Multi-messenger astronomy

On 17 August 2017, a coalescence of neutron stars that occurred in the NGC 4993 galaxy (at approximately 130 million light years from us) was observed at the same time by LIGO and Virgo gravitational wave observers and by numerous electromagnetic telescopes (from radio waves to energetic gamma rays) throughout the world. This event, which is still the only one observed of this type, is considered to symbolise the birth of so-called “multi-messenger astronomy”. This new approach to exploring the universe enables the investigation of the same astrophysical event through various cosmic messengers, carriers of different and, in many cases, complementary information.

Artist’s illustration of two merging neutron stars. (© NSF/LIGO/Sonoma State University/A. Simonnet)

Illustration of NASA’s Fermi Gamma-ray Space Telescope (© NASA's Goddard Space Flight Center/Chris Smith (USRA/GESTAR))

Another example of multi-messenger observation arrived in September 2017, when the IceCube experiment in the South Pole detected a cosmic neutrino in combination with very high-energy gamma photons. These were observed by several gamma-ray space telescopes, including the Large Area Telescope of the Fermi satellite, built by NASA and managed with an important contribution from INFN.
Multi-messenger observation made it possible to go back to the source: a “blazar”, i.e. an active galaxy with a supermassive black hole at the centre. It is 4.5 billion light years away from us, in the direction of the Orion constellation.

In futuro, si prevede che osservazioni multimessaggere diventeranno quasi di routine, grazie al potenziamento degli attuali esperimenti e all’arrivo di quelli di nuova generazione. Il futuro osservatorio sotterraneo di onde gravitazionali Einstein Telescope, per esempio, promette di rivelare ogni anno decine o centinaia di eventi di fusione tra stelle di neutroni con controparte elettromagnetica, aprendo la strada a prospettive di ricerca del tutto inedite per la comprensione di numerosi fenomeni cosmici: dalla nucleosintesi degli elementi pesanti fino alla comportamento della materia in condizioni estreme nelle stelle di neutroni, passando per i getti relativistici associati ai lampi di raggi gamma, fino a eventi cosmologici rilevanti.

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