order to better understand the universe and its evolution, one needs to be able
to interpret all the messages received from the outer space.
Electromagnetic radiations, by far the main astronomical observational mean,
are generated by the excitation of atomic particles. On the contrary, gravitational
waves have a totally different nature, being generated by the motion and variations
of masses of celestial bodies. In a way, todays astronomical observation
is like watching a concert on TV with the volume completely turned off. Detecting
gravitational waves may be compared to turning on the volume and listening to
something never heard before.
The observation of gravitational waves will therefore significantly complement
the observation of electromagnetic waves (light, radio, micro-waves, X and gamma
rays) and of astro-particles (cosmic rays, neutrinos). It will reveal aspects
of the Universe not reachable by these means and will extend the observable
domain even in the cosmic zones darkened by dust and masked by other phenomena.
The most dramatic processes of the cosmos such as supernova explosions, catastrophic
collisions, fusion of binary systems, rotation of pulsars, interaction of black-holes
or the original big-bang generate gravitational waves. Observing gravitational
waves emitted during these violent processes is the only way to obtain information
on the masses involved.
The total mass of the universe, evaluated from the mass of observable bodies,
cosmic dust and gases, is less than 10% of the mass necessary to explain the
motion of the galaxies. Because gravitational waves are generated by the motion
of large masses, their observation is likely to provide fundamental information
on this puzzling problem.
Every new instrument to observe nature has permitted unforeseen discoveries,
which have enriched our knowledge and often revolutionized our image of the
world. Gravitational wave detectors are likely to reveal unsuspected aspects
of the Universe.
Another aspect to be considered is that, unlike telescopes, which can only look
at a very small portion of the sky at a time, gravitational waves detectors
are by nature non-directional, they are constantly listening to
the whole Universe. This gives the possibility to observe cataclysmic phenomenon
such as the explosion of supernovas from the very first moment whereas they
are usually discovered by telescopes well after the crucial moment.
a new window on the Universe
- VLT picture NGC 1232