Just after the Nobel Prize was awarded for the discovery of gravitational waves from the merger of two black holes, a registration of the gravitational signal from neutron stars merger was announced. By definition, black holes are “black”, i.e. they do not emit any electromagnetic radiation, and so all gravitational waves from from black hole mergers were observed in total “silence” (thus far, four such events were recorded). This makes it practically impossible to precisely localize the signal source. The uniqueness of the new event is that it represents a merger of two neutron stars, and in this case a “flash” can occur in the entire range of electromagnetic waves – in visible light, radio waves, X-ray and ultraviolet ranges, gamma rays.
The gravitational signal was registered on August 17, 2017 by LIGO and Virgo detectors. Two seconds after the gravitational signal, the Fermi space telescope detected a gamma-ray flash. Based on these data, it was possible to significantly narrow down the search zone in the sky. Within 10 hours, a telescope in Chile found the source galaxy, after which urgent messages were sent out to observatories over the world. Over the next few days, more than 70 telescopes (including space telescopes) were observing this galaxy. For the first time in the history of astronomy, one cosmic object was simultaneously observed by such a large number of instruments. The results of the study were published on Monday, October 16, in 40 articles in leading scientific journals.
Thus, the source of gravitational waves was localized in the sky for the first time. The galaxy NGC 4993, in which the neutron stars merged, is about 130 million light-years away from us. This means that the merger itself happened in this galaxy 130 million years ago, and only now the signals have reached us. Although these are very large numbers, by cosmological standards this is not far away.
The importance of the discovery is that it confirms the correctness of the theory of gravitation in strong regime. This gives us confidence that we are on the right track in understanding the structure of our world at the most fundamental level. But even more important is that this is not just a scientific discovery. In fact, we are witnessing the birth of a new era in astronomy, when not only we will “see” events in space not only with the help of electromagnetic radiation, but also we will be able to “probe” the most remote corners of the universe with gravitational waves.
It is remarkable that Kazakh astronomers are also related to this historical moment in science. The authors of the main paper about the discovery include several researchers from Fesenkov Astrophysical Institute (Krugov M.A., Kusakin A.V., Reva I.V.), who observed the optical afterglow associated with the received gravitational signal in the Tien-Shan high-altitude Observatory on a 1-meter Zeiss-1000 telescope. These observations have become a part of this grandiose discovery. Regular observations of the afterglows of gamma-ray bursts at the observatories of Fesenkov Astrophysical Institute are funded by the Government of the Republic of Kazakhstan within the grant No. 0075/GF4.