Collision of Two Neutron Stars Sends Ripples Through Space-time – and Scientific Community

Israeli astronomers and astrophysicists collaborated with scientists from all over the world in uncovering this precedent-setting discovery

An artist's rendering, obtained from the European Southern Observatory, shows two tiny but very dense neutron stars merging and exploding as a kilonova, October 16, 2017.
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Two months ago, an event that took only a fraction of a second sent shock waves through the international scientific community. A collision between two neutron stars and their subsequent merger into a black hole – only 130 million years ago, in a galaxy about 100 million light-years from here – was captured in August by a number of telescopes and other scientific instruments for detecting gravitational waves. The collision, known as a kilonova, has become one of the most important scientific events in cosmology.

The data recorded from the event provides the first visual evidence for the formation of gravitational waves, which were predicted by Albert Einstein about 100 years ago. The official announcement was made on Monday at simultaneous press conferences by the Laser Interferometer Gravitational-Wave Observatory and Virgo, the scientific umbrella organizations overseeing the worldwide search for gravitational waves, but rumors of the discovery have been floating around scientific circles for months.

On August 17, a number of scientific groups picked up on a collision that happened in the nearby galaxy NGC 4993. The merging of the two neutron stars, the explosion and the formation of the black hole took less than a thousandth of a second.

Neutron stars are the smallest and densest stars and result from a large star collapsing into itself so that the remaining matter is only neutrons.

An image obtained from the European Southern Observatory shows the galaxy NGC 4993, about 130 million light-years from Earth, October 16, 2017.
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Among the scientists from all over the world who are participating in the various projects surrounding the event are astronomers and astrophysicists from Tel Aviv University, the Hebrew University of Jerusalem and the Weizmann Institute of Science in Rehovot.

The discoveries have led to a number of papers in the most prestigious scientific journals, which are being published now. While the different papers concern a number of scientific disciplines, in general they all revolve around the fundamental questions of how the universe and galaxies were formed, what physical forces and processes were involved and how elements were created, as well as the explanation of various phenomena such as gamma ray radiation.

The Tel Aviv University telescope located in Mitzpeh Ramon, part of the Las Cumbres Observatory telescope array, measured the radiation emitted from the event. Prof. Dov Poznanski of Tel Aviv University, who took part in the research along with Prof. Dan Maoz and their students, published an article on the topic that is being released in the scientific journal Nature on Monday. It is difficult to overstate the importance of the discovery of both the gravitational waves and the radiation, says Poznanski. “It opens a new era in cosmology.”

Until recently it was possible to study the universe almost exclusively through light that reaches us. "The ability to detect gravitational waves is like gaining an extra sense, comparable to the sense of touch," he says. After the discovery of the gravitational waves was revealed, most telescopes on Earth and in space were turned to the region of the neutron star collision in an attempt to find the accompanying explosion by measuring the electromagnetic radiation coming from it, from gamma radiation through the visual spectrum and all the way to radio waves.

The discovery was especially poignant this year because three U.S. scientists behind the LIGO project, Rainer Weiss, Barry Barish and Kip Thorne, won the 2017 Nobel Prize in physics two weeks ago for developing the ability for detecting gravitational waves.

Prof. Eran Ofek of the Weizmann Institute said that while the gravitational waves are only detected for a fraction of a second, other electromagnetic radiation from the merger of the stars can arrive over a period of days, and in more common forms, such as X-rays, gamma rays and radio waves. “Many telescopes noticed this radiation, which appeared as a new point in the sky, but at first we were not sure that this point was really the merger of the stars that the detectors discovered,” said Ofek.