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Chronicle of a global collaboration: the fusion of two neutron stars, a hug of 130 million years

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TololoAugust 17, 2017: Scientists from all over the world who study the Universe witness and analyze online and live a historical event that will mark a before and after in the way we understand the study and the development of Astronomy. The news is spread all over the globe on October 17. In our homes and offices, going on the public transport or walking around, we watch on TV, mobile devices and computers the re-creation of a two neutron stars fusion that occurred 130 million years ago in NGC4993, the largest galaxy in the constellation of Hydra. The event was categorized as 'cataclysmic'. The reason for the media and scientific revolution caused by the phenomenon lies in the fact that it was the first of its kind in history to be recorded, seen and listened simultaneously, thanks to telescopes, radio telescopes, gravitational wave detectors and advanced Internet networks - such as RedCLARA and GÉANT, at regional level - that allowed the collaborative work of almost a hundred researchers from all over the world who contributed to the study.

But, what really happened on that August 17? At 8:35 a.m., NASA's FERMI space telescope detected a gamma-ray eruption from the elliptical galaxy NG4993 in the constellation of Hydra. The eruption is confirmed by INTEGRAL (International Gamma-Ray Astrophysics Laboratory), from the European Space Agency. Fermi and INTEGRAL are the main operating range observatories to date. The first alert was launched into the scientific world; astronomers, radio astronomers, physicists, and astrophysicists, among others, intensified their work of observation and measurement. "These two measurements gave more precision to the origin of the strong gamma emission and since that moment NGC4993 became the center of attention of all the telescopes in the world, especially those that analyze the sky from the southern hemisphere", wrote in his blog the physicist and Doctor in Science, Luis Nuñez.

360 seconds later, the LIGO Hanford gravitational wave observatory (located in the Columbia River drainage basin in Central Washington, near Tri-Cities, United States) triggered its alarm because of the detection of a new vibration by the laser interferometers; 3,002 kilometers far from there, the same waves were picked up by LIGO's "twin" in Louisiana (LIGO Livingston), and in Pisa, Italy, by the Virgo interferometer. This is the event that will soon be associated with the emission of a gravitational wave produced by the fusion of two neutron stars: a kilonova.

"Is the first time we have recorded this kind of fusion of the denser stellar objects of the Universe. The density of neutron stars is equivalent to concentrating the entire mass of the Earth on a sphere of 2km diameter, not 12,000 miles, as our planet has. Neutron stars concentrate the entire mass of the sun in a sphere of 12 km; are smaller than the extent of many cities on the continent. A 'spoonful' of this material would concentrate the entire mass of Mount Everest", points out Nuñez in his blog.

What happened after these six minutes and the mentioned warnings is narrated by Núñez: "Ten hours after the merge detected by LIGO, the Observatory of Las Campanas, located in the Atacama Desert, in northern Chile, detects a visible light at the indicated location. Then, the Las Cumbres Observatory's global network of telescopes confirms that there is a signal close to NGC4993, and in the Space, the SWIFT and Hubble satellites detect an ultraviolet emission. At sunset on August 18, a new search in the southern sky begins, and VISTA (Visible and Infrared Telescope for Astronomy), an impressive 4.1m-diameter reflector telescope at the Paranal Observatory in Chile, also records an event located in the same region, close to NGC4993 and that remains in the sky that night. Dozens of telescopes in Chile competed to record the phenomenon in a scant hour before it was hidden on the horizon.”

The experience at the Cerro Tololo Inter American Observatory, in La Serena, Chile, is counted as follows by the supporting astronomer Kathy Vivas: "Coordinated work was vital not to waste resources and to get the most out of the event. Advanced Internet networks played a key role in this context: the images obtained in Chile were being analyzed in real-time by different groups around the world."

4500 researchers, 70 observatories, 40 countries, all united through advanced Internet networks - Chile observatories are connected by REUNA and RedCLARA, as in all Latin America; LIGO is connected by Internet2, Virgo by GÉANT, among other participating networks around the world - in the analysis of a phenomenon not only attended, registered and measured for the first time in history but also heard (https://halley.uis. A phenomenon that, as explained by the physicist Enrique Zas, Pierre Auger Observatory's representative in Spain, changed the astronomical observation in a definitive way. "All of these combined observations are a unique and unprecedented source of information that allows us to delve deeper into our studies of these cataclysmic phenomena in an exceptional way, and thus entail enormous strides in science. For now, we have confirmed that the origin of at least part of the short bursts of gamma rays is due to the collision of neutron stars, something that until now was only a hypothesis. This data is collected in an article published on October 16 in the Astrophysical Journal Letters, by the collaboration of all these observatories including the Pierre Auger Observatory. It is a gigantic joint effort of many experiments, involving astronomy, astrophysics, particle physics, and the new field of gravitational waves giving rise to an exceptional discovery. Undoubtedly, it marks the beginning of a new form of observation that some have already begun to call "multimessenger astronomy."

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