical gravity, and they had to renormalize the results of their calculations. It seems to me that once you give yourself the power to arbitrarily renormalize away any effect you feel like getting rid of, you immunize your theory against this kind of straightforward falsification by observation. If they had previously predicted some big effect at or outside the event horizon, now they can probably just say, "Oh, we'll make that go away by subtracting out a certain term from our equations."
Yes, but if the claim to distinction of such approach was what it said outside the horizon, it loses that. Unless it has some other point of interest, even its authors might not bother with it anymore.
 
  • #93
Curious if there are other highly sensitive experiments that see an effect from this event. (Such as gama ray detectors or dark matter searches) It would be interesting to take the know arrival time and look for blips in the data...
Or is this effect so weak as to make this search pointless?
 
  • #95
Orodruin said:
The event radiated a total of 3 solar masses in gravitational waves.
What portion of the universe's mass is in the form of gravitational waves?
 
  • #96
.Scott said:
What portion of the universe's mass is in the form of gravitational waves?

Almost none, and we don't know why. A maximum-entropy big bang, which is the most overwhelmingly likely possibility, would have had its gravitational degrees of freedom equilibrated with all the other degrees of freedom, so primordial gravitational waves would have been extremely strong. Instead, we got a big bang that was low in entropy, mainly because of the almost complete lack of gravitational waves.
 
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  • #97
That's why I said background ("and used this background data to estimate how often stronger signals occur [by background fluctuations]").
The event rate is poorly constrained with a single signal, of course, but we'll know more in a year or once more events are available (whatever happens faster).

Let's see if LISA gets more funding now. The science case certainly got stronger.

.Scott said:
What portion of the universe's mass is in the form of gravitational waves?
Cosmic energy inventory
About 30 part in a billion, with a large uncertainty (~factor 3).
 
  • #98
I noticed some odd inconsistencies between among several reports. (Bolding mine.)

From http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102
On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave
Observatory simultaneously observed a transient gravitational-wave signal​

From https://en.wikipedia.org/wiki/LIGO#Advanced_LIGO
On September 18, 2015, Advanced LIGO began its first formal science observations at about four times the sensitivity of the initial LIGO interferometers.
​
From https://www.ligo.caltech.edu/news/ligo20150918
On, Friday, September 18th 2015, the first official 'observing run' (O1) of LIGO's advanced detectors in Hanford WA and Livingston LA quietly began when the clock struck 8 a.m.​

I looked on the internet for earlier dates than September 18th for when the advanced LIGO began its search for gravitational waves, but that was the earliest date I could find. It seems that the discovery took place four days before the "official" search began.
 
  • #99
Buzz Bloom said:
It seems that the discovery took place four days before the search began.

This was discussed at the press conference. They were doing an engineering run, which wasn't supposed to be a physics run. However, the apparatus was functioning as it needed to be in order to detect a real signal, and that happened to be when they got this signal.
 
  • #100
Ahah, nice interpretation of the picture.

Yes, they have claimed today they have indeed observed gravitational waves from one event 1.3 billion light years away. The wave form they recorded matches the theoretical prediction, with increasing amplitude and frequency up to a peak, after which it settles down to a more stable configuration. This is indeed what is expected in the event of two black holes orbiting each other at ever decreasing distance, until they merge.

I have a question, which was partially discussed in other places on the web, for anyone to comment on: can gravitational waves be red-shifted?

It seems they can, as they travel against a gravitational potential, from a region of high gravitational field (low potential) to one with lower gravitational field (higher potential). In particular, as electromagnetic radiation, the rate at which time passes as they travel through the potential increases, thus their frequency decreases.

However, as they travel, they also distort time, so I am wondering if in any case these two effects influence each other.

Does anyone have any insight on this?

Thanks!
 
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