Free Astronomy Magazine January-February 2016

ASTRONAUTICS of General Relativity, which predicted their existence, as well as the existence of many other phenomena vir- tually unknown at the time. In the last 100 years, scientists have tried to demonstrate from the ground the existence of gravita- tional waves by devis- ing various experiments (the best known being the Laser Interferome- ter Gravitational-Wave Observatory and the Virgo Interferometer), without ever obtaining convincing results. But why is it so difficult to ascertain through ob- servations a phenom- enon whose existence was theoretically predicted already a cen- tury ago? The answer is in the nature of gravitational waves. Their origin and prop- agation are totally different from those of the much more familiar electromagnetic waves that so far have enabled us to dis- cover almost everything we know of the universe. Gravitational waves are, by defi- nition, generated by “accelerated masses”. It is the case of the merger of supermas- sive black holes, of the explosion of super- novae, of close binary systems of collaps- ing stars, but also of fast-forming galaxies. T he liftoff of the VEGA VV06 rocket from the European spaceport the French Guiana, carrying onboard the LISA Pathfind- er probe. [ESA– Stephane Corvaja] Bottom left, a video showing the structure and operation of the LISA Pathfinder probe. [ESA/ATG medialab] These would be, in theory, some of the sce- narios in which the more energetic gravita- tional waves are produced. Each of those sources would irradiate the cosmos of waves as fast as the light, having different charac- teristics depending on the mechanism of production and full of information about the processes from which they sprang. Succeeding to “observe” them would mean being able to investigate phenomena that today are inaccessible to any type of tele- scope in any band of the electromagnetic spectrum. In order to succeed we must, how- ever, overcome some obsta- cles that seem insurmount- able, such as the fact that a gravitational wave moves in space-time by contracting and expanding it with its passing, which means that also the instruments used for its detection jointly contract and expand with space-time. This makes it extremely diffi- cult to measure waves, which even if they can reach mil- lions of kilometres in length, their height is insignificant,