MG15 - Talk detail

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The discovery of the gravitational-wave pulse GW170817 by the LIGO/Virgo collaboration (Abbott et al. 2017) followed by the discovery of short gamma-ray pulse GRB170817A that was detected 2 seconds later by the Fermi space observatory (Goldstein et al. 2017) provided direct proof for the hypothesis of collisions of neutron stars for observed short gamma-ray bursts. Moreover, the discovery of optical emission in the bright nearby galaxy NGC4993 provides the insight into the evolutionary status of the binary star system that generated the double neutron star, which on August 17 of 2017 gave birth to a gravitational wave phenomenon accompanied by an electromagnetic flare. NGC 4993 is an early-type galaxy (Sadler at al. 2017). Such galaxies are characterized by suppressed star formation (Karachentsev et al., 2013), which is confirmed in the case of NGC 4993 by direct spectroscopic data in the ultraviolet and infrared. Thus, ultraviolet observations suggest a star formation rate of SFR (NUV) ~ 0.003 Mʘ/yr for stars with masses greater than 5 Mʘ. This is consistent with the upper limit obtained from infrared observations. It is evident that this galaxy contained no massive stars capable of generating neutron stars for several billion years. This means that the recorded gravitational-wave event cannot be associated with the collapse of the fast-rotating core of a massive star. In other words, we are dealing with a merger in an old system of two neutron stars several billion years old (Lipunov, 2017b). We proved this statement by applying the method of population synthesis of binary systems to the NGC 4993 galaxy. We present one of the possible scenarios for the evolution of a system of two massive stars leading to the neutron-star merger recorded on August 17, 2017 by the gravitational-wave detectors of the LIGO/Virgo collaboration. This evolutionary track is one of the many millions of those used in the population synthesis (Lipunov et al. 1996). The track is reproduced using the open online version of the Scenario Machine (Nazin et al. 1998).

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