[LINK] Three links on the detection of gravitational waves by LIGO

[rfmcdonald]

First, from Bad Astronomy's Phil Plait, "LIGO Sees First Ever Gravitational Waves as Two Black Holes Eat Each Other".

Gravitational waves (not to be confused with gravity waves, which are a totally different thing) are ripples in the fabric of spacetime, caused when a massive object is accelerated. By the time they get here from distant astronomical objects, the waves have incredibly low energy and are phenomenally difficult to detect, which is why it’s taken a century to discover them since they were first predicted by Einstein’s Theory of General Relativity. Essentially every other prediction of GR has been found to be correct, but the existence of gravitational waves has been maddeningly difficult to prove directly.

Until now. And what caused the gravitational waves they detected at the Laser Interferometer Gravitational-Wave Observatory is as amazing and mind-blowing as the waves themselves: They caught the death spiral and aftermath of two huge black holes 1.3 billion light-years from Earth, merging together in a titanic and catastrophically violent event.

Mind you, we’ve had some good evidence such binary black holes existed before this, but this new result pretty much proves they exist and that, over time, they eventually collide and merge. That’s huge.

The black holes had masses of 36 and 29 times the mass of the Sun before they merged. After they merged they created a single black hole with a mass of 62 times that of the Sun. You may notice those masses don’t add up right; there’s 3 solar masses missing. That mass didn’t just disappear! It was converted into energy: the energy of the gravitational waves themselves. And the amount of energy is staggering: This single event released as much energy as the Sun does in 15 trillion years.

I know. There is nothing about this story that isn’t incredibly cool.

Second, Gizmodo's Maddie Stone and her "Holy Shit! Scientists Have Confirmed the Existence of Gravitational Waves".

That announcement has just come. Gravitational waves were observed on September 14th, 2015, at 5:51 am ET by both of the LIGO detectors, located in Livingston, Louisiana, and Hanford, Washington. The source? A supermassive black hole collision that took place 1.3 billion years ago. When it occurred, about three times the mass of the sun was converted to energy in a fraction of a second.

[. . .]

After a series of upgrades that lasted from 2010 to 2015, LIGO was back online this past fall. With more powerful lasers and improved system for isolating the experiment from vibrations in the ground, the prospects of detecting the first gravitational waves have never looked better. Some scientists even predicted that we’d have our first positive detection in 2016—but few could have known how quickly it would come.

In fact, LIGO saw gravitational waves almost immediately. The team then spent the entire fall exhaustively investigating potential instrumental and environmental disturbances to confirm that the signal was real.

According to Einstein’s theory of relativity, when a pair of black holes orbit on another, they lose energy slowly, causing them to creep gradually closer. In the final minutes of their merger, they speed up considerably, until finally, moving at about half the speed of light, they bash together, forming a larger black hole. A tremendous burst of energy is released, propagating through space as gravitational waves.

The two black holes behind the all the hubbub are 29 and 36 times the mass of the Sun, respectively. During the peak of their cosmic collision, LIGO researchers estimate that their power output was 50 times that of the entire visible universe.

Third, here is the paper in Physical Review Letters, "Observation of Gravitational Waves from a Binary Black Hole Merger".

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 −180   Mpc corresponding to a redshift z=0.09 +0.03 −0.04 . In the source frame, the initial black hole masses are 36 +5 −4 M ⊙ and 29 +4 −4 M ⊙ , and the final black hole mass is 62 +4 −4 M ⊙ , with 3.0 +0.5 −0.5 M ⊙ c 2 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.