The First Discovery of a Binary Neutron Star Merger and an Electromagnetic Counterpart - Dr. Assaf Horesh

New light source at the NGC4993 Galaxy

On August 17 2017 the LIGO detector has made the first discovery of gravitational waves from a Neutron star merger. This type of event was predicted about 30 years ago by several scientists including Prof. Tsvi Piran (Hebrew University). Before this discovery only three gravitational wave events have been detected (since 2015), all of them originating from black hole mergers. This discovery is also unique as this is the first time that electromagnetic emission has been discovered from a gravitational wave source. Two seconds after GW170817 was detected, the space satellite Fermi has detected a short gamma-ray burst in a location consistent with the location of the gravitational wave event. Following this discovery, astronomers around the world have started searching for electromagnetic emission across the spectrum including the ultra-violet, optical, infra-red, X-rays and radio. A team from the U.S. was the first to announce the discovery of an optical counterpart for GW170817. This discovery helped to pinpoint the source to a galaxy at a distance of 130 million light years. Many other groups have detected the counterpart shortly after in optical, infrared and ultraviolet light and have undertaken follow-up campaigns for many days after the event, collecting every bit of information they can. Dr. Assaf Horesh and Prof. Tsvi Piran are members of one of the international teams that performed a detailed analysis of the infrared and optical emission from the source. The team found that as predicted, a large amount of heavy elements have been forged in the merger event, elements such as gold and platinum. Dr. Horesh is also a member of a small team of scientists that has been conducting a search for radio emission from the merger event. Radio emission is expected to arise at late time as the material that is ejected during the merger, interacts with the surrounding material, creating a shockwave. Initially, the radio team did not detect any radio emission. Only 16 days after the initial discovery, radio emission has finally been detected, also for the first time in this type of event. The radio emission is now getting brighter and analysis of this emission can answer many questions such as whether a powerful jet has been formed in the event, and what is the velocity and energy in the ejected material. Overall this discovery symbolizes a new era of gravitational wave astronomy.