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June 16, 2016
gravitational waves have been until now the only physical phenomenon predicted by Einstein’s General Relativity, which had not been directly observed. Einstein predicted that the masses accelerated emit gravitational radiation, ie waves which pass through spacetime it contracts and expands rhythmically. We can imagine them like ripples on the surface of a pond, which propagate in the cosmos at the speed of light. DEPTH
Gravitational Waves – HISTORY (by the National Institute of Nuclear Physics – INFN)
England, 1685: Isaac Newton suggested that a single universal force is responsible for falling objects and the motion of the planets. It calls gravity. To escape the of the Earth’s gravitational escape velocity of 40,000 km / h is required.
England, 1783: Reverend John Michell speculates, based on the laws of Newton, that the the escape velocity of a star much more massive and compressed the Sun can exceed the speed light. Not even light, therefore, can escape the gravitational field of these objects Michell calls “.
France 1797: the scientist and mathematician Pierre Simon de Laplace offers demonstration mathematical existence of black stars Michell, that Laplace called invisible objects.
Switzerland, 1915: Albert Einstein formulated the theory of general relativity, which describes the space and the time as a single object dimensional curved. Gravity is not a force at a distance but a spacetime deformation created by a massive object.
Germany, 1916: physicist Karl Schwarzschild determines a particular solution of the equations Einstein’s General Relativity, able to describe the gravitational field of the objects now call blacks holes.
Brazil, 1919 the English astrophysicist Arthur Eddington confirmed the predictions of General Relativity occurring during a total eclipse of the Sun that the path of the stars’ light beams is deflected the severity of the sun.
Germany, 1958 based on the Schwarzschild solution, the physicist David Finkelstein provides that a portion of spacetime can be deformed to the point to create a gravity well to which no object can escape.
USA 1963: New Zealand mathematician Roy Kerr extends the Schwarzschild solution to the case of a massive rotating object
USA, 1967, referring to the Finkelstein well and the Schwarzschild solution, the physicist John Wheeler coined at a conference in New York, the term black hole.
England, 1975: applying quantum mechanics and thermodynamics, Stephen Hawking and Jacob Bekenstein show that, by irradiating energy slowly, blacks holes are not entirely “blacks”. It is the birth of the debated Hawking radiation.
US-Europe 2016: scientists of the LIGO-VIRGO collaboration reveal for the first time gravitational waves , providing the first direct evidence of the existence of blacks holes, and thus opening the way to their detailed study
“ I was beside myself with joy and excitement “. With these words, addressed friend physicist Paul Ehrenfest, Albert Einstein describes the excitement, with a lot of heart palpitations, proven exactly a century ago after finding the experimental confirmation, the first of many series, to his theory of the General Relativity .
“ We detected for the first time gravitational waves . ” The historic announcement comes around the world at 16:30, Italian time, on 11 February 2016. “ We saw the waves 
gravity “. Live from ‘ European Gravitational Observatory (Ego) Cascina , in the province of Pisa, to break the news that will revolutionize the approach to the study of the Universe is Fulvio Ricci , spokesman for the international project Virgo, to which Italy participates with the national Institute of Nuclear Physics (INFN).
The first signal of gravitational waves to be picked up was generated by the collision of two blacks holes, collision occurred a billion years ago. The Laser Interferometer Gravitational Ligo- tool-wave Observatory – has pricked the antennae and captured by the United States September 14, 2015, and then be able to interpret it by collaborating with Virgo interferometric gravitational wave detector, which is right in Cascina .
on December 26, 2015, at 4:38 am Italian time, even for the wave detectors gravitational came Santa Claus. Bringing the gift of the second clear signal produced by the ripples of the space-time fabric. Both detectors that make up the Laser Interferometer Gravitational-Wave Observatory (LIGO) have recorded the event, called GW151226.
The observation of a second event of gravitational waves was announced yesterday, during a joint press conference by the scientists of scientific collaborations LIGO and VIRGO, which Italy participates with the National Institute of Nuclear Physics INFN. The tiny ripples in the fabric of spacetime, provided by General Relativity by Albert Einstein a century ago, have been recorded for the second time, again during the first period of data taking ended January 12, 2016, the twins Advanced LIGO interferometers, in the United United (in Livingston in Louisiana, and Hanford in Washington State), at 3:38:53 UTC on 26 December 2015. As with the first revelation, these gravitational waves were produced by the fusion of two blacks holes, process dating back to 1.4 billion years ago.
The study was accepted for publication by the international scientific journal Physical Review Letters that the ’11 last February, had published the article of the discovery of gravitational waves.
After opening new scientific horizons with the first historical observation of gravitational waves, this new measurement confirms that we really got to the heart gravitational astronomy era: that is, we are studying our universe in a completely new way.
observation
the measured waves in this second observation refer to last 27 orbits that blacks holes, mass equal to 14 and 8 solar masses, have come in “spirals down” whirling around each other before they merge and form a single black hole more massive, with a mass equivalent to 21 solar masses. The energy released in the form of gravitational waves is therefore equivalent to about one solar mass.
” This second event – says Fulvio Ricci , INFN researcher and professor at the University of Rome Sapienza, head of the international scientific collaboration VIRGO – has characteristics significantly different from the first . ” “ It is, in fact, generated by lighter blacks holes than the previous signal – continues Ricci – and we have been able to follow its evolution for more time: this allowed us to characterize the system well, despite the relationship between the signal and the background noise was of lesser intensity. The hunt for signals generated from binary systems of blacks holes is also enriched with a third event, weaker than the other two and therefore with a higher probability that it may be a false detection. However, even in this case, attributing to this third event a meaning astrophysical, we would face a third system of blacks holes, which is collapsed to form a final black hole. In essence we are glimpsing the existence of an entire population of blacks holes, the features of which will soon be unveiled in the coming phases of the data taking advanced interferometers , “says Ricci.
A network of interferometers for gravitational astronomy
“ Observers for gravitational waves represent a unique tool to investigate the cosmos , – says Federico Ferrini , director of the European Gravitational Observatory EGO, which houses and manages the interferometer VIRGO – very special because these cosmic messengers lead with it information that would not be able to obtain in any other way “. The gravitational wave signal was recorded by the interferometer in Louisiana with 1.1 milliseconds ahead of the interferometer in Washington state. This measurement, however of great precision, does not allow, however, to pinpoint the source: to do so it is necessary to at least a third interferometer which allows the triangulation. “ When in the autumn of this year the European Virgo interferometer will start operating at the end of the work that will lead, as the two LIGO interferometers, Advanced Configuration (advanced) , – says Gianluca Gems , VIRGO – then it will be possible to restrict the portion of the sky in which took place the merger process of the two blacks holes “. “ This will make a substantial contribution to the new gravitational astronomy and astronomy multi-messenger: we can give the alert to other experiments, both terrestrial and space telescopes to detect gamma photons, cosmic rays and neutrinos, for example, so it is oriented, practically in real time, in the direction of the source to identify other possible cosmic messengers emitted by it . “
” The gravitational wave observations, integrated with the possible identification of additional radiation emitted from their source , – says Marco Pallavicini , president of the INFN National Commission for astroparticle physics research – is like if they gave us a whole new way with which to explore our universe ” . “ No one can say what we will discover with this new sensory tool, but history teaches that we expect many surprises ,” says Pallavicini.
Next the second signal of gravitational waves was probably observed a third event, considered very likely but still awaiting confirmation. “it’s a much weaker event and had been identified in the first month of analysis data “ when ” could very well be a fluctuation of two detectors “, added Ricci referring to the American LIGO detector (Large Laser Interferometer gravitational-Wave Observatory) , “but many are willing to bet on a gravitational event”
VIRGO and national collaboration
Italy has played a major role in achieving these fundamental results and it will continue with its commitment to providing crucial contributions. INFN, together with the Centre National Recherche Scientifique of the French CNRS, initiated the project to the Virgo interferometer, in Cascina (PI) at the European Gravitational Observatory EGO, who manages it, where the physics community INFN is now strongly engaged in this research. VIRGO is a project born from the original idea Adalberto Giazotto Italian and French Alain Brillet. They work together 250 physicists and engineers, of which half of the INFN, from 19 institutes in Italy (INFN), France (CNRS), the Netherlands (Nikhef), Hungary (MTA Wigner RCP) and Poland (POLGRAW group). INFN participates in VIRGO with their own sections at the Universities of Pisa, Florence with the research group of Urbino, Perugia, Genoa, Rome Sapienza, Rome Tor Vergata, Naples, Padua, and the National Centers Tifpa of Trento and of GSSI ‘ Aquila.
LIGO
The LIGO observatories , funded by the National Science Foundation NSF, have been designed and are now operated by Caltech and MIT. at the LIGO scientific collaboration participating collaboration GEO600, which is part of the eponymous observatory in Germany, and the Australian Consortium for Interferometric Gravitational Astronomy, as well at US research universities and institutes and 14 other countries.
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