With the announcement, on 11 February 2016, of the first detection ever of a gravitational wave by the LIGO and Virgo Collaborations, a New Astronomy, based on listening to the space-time vibrations, was born.
This long-awaited wave, 100 years after the theoretical prediction by Albert Einstein and 50 years after the first experimental efforts, arrived on Earth on 14 September 2015 and was finally perceived by humans with very smart “microphones”.
It originated more than one billion years ago, when two black holes of 29 and 36 solar masses began the final phase of their spiralling in towards each other until they merged, colliding at the incredibly high velocity of almost half the speed of light, giving rise to a single black hole with a mass almost 62 times the solar one. The three solar masses missing from the total mass balance correspond to the energy emitted out of the merging in the form of gravitational waves.
The Universe has carried this ripple uncorrupted at the speed of light, with its information on the nature, masses and spins of the two fantastic parent objects and of their final product, down to our planet Earth, to be caught by the two detectors of the Laser Interferometer Gravitational Observatory [LIGO].
These instruments, which are located in the US, one in Washington State and the other in Louisiana, are very sophisticated laser interferometers, and together with Virgo, which is located in Italy, nearby Pisa (IT), and Geo, located near Hannover (DE), make a network of detectors built and operated by two international scientific collaborations working in perfect harmony.
Europe has always been in the frontline of gravitational wave research, from the old resonant detectors to the new laser interferometers. European physicists have made important contributions to LIGO and were essential in developing and building Virgo. These are currently the most advanced detectors and will both start new observations next summer, perhaps obtaining unforeseen results, as appropriate for a newly born Astronomy.
Did it take too long? Well, gravitation is the weakest among the fundamental interactions, and the activity of gravitational waves hunters should be considered in the light of the ultimate smallness of the effects to be measured. It has not been easy to finally observe vibrations of amplitudes smaller than one billionth of a billionth of a meter as they succeeded to do.
In this respect, the phrase by Kip Thorne is quite à propos: “Gravitation: A theorist’s Paradise and an experimentalist’s Hell”.
Hell is now over, let’s welcome Paradise.
University of Rome “Tor Vergata” and
INFN Gran Sasso Science Institute
- The Gravitational Wave International Committee: https://gwic.ligo.org/