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

[lpetrich]

So to get from 400 megaparsecs to 4 kiloparsecs means increasing the amplitude by a factor of 10⁵, up to 10^-16.

 

[PAllen]

So to get from 400 megaparsecs to 4 kiloparsecs means increasing the amplitude by a factor of 10⁵, up to 10^-16.

How do you get that? Wave amplitide goes a 1/r. Power passing through a given surface area goes as 1/r².

 

[Jorrie]

How do you get that? Wave amplitide goes a 1/r. Power passing through a given surface area goes as 1/r².

It looks correct to me - the ratio 400 megaparsec/4 kiloparsec = 10⁵.

 

[PAllen]

It looks correct to me - the ratio 400 megaparsec/4 kiloparsec = 10⁵.

Oops, didn't notice the mega/kilo ...

 

[Borg]

Hmm, something's up today on APOD.

 

[mfb]

There is a LIGO press conference (https://aas.org/aas-briefing-webcast) later today. 10:15 am PDT, 17:15 UTC, 19:15 in central Europe. Another one is scheduled for 4 hours later.

 

[m4r35n357]

Here is the abstract. Full paper is available too.

 

[mfb]

Short summary: Another clear (>5sigma) signal, apart from that nothing that would be above the background. 14 and 8 solar masses merged to form a black hole of 21 solar masses and 1 solar mass as gravitational waves. Similar distance as the previous event, but in a different direction. The signal was less prominent (you don't see it by eye in the strain curve), but could be tracked over a longer time.

 

[Jonathan Scott]

I was wondering whether a matching event had been detected in any part of the electromagnetic spectrum, but according to the astronomy.com article there was an unfortunate glitch: http://astronomy.com/news/2016/06/ligo-detects-a-second-set-of-gravitational-waves

Hanna and other LIGO scientists received text alerts almost instantaneously on Christmas night and then quickly rallied to analyze the signal. But the next step wasn’t automated.

LIGO is supposed to tip off hundreds of scientists working on more than 60 partner teams so they can try and train their telescopes onto the source, which could have come from anywhere across a vast region of the sky.

The holiday timing proved a perfect storm that stopped the team from notifying the larger astronomy community until more than 36 hours later. Amid the rumors and secrecy surrounding the initial signal, LIGO scientists couldn’t get the proper permissions to approve a community-wide alert.

 

[ProfChuck]

An important prediction of relativity is that G waves and EM waves propagate at the same velocity in the absence of time dispersion. EM propagation can be slowed by refractive index and radiative transfer but there is no clear model for a similar phenomena affecting G waves. Simultaneous detection of G and EM waves from an event will be of significant interest.

 

[Jonathan Scott]

The really interesting point is that according to the usual standard interpretation of General Relativity, no significant electromagnetic radiation is expected from a black hole merger event, but there was an apparent gamma-ray burst detected by the Fermi Gamma-ray Burst Monitor within about half a second of the first gravitational wave event. This means one of three things: the gamma-ray burst detection was spurious (unrelated or background noise), the event was not a simple black hole merger but rather a more complex physical event (for example some people have suggested some sort of merger occurring inside a star) or that General Relativity isn't quite right in that extreme situation. If an apparent gamma-ray burst accompanies another detection that would greatly reduce the probability of it being spurious, which would suggest exciting new physics.

 

[PAllen]

The really interesting point is that according to the usual standard interpretation of General Relativity, no significant electromagnetic radiation is expected from a black hole merger event, but there was an apparent gamma-ray burst detected by the Fermi Gamma-ray Burst Monitor within about half a second of the first gravitational wave event. This means one of three things: the gamma-ray burst detection was spurious (unrelated or background noise), the event was not a simple black hole merger but rather a more complex physical event (for example some people have suggested some sort of merger occurring inside a star) or that General Relativity isn't quite right in that extreme situation. If an apparent gamma-ray burst accompanies another detection that would greatly reduce the probability of it being spurious, which would suggest exciting new physics.

Weakening this finding is failure to detect this signal in other detectors that should have seen it (and that looked carefully for it, e.g. the INTEGRAL detector), and the the random chance probability (given the wide search area) could be as high as 2.8%, depending on assumptions uses (per the paper reporting this find). Using standard priors, the paper quoted .2% chance of coincidence, but noted that other assumptions could lead to the much higher coincidence figure.

To me, this is most likely a non-observation given the whole context. That would obviously change if some future similar detection were made.

 

[mfb]

We'll probably know in a year, with the second LIGO run. and now without necessity to keep the events somewhat secret.

 

[websterling]

there was an apparent gamma-ray burst detected by the Fermi Gamma-ray Burst Monitor

Actually the "burst" was most likely due to improper statistical modeling of a background fluctuation according to this paper on the arXiv and accepted to the Astrophysical Journal Letters- "On the GBM event seen 0.4 sec after GW 150914"

From the abstract- "We find that after proper accounting for low count statistics, the GBM transient event at 0.4 s after GW 150914 is likely not due to an astrophysical source, but consistent with a background fluctuation." The new statistical modeling is said to be a major advancement in detecting low count events with the GBM.

Ethan Siegel (Starts With A Bang) also has an article "NASA's Big Mistake: LIGO's Merging Black Holes Were Invisible After All"