A tool has been developed that will make it possible to discover neutron star mergers that are good candidates for studying gravitational waves

In an article recently published in the prestigious journal Nature, Dr. Ehud Naker from Tel Aviv University and Prof. Zvi Piren from the Hebrew University of Jerusalem discovered a radio signal that will help find mergers of neutron stars, which are currently being sought around the world in order to find gravitational waves.

Many scientists see gravitational waves, small fluctuations in the fabric of space-time, as the sounds of the universe. Just as the sound waves complete the visible image in our daily life, so the gravitational waves will in the future complete the image of the universe obtained by telescopes. Although Einstein predicted the existence of gravitational waves as early as 1918, today, almost a hundred years later, the search for them is still underway.

In an article recently published in the prestigious journal Nature, Dr. Ehud Naker from Tel Aviv University and Prof. Zvi Piren from the Hebrew University of Jerusalem discovered a radio signal that will help find mergers of neutron stars, which are currently being sought around the world in order to find gravitational waves.

These days, a number of huge detectors are placed in Europe, the USA, Japan and Australia, all of which have the purpose of detecting gravitational waves that reach the Earth from the universe. Although all motion causes gravitational waves, to create gravitational waves strong enough to detect requires a huge mass moving at a speed close to the speed of light. The strongest source from which scientists expect gravitational waves is the process of merging two neutron stars (very compressed stars whose mass is the same as the Sun's and only a few kilometers in size). But such mergers are extremely rare and occur once every hundred thousand years in the entire galaxy. The detectors looking for these signals are required to discover them from vast distances of billions of light years from us (far outside the Milky Way). At such distances the gravitational waves sound like a soft knock on the door.

The problem the researchers face is that many noise sources, from seismic fluctuations to trucks passing near the detector and even distant sea waves, compete with this soft click. How will we know, then, if the detector really picked up a gravitational wave or if it is the sound of a tree falling in a nearby forest? For this, an additional signal is needed that will arrive together with or even after the gravitational wave and confirm the discovery. Astronomers have long asked whether there is a flash of light or other radiation (eg radio) that comes from merging neutron stars. Detecting such a flash near the possible detection of a gravitational wave will allow scientists to peek through the peephole in the door and verify that someone has indeed knocked on the door.

Dr. Necker and Prof. Piren discovered just such a signal. They calculated the interaction between matter thrown in the merger process and the interstellar matter. They showed that the great heat generated in this process emits radio radiation for months and even years after the merger. These radio signals are strong enough to be detected and measured on Earth even from billions of light years away. The world's largest radio telescopes are starting to look for them now, even before the gravitational wave detectors start operating in 2015. Detecting such signals will teach a lot about the rate of neutron star mergers and allow better planning and execution of the search for gravitational waves. Dr. Necker and Prof. Piren claim that the discovery of an unidentified radio flash by Dr. Jeffrey Bauer from the University of California several years ago was the first direct detection of a neutron star merger.