Signals from the cosmos: gravitational waves
Gravitational waves
The theory of relativity, which has received numerous confirmations
from astronomical measurements, predicts the existence of gravitational
waves produced by masses undergoing acceleration. The signal
of a gravitational wave is, however, very small, and can be
detected only if the wave was produced by an event of enormous
intensity, such as the explosion of a supernova or the final
phase of a binary system of massive stars. Gravitational waves
can be observed using optical interferometry or resonant bars.
In each of these experimental approaches, Italian physics occupies
a high-profile position.
Near Pisa, a large laser interferometer, VIRGO, is under construction.
VIRGO, which is the product of Italian and French collaboration,
has two orthogonal arms each three-kilometers long, and makes
use of equipment with exceptional optical and mechanical characteristics,
which allows for absolute isolation from the surrounding environment.
VIRGO will be able to detect gravitational radiation produced
in cosmic phenomena such as the impact between two compact stars
in a binary system within the Milky Way or in external galaxies
within a radius of about 300 million light-years. The facility
will begin operations in 2002 and will be under the management
of the EGO consortium.
Other interferometers are in various phases of construction
in the U.S.A., Germany, and Japan. There are currently five
resonant bars in operation in the world—in the U.S.A.,
Italy, Switzerland, and Australia.
Two ultracryogenic bars, NAUTILUS and AURIGA, are in operation
at the Frascati and Legnaro Laboratories, respectively, and
work in concert with high efficiency. Significant developments
in cryogenics and superconductive technologies were required
for their construction. The widespread distribution of resonant
bars over the surface of the planet has given rise to a global
network which operates as a single observatory, IGEC. The simultaneous
observation of gravitational waves by more than one detector
would not only allow for security in the confirmation of the
signal, but would also allow its properties to be measured.
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