On February 11, 2016, the National Science Foundation and the leaders of the LIGO collaboration (Laser Interferometer Gravitational-Wave Observatory) announced the first direct detection of a gravitational signal. The signal that was discovered baptized as GW150914 by the date of September 14, 2015, fits very well with the waveform predicted by general relativity for the fusion of two black holes. Although this discovery must still be confirmed through independent experiments (VIRGO or KAGRA), the fact that the same signal has been discovered in the two LIGO detectors (which are 3,002 km apart) almost simultaneously leaves very little doubt about the astrophysical origin of the signal detected. The detection of GW150914 is extremely important not only to provide a direct verification of the existence of gravitational waves, but also because it opens a new window in astronomy and offers the possibility of exploring (or "listening") the universe by completely new methods. . The fact that the GW150914 signal will fit with the waveform calculated for the fusion of two black holes, provides the first observation of a binary black hole system, where the two black holes, after rotating around each other, merge and they form a single black hole. The fact that the signal coincides with the predictions of general relativity, implies strong proofs for its validity in the regime where the gravitational interactions are strong and dynamic. Future observations with LIGO, VIRGO and KAGRA should lead to even stronger evidence of general relativity and the structure of black holes and binary systems of black holes or neutron stars.