For the first time, gravitational waves and light waves were discovered from the same event - the merger of two neutron stars

In an unprecedented manner, dozens of studies are published today, many of them in the journals Nature and Science, analyzing the astronomical event, some led by scientists from Tel Aviv University. Among them: locating the galaxy where the merger took place, 120 million light-years away from us, understanding the explosion processes, and identifying such events as the source of a variety of heavy metals found on Earth - including gold and uranium.

See another news on the subject: For the first time, a collision and merger of two neutron stars was observed

A discovery from August 17.8.17, 2016 is making waves in the scientific community all over the world: the two detectors of an American project called LIGO and a European detector called Virgo picked up gravitational waves from an event of the merger of two neutron stars somewhere in the universe, and at the same time the massive explosion was observed with the help of a large variety of telescopes on the globe the country and in space. The discovery confirmed a previous sensational discovery, from September XNUMX, in which gravitational waves from the merger of two black holes were recorded for the first time in history, but there was no visible explosion.

"The existence of gravitational waves was predicted by Albert Einstein about a century ago, within the framework of the theory of general relativity," explains Prof. Ehud Naker from the Department of Astrophysics at Tel Aviv University's School of Physics and Astronomy. "These are the waves that are created and spread in the universe following a particularly violent event: the merging of two bodies of enormous mass and density, mainly black holes and neutron stars, which move around each other at a speed approaching the speed of light. Since the 70s, scientists have been working on designing and building detectors that would be sensitive enough to pick up the waves, which are extremely weak. In the last year, this finally came to the hands of a team in the USA, who won the Nobel Prize this year for their discovery."

Prof. Dobi Poznansky, also an astronomer from Tel Aviv University, adds: "It is difficult to exaggerate the importance of simultaneous discoveries of gravitational waves and radiation. This is a discovery that opens a new era in the study of the universe. Until recently, we were able to observe the universe almost exclusively through the light waves that reach us - the sense of sight. The ability to also receive gravitational waves is analogous to the sense of touch. Today we have the ability to explore the universe through the combination of both senses. to see and touch at the same time.'

The astronomical community has been preparing for this day for several years, and as soon as news of the discovery of gravitational waves from a neutron star merger event became known, most telescopes, on Earth and in space, were directed to the general area from which the waves came, with the aim of finding the accompanying explosion by measuring the radiation Electromagnetic - from gamma radiation, through visible light, to radio waves (this is in contrast to the first discovery of gravitational waves, about a year ago, which originated from the merger of two black holes, which apparently do not emit electromagnetic radiation at all). Scientists from Tel Aviv University are leading a significant part of the effort, both observational and theoretical - analyzing the observations and deciphering them.

In the video: the two stars revolve around each other in progressively smaller circles. When the distance between them is already very small, they rotate hundreds of revolutions per second, until finally they collide with a tremendous explosion. The collision releases powerful jets of particles, and creates gravitational waves that spread to the vastness of the universe at the speed of light. Electromagnetic radiation of all wavelengths is also released from the event, which is picked up and studied by astronomers on Earth. 

Dr. Yair Harkabi, who is currently in training at the University of Santa Barbara in California, and will soon join the Department of Astronomy at Tel Aviv University, led one of the groups that located the exact location of the event: a galaxy called NGC4993, which is 'in our neighborhood' in the universe - 'only' approx. -120 million light years from Earth. Prof. Dobi Poznansky, Prof. Dan Maoz from Tel Aviv University and their students are also partners in this research, which is published today in the journal 'Nature'. "When we pointed the telescope at the event area, we discovered an object that faded in brightness 100 times in a few days, and very quickly turned from blue to red," says Dr. Harkabi. "This behavior is unlike anything we know. Thanks to our network of telescopes at Las Cumbres Observatory spread around the world, we could monitor the rapid change of the object every few hours, and witness its rapid decay in real time. The data we collected will teach us about the processes that take place in the fusion of neutron stars and their importance in the creation of the materials that make up our universe.'

What is the origin of gold in the universe?

Prof. Ehud Naker and research student Or Gottlieb, also from Tel Aviv University, lead the theoretical analysis for another group of scientists led by researchers from the California Institute of Technology (Caltech). "For several years now, we have been developing theoretical predictions of what the explosion from the merger of neutron stars will look like at all wavelengths," says Prof. Necker. "As often happens, nature is more creative than us, and besides our predictions that have come true, for example in the field of radio, there are surprising characteristics in the explosion and more work is required to understand them," says Prof. Necker. "One of the interesting results that emerges from the analysis of the observations is the elements that make up the material blown away in the explosion. Until this discovery, we did not know when and where in the universe about half of the elements that are heavier than iron are created, despite their importance in our lives. Today, in light of observations, we can almost certainly say that most of the gold in the universe, including my wedding ring, originated from neutron star mergers. The same goes for uranium, for example, and many other metals.' Prof. Zvi Piren and Dr. Assaf Horesh from the Hebrew University, and Prof. Eran Ofek from the Weizmann Institute are also involved in this research, and it is published today in a series of articles in the journal Science.

"We have no doubt that this is just the beginning," concludes Prof. Dan Maoz. "The ability to detect light and gravitational waves together heralds a new era in astronomy, and we expect many surprising discoveries in the coming years."

See more on the subject on the science website:

• Einstein - the man who started to take us out of the matrix: there are gravitational waves!
• Nobel Prize in Physics for the discovery of gravitational waves
• "The winners of the Nobel Prize in Physics were themselves surprised by the strength of the signal of the first gravitational wave event"
• A collaboration between three observatories resulted in another discovery of gravitational waves
• A new detector will determine the origin of gravitational waves
• A third gravitational wave event has been discovered; Confirms the existence of a new type of black holes
• Proof of Einstein's theory of general relativity: "The discovery of gravitational waves opens a new window to the universe"