Paolo Cavallo wrote:
> "Elio Fabri" <mc8827_at_mclink.it> ha scritto nel messaggio
> news:bjnstt$134h$5_at_newsreader2.mclink.it...
>
>
>>Tanto per fare un esempio, la famosa binaria di neutroni nella quale
>>sono state viste per la prima volta le onde gravitazionali...
>
>
> Davvero? Le hanno viste, finalmente? Mi � sfuggito completamente,
> puoi darmi dei riferimenti?
>
> Grazie,
>
> Paolo Cavallo
No non le hanno viste direttamente nei primi '90: in ogni caso
Hulse e Taylor hanno preso il Nobel nel '93.
Guarda direttamente su
http://www.math.ucr.edu/home/baez/RelWWW/tests.html
ti riporto i punti salienti
(...)
Since their discovery, it has been recognized that neutron stars provide
extraordinary laboratories for testing theories of gravitation, because
their surface radius is typical only two or three times their
Schwarzschild radius. Thus, tremendous excitement was generated by the
discovery in 1974 by Taylor and Hulse of the first known binary pulsar,
PSR1913+16. (Several others have since been discovered.) This binary
star system consists of two neutron stars of nearly equal masses (about
1.4 solar masses each) which orbit around each other with a period of
only 7.75 hours. The orbit is highly elliptical, with distances ranging
between about 1 and 5 solar radii.
(...)
But the importance of Taylor's continuing observations of PSR1913+16
goes far beyond confirming the prediction of the emission of
gravitational radiation at the rate predicted by gtr, because (as was
noted above) many scalar-tensor theories of gravitation which mimic gtr
in the weak-field slow-motion regime (i.e. have PPN parameters almost
identical to the PPN parameters of gtr) give very different predictions
from gtr in the strong field regime. In particular, most of these
theories predict so-called dipole gravitational radiation, which would
be very strong in the case of binary pulsars, resulting in a very rapid
speedup of the orbital period, whereas according to gtr, dipole
gravitational radiation does not exist--- the strongest radiation coming
from a binary pulsar should be the so-called quadrupole radiation, which
is far weaker. Thus, observations of binary pulsars such as PSR1913+16
and PSR1534+12, have already ruled out many theories which could not
possibly have been ruled out by solar system observati
(...)
The 1993 Nobel Prize in Physics was awarded to Hulse and Taylor for
their discovery of PSR1913+16.
ciao, Valter
------------------------------------------------
Valter Moretti
Faculty of Science
Department of Mathematics
University of Trento
Italy
http://www.science.unitn.it/~moretti/homeE.html
Received on Sat Sep 13 2003 - 12:55:49 CEST