AUTHOR=Pian Elena 

TITLE=Mergers of Binary Neutron Star Systems: A Multimessenger Revolution

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=7

YEAR=2021

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2020.609460

DOI=10.3389/fspas.2020.609460

ISSN=2296-987X

ABSTRACT=<p>On August 17, 2017, less than two years after the direct detection of gravitational radiation from the merger of two<inline-formula id="inf1"><mml:math id="mml-math1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo></mml:math></inline-formula>30 <inline-formula id="inf2"><mml:math id="mml-math2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>M</mml:mtext><mml:mo>⊙</mml:mo></mml:msub></mml:mrow></mml:math></inline-formula> black holes, a binary neutron star merger was identified as the source of a gravitational wave signal of <inline-formula id="inf3"><mml:math id="mml-math3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo></mml:math></inline-formula>100 s duration that occurred at less than 50 Mpc from Earth. A short gamma-ray burst was independently identified in the same sky area by the <italic>Fermi</italic> and <italic>INTEGRAL</italic> satellites for high energy astrophysics, which turned out to be associated with the gravitational event. Prompt follow-up observations at all wavelengths led first to the detection of an optical and infrared source located in the spheroidal Galaxy NGC4993 and, with a delay of <inline-formula id="inf4"><mml:math id="mml-math4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo></mml:math></inline-formula>10 days, to the detection of radio and X-ray signals. This article revisits these observations and focusses on the early optical/infrared source, which was thermal in nature and powered by the radioactive decay of the unstable isotopes of elements synthesized via rapid neutron capture during the merger and in the phases immediately following it. The far-reaching consequences of this event for cosmic nucleosynthesis and for the history of heavy elements formation in the Universe are also illustrated.</p>