Multi-messenger astrophysics 

Multi-messenger astrophysics uses the information provided by gravitational, weak and strong forces to understand the Universe. These carriers provide information not yet exploited, qualitatively different and complementary to electromagnetic radiation, expanding our view of the astropysical phenomena.

Gravitational Waves

Gravitational waves are ripples in the fabric of spacetime that are generated by accelerated masses. Gravitational waves were predicted by Albert Einstein's theory of general relativity in 1916 as a mathematical consequence of his theory of General Relativity. His initial prediction was that they would travel with speed of light but would not carry energy and would thus not be detectable. In the 1950, new calcuations with the help of the Sticky Bead Argument, lead to the conclusion that Graviational Waves do carry energy. The  first indirect evidence for their existence came in 1974 from the observed orbital decay of the Hulse-Taylor binary pulsar. In 2015 the Laser Interferometer Gravitational-wave Observatory (LIGO) physically sensed the undulations in spacetime caused by gravitational waves generated by two colliding black holes 1.3 billion light-years away, hence providing their first direct evidence.

On October 16, 2017, the LIGO Scientific Collaboration, Virgo Collaboration, and its partners announced the first observation of gravitational-waves from a pair of inspiraling neutron stars, a cosmic event that was observed with both gravitational waves and electromagnetic wavelengths. This occured on August 17, 2017. The gravitational wave signal, designated GW 170817, had a duration of approximately 100 seconds. The analysis of the arrival time of the GW at the three detector locations (two LIGO and one Virgo) yielded an approximate angular direction to the source. A short gamma-ray burst, designated GRB 170817A was detected independently by the Fermi and INTEGRAL spacecrafts, beginning 1.7 seconds after the peak of the GW merger signal, and originating in an area of the sky which overlapped the gravitational wave position, providing further constraints to the localisation of the source. Optical, x-ray, radio, infrared, and gamma ray telescopes, as well as neutrino detectors all participated in the post-GW170817 observations, believed to be the most widely studied single astronomical event in human history.

Sky localization of the gravitational, gamma-ray and optical signals off GW170817. Left: LIGO (light green), LIGO-Virgo (dark green), Fermi and INTEGRAL triangulation (light blue) and Fermi GBM (dark blue) localization; Right: localization of the host galaxy NGC 4993 by 1M2H Collaboration at 10.9 hours after the merger and the DLT40 pre-discovery image; adapted from P. Abbott et al., ApJL 848 (2017) L12.