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Gravitational waves: tightening the circle


It is more of a hope, is almost a promise. INAF two astronomers, who study the elusive radiation predicted by the theory of general relativity of Einstein, explain why they are confident that it will be soon revealed the signal. Thanks to Planck and interferometers new generation, on Earth and in space
“The take.” Luigi Stella, astronomer ordinary INAF Astronomical Observatory of Rome has no doubts. “Gravitational waves have its day.” For 50 years, scientists are hunting without success to this elusive radiation, planned in 1916 by the theory of general relativity Albert Einsten, but never directly observed. “It is different from those electromagnetic waves; are generated by large masses of matter that undergo strong acceleration, “says Stella. “We have long known that exist by virtue of a series of indirect observations that confirm the precise predictions of Einstein’s theory. We were never able to grab them directly, but they are there, and soon we will be able to intercept them. ”

Atom Interferometry for Detection of Gravitational Waves

onde-gravitazionaliCredit: NASA

The search for gravitational waves – ripples in space-time that propagate at the speed of light and matter moving imperceptibly, like a boat that moves on the water’s surface – could be close to a turning point. On them hangs a “arrest warrant” international and scientists around the world have joined together to ciccare not the target.
Unleashed in the footsteps of gravitational waves (among other things) is the European Space Agency’s Planck satellite, true pride for the Italian scientific research that has created one of the two spectrometers on board, LFI (the other is HIFI) under the leadership of N. Mandolesi INAF-IASF Bologna. Well, as confirmed by a recent review in the prestigious journal Science, just Planck observatory, launched in 2009 to trace the dawn of time, has placed the utmost confidence in the near future to detect traces of primordial gravitational waves, ie those generated by big bang, the creation of the Universe: The big Bang.
The population of a second, the Universe has grown from a small dot on a huge bubble, 10 ^ 26 times larger. “By studying the cosmic microwave background radiation with the unparalleled sensitivity of Planck satellite should be able to find traces of gravitational waves generated by the incredible acceleration of matter. It would be a big blow to test the theory of inflation and have valuable information on the first beats of the life of the Universe, “says Gianfranco De Zotti, astronomer professor at the INAF-Osservatorio Astronomico di Padova, the Italian collaboration on the Planck satellite.
If it is already very complex detect gravitational waves emitted by two neutron stars, supernovae, magnetar and blacks holes, let alone as an undertaking to the extent possible both harness the primordial gravitational waves. “There are not perceptible by the instruments normally involved with the study of this radiation, are very low frequency waves with wavelengths of cosmic dimensions. Planck could detect the weak signal by measuring the perturbations of the polarization of the cosmic background, “says De Zotti. Not that he does it, but it sure will do much better than has been possible to do so far. “If Planck had to miss the target, it will be helpful to set upper limits more stringent for satellites that will be.”
In parallel, it sifts the nearby universe. “They are already operating two instruments can reveal the weak signals produced by the passage of a wave gravitation: VIRGO located in the countryside of Pisa, and LIGO, consisting of two stations in the US,” Stella resumes. “It is interferometers, with arms kilometric where they run hundreds of times laser beams reflected by a system of mirrors. They are capable of recording the passage of gravitational signals coming from distances up to about 50 million light years. However, within this range of coverage, the passage of a gravitational wave is a rare occurrence, one every 10-100 years. ”
But this scenario is about to change. “Before 2020 – continues astronomer OA Rome – we have the interferometers LIGO and VIRGO second generation. These new tools will allow to sink look much further in the Universe and disclose annually the signals of many sources of gravitational waves of high frequency, such as neutron stars orbiting very close before merging with each other, explosions supernovae or very rapidly rotating magnetar. A few years later, LISA, a spatial interferometer result of collaboration between ESA and NASA will reveal the collisions of supermassive holes blacks. In fact, it will open an exciting new chapter in astrophysics of the twenty-first century, and in the study of gravitation. ”
Italy, with the INAF, INFN and universities, is the game that, hopefully, will close in the next few years. “Our country has a long tradition in this field of research, since the days of Edoardo Amaldi. The contribution astrophysicist is critical to confirm and interpret the phenomena revealed by interferometers, through observations with the most powerful telescopes on Earth and in space. ”
But why gravitational waves are so important? “It is one of the fundamental aspects of modern physics and remains to be confirmed with the experimental verification: the litmus test that we follow for half a century,” explains Stella. “Not only. Be able to directly observe these perturbations of space-time would give us the key to access to information currently off limits and the study of extraordinary phenomena and so far unfathomable. “

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