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

[ujjwal3097]

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.

 

[Daz]

Not long to go now... Here's a link to the youtube live feed:

 

[ujjwal3097]

Not long to go now... Here's a link to the youtube live feed:

thanks so much

I hope for something good

 

[Orodruin]

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.

 

[bcrowell]

Here's the signal:

The PRL paper is supposed to be available online at this time. Right now the PRL website appears to be overloaded and not responding :-)

 

[Orodruin]

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.

 

[bcrowell]

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)

 

[bcrowell]

This seems to be the URL of the paper:

abstract: http://link.aps.org/doi/10.1103/PhysRevLett.116.061102

pdf: http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102

The site is overloaded, so I can't tell yet whether the paper is paywalled.

Op ed piece on the Physical Review site: http://physics.aps.org/articles/v9/17

 

[JorisL]

I really enjoyed Rainer Weiss' explanation, let's hope the press has been paying attention.

 

[bcrowell]

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.

 

[jedishrfu]

Gravity Wave have reached our shores:

http://www.sciencemag.org/news/2016...nstein-s-ripples-spacetime-spotted-first-time

 

[bcrowell]

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.

 

[maNoFchangE]

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?

 

[bcrowell]

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.

 

[bcrowell]

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.

 

[Daz]

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

 

[mfb]

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.

 

[websterling]

Looks like the papers are available from LIGO-

https://dcc.ligo.org/LIGO-P150914/public

 

[levadny]

Looks like the papers are available from LIGO-

https://dcc.ligo.org/LIGO-P150914/public

Thanks a lot! I translate in Russian this article.

 

[websterling]

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.

 

[sanman]

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?

 

[RJLiberator]

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.

 

[fresh_42]

The original publication on gravitational waves.

 

[sanman]

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?

 

[RJLiberator]

Great read on the situation: http://www.slate.com/blogs/bad_astr...itational_waves_finally_detected_at_ligo.html

 

[mjs]

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?

 

[cockpitvisit]

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?

 

[phyzguy]

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.

 

[PAllen]

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.

 

[atyy]

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 :)