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Space: gravitational wave captured from neutron stars fusion

Space: gravitational wave captured from neutron stars fusion
Foto: skeeze / 

Rome - For the first time ever in the history of star gazing, a gravitational wave produced by the fusion of two neutron stars was detected, with its associated explosion and electromagnetic radiation, from radio waves to gamma rays. It is the first time that a cosmic event is observed through both gravitational and electromagnetic waves, thus launching the era of multi-message astronomy, which extends our ability to "see" and "listen" to the universe. The discovery was made possible by the synergy between the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and the VIRGO observatory in Europe, combined with the observations and surveys of the electromagnetic bands from 70 earth based telescopes, including REM, VST, VLT, and space observatories like Fermi and Integral, Swift, Chandra, Hubble, which allowed to clearly characterize the origin of the wave. Italy is one of the leading world players in this extraordinary event: the Istituto nazionale di fisica nucleare (National Institute of Nuclear Physics - Infn) founded the gravitational wave detector VIRGO, the Istituto nazionale di astrofisica (National Institute of Astrophysics - Inaf) was one of the first in the world to 'photograph', and hence recognize and characterize, the source known as AT2017gfo using land and space based instruments, and the Agenzia spaziale italiana (Italian Space Agency - Asi) is involved in missions dedicated to high energy astrophysics. The event took place 130 million light years from us, at the edges of galaxy NGC4993, in the direction of the Hydra constellation. The two neutron stars, at the end of their inexorable and increasingly frenetic approach, spiraled around each other emitting gravitational waves that were observed for nearly 100 seconds. When the stars collided, they emitted a flash of light in the form of gamma rays, which was observed in space by Nasa's Fermi satellite, and then confirmed by Esa's Integral satellite, around two seconds after the gravitational waves. In the days and weeks following the cosmic crash, electromagnetic waves were identified on other wavelengths, including x-rays, ultraviolet rays, visible light, infra-red rays and radio waves. The Italian researchers at Inaf were able to collect and analyze an invaluable amount of information on this event, thanks to the REM (Rapid Eye Mount), ESO VST (VLT Survey Telescope) and VLT telescopes. The data collected from space by the Integral and Swift missions, with the participation of Asi, CHANDRA (Nasa) and Hubble (NASA-ESA), were also a decisive contributing factor. Astronomers had an unprecedented opportunity to survey the collision of two neutron stars with all the best instruments at our disposal. Observations made through the Very Large Telescope (VLT) led by Italian researchers reveal evidence of the synthesis of heavy elements, like gold and platinum, after the explosion. This resolved the enduring mystery regarding the origin of nearly half of the elements that are heavier than iron. The data collected by Nasa's space telescope Hubble point to the same conclusions. Furthermore, scientists had the first direct confirmation that neutron star collisions give rise to the short-lived Gamma-Ray Bursts (GRBs). The LIGO-VIRGO results were published on 16 October in the Physical Review Letters, while many other articles of the LIGO and VIRGO collaborations, and the astronomer community associated with space telescopes like Integral, Fermi, Swift and Agile were presented to or accepted by several reviews, many of which were co-written or authored by Italian researchers. Two articles published by Nature had Inaf scientists as main authors. The gravitational signal, known as GW170817, was recorded on 17 August at 2:41 p.m. Italian time. The two LIGO twin detectors located in Hanford, Washington, and Livingston, Louisiana, detected the event, while the information collected by the third detector, VIRGO, near Pisa in Italy, enabled the precise location the cosmic event. Almost at the same time, on 17 August, the Gamma-ray Burst Monitor of NASA's Fermi space telescope detected a Gamma Ray Burst, which was later confirmed by the Integral satellite. The LIGO-VIRGO analysis software put the two signals together, deducing that it was highly improbable that they were caused by a random coincidence. Further automatic analysis highlighted the presence of a coinciding gravitational signal in the second LIGO detector.