### "We are hearing the universe"

When we describe a geometric space, we need to define a metric, or in other words a way to measure distances: in particular in general relativity we use the tensor metric, $g_{\mu \nu}$. Supposing the existence of gravitational waves, it is possible to calculate their effect on the radiation coming from some cosmic objects like a binary or a couple of merging black holes.
On September 14, 2015, within the first two days of Advanced LIGO's operation, the researchers detected a signal so strong that it could be seen by eye. The most intense portion of the signal lasted for about 0.2 s and was observed in both detectors, with a combined signal-to-noise ratio of 24. Fittingly, this first gravitational wave signal, dubbed GW150914, arrived less than two months before the 100-year anniversary of the publication of Einstein's general relativity theory.(1)
The LIGO detectors have observed gravitational waves from the merger of two stellar-mass black holes. The detected waveform matches the predictions of general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. 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.(2)
The story is at the beginning!
We know that the black holes were 29 and 36 solar masses. We are hearing the universe.
Gaby González

(1) Emanuele Berti (2016), The First Sounds of Merging Black Holes, Physics 9, 17