Gravitational waves

 

Gravitational waves (g.w.) are predicted by General Relativity. They are generated by accelerated motion of bodies, which must have quadrupolar or higher order symmetry. Detectable signals are expected only by massive, compact celestial bodies as for instance two neutron stars or black holes in orbit in a binary system or vibration of black holes and neutron stars. For a description of gravitational wave sources of interest for AURIGA please follow this link.

Up to now the only observational evidence is their emission by binary systems. The first studied was the PSR1913+16 which is formed by two neutron stars: R. Hulse and J. Taylor were able to measure with unprecedent accuracy its orbital parameters and found that the two bodies are spiralling one into the other as they lose energy by emission of gravitational waves. These measurements are in excellent agreement with the prediction of General Relativity; R. Hulse and J. Taylor were awarded the Nobel prize in 1993 for this research.

Gravitational waves can be viewed as ripples  of the space-time. They occur in two fundamental states of polarization, usually known as 'cross' and 'plus'. The effect on matter of the passage of gravitational radiation is a squeezing and stretching, depending on the phase of the wave. For instance the effect on a ring of test masses is shown in fig. 1, in the reference frame that is in free fall with the center of mass. The upper raw refers to the plus polarization while the second to the cross polarization; the ring is deformed by the wave and the effect is shown at different phases.

ring of test masses

The effect of the passage of gravitational radiation through a person is sketched in fig.2: well, the effect of squeezing and stretching has been exaggerated a bit!

wave on the person

Please, follow this link for a description of gravitational wave sources of interest for AURIGA .


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