Second detection of gravitational waves by LIGO

[torsion]

LIGO scientist did it again! The signal was about 1 second long and they could see about 27 orbits of the two black holes before they merged. This was about 0.25s compared to the first detection.

Due to the many cycles, they could put a better measure of the spin of the black holes. Unfortunately from only one and measured a spin of '0.2'.

With this second detection LIGO is now 'observing' gravitational waves. Currently the machines are undergoing maintenance to improve the sensitivity by about two.

More details:

https://www.ligo.caltech.edu/news/ligo20160615

http://www.aciga.org.au/news/gw151226

PRL publication: http://link.aps.org/doi/10.1103/PhysRevLett.116.241103

[rustigsmed]

massive news!

[janoskiss]

Very cool. These will become very common events within a few years. It's like when the first planets were detected: was a big deal then, now routine.

Next big challenge will be to see something other than colliding black holes. Maybe neutron stars... Like we went from Jupiter sized planets to Earth sized ones.

It's all very exciting stuff.

[DavidU]

Thats big news ! Never thought it would happen so soon.

[RobF]

Yes, exciting times to get a 2nd signal so quickly!

[janoskiss]

They detect one of these every couple of weeks or so. The reason we don't hear about them is that the analysis takes so long and the scientists won't reveal anything until they are absolutely sure that it's the real deal and not noise or (pardon the pun) interference from other sources.

In these early stages of new discovery experimental physicists are very stringent. They want to be very certain that what they're seeing is real before publishing it. To do things properly they have the Five Sigma rule, which means they are better than 99.9999% sure, or there is less than one in a million chance they're wrong (winning Tattslotto kind of odds). Sixty Symbols explains:
https://youtu.be/ThP51oPttS0

[torsion]

Not quite, but hopefully in the future it will indeed be more regular, only time will tell. The second event was observed in the same 4 month observation run as the first event. And even a possible third event has been observed, but the signal to noise ration deemed to be to low.

The data coming out if the LIGO detectors are analysed for triggers almost in real-time. When a 'waveform', which represents a gravitational wave event, matches the time series, alarm bells will go off. Then human checks are performed to see if it is not an false alarm (slamming doors, wind, earth quakes etc). If all is good, then the time series on which the waveform had a nice fit will be further analysed (although the whole data set will be used for background noise characterisations).


That is correct, there is a rigorous procedure in place to make sure the event is real and not an artefact from the machine, anthropogenic or other terrestrial noise.

Then the analyses (e.g. Einsteins general relativity) will tell what the source of the event is all about (e.g. primary and secondary mass, their spin, final mass etc). This will take time as well.

Once all is satisfied the event will be reported to the scientific and general community.

Hopefully in the not to distant future some other than a black hole mergers will be observed:) Especially something with a possible EM counter part such a neutron star - black hole merger.