On Thursday, June 1, 2017, the third great detection of gravitational waves by the LIGO project was announced. Again it seems to be the merger of two black holes whose combined mass is almost 50 times that of our beloved Sun and about 200 km in diameter. Specifically, the largest of them had 32 solar masses (and 190 km wide) and the smallest, 19 (and 115 km from end to end). The two “excess” solar masses were converted almost instantaneously into pure energy at the time of fusion, which has traveled in the form of a gravitational wave to our little and beloved planet Earth, where LIGO has detected it thanks to its two observatories in Hanford (Washington state) and Livingston (Louisiana state).
A detection that occurs for the third time, and that does nothing but confirm the estimates of the most important scientist of the 20th century, Albert Einsten , and that confirms one of the foundations of modern physics, the Theory of Relativity. A scientific milestone relevant enough to earn its discoverers the 2017 Princess of Asturias Award for Scientific Research.
As with every detection, this one actually occurred many months ago and has not been announced until the detected event has been fully verified. Specifically, the event took place on January 4, 2017. That is, it was not until five months later that the LIGO collaboration (also made up of the Relativity and Gravitation Group of the University of the Balearic Islands) has decided to make the results public . Normally, this type of extreme science news is not transmitted to the daily press until a communication has previously been made in a scientific journal , and this has also been the case this time. Communication in a journal of this type is not only the appropriate way for a publication of this genre. Furthermore, the peer review normally used by these publications guarantees the quality of the work and the scientific results.
This third dance of black holes took place at a distance of 3 billion light years , which can be said that, compared to the two preceding detections, it is the most distant to date . The place in the sky where this fusion took place cannot be precisely delimited, but when the Virgo sensor is activated in Europe, this limitation will change substantially: we will not only know the distance to the event that takes place, but also its approximate region in the celestial vault.
Detection occurred in the following manner . At two in the morning on January 4, the arms of the LIGO laboratory in Handford shook. When we say that they “trembled”, we are referring to sub-micrometric changes in their length, which can only be detected by variations in the time it takes for light to travel these arms. Specifically, this oscillation was, in amplitude, 1000 times smaller than the diameter of a proton in the nucleus of any atom (also called an attometer). LIGO’s resolvability was already impressive, but after the latest enhancements, even more so. Like the Large Hadron Collider experiments and detectors (Atlas, CMS, LHCb, etc.), LIGO interferometers receive polishing and fine-tuning every so often before starting a new run or data collection stage.
About 3 milliseconds after Handford stirred on January 4, Livingston’s interferometer underwent a similar micro-shake and with the same time pattern, nanosecond by nanosecond. This precise delay and great similarity between observations helps to endorse the nature of the event, since it cannot be anything other than something that propagates at the speed of light . About 3 milliseconds is exactly the time it would take for an object traveling at this speed and moving from the LIGO observatory in Hanford to the corresponding one in Livingston. In this case, the traveling object is nothing other than the trace of beauty, and fierceness, of the universe on our beloved planet and its inhabitants.
In summary, we have the third confirmation of the existence of gravitational waves and of Einstein’s Theory of General Relativity . And, its discoverers, a deserved scientific recognition of the stature of its contribution to physics.
Alberto Corbi is a professor at the Higher School of Engineering and Technology (ESIT) of the International University of La Rioja (UNIR).
Imagen: R. Hurt/Caltech-JPL
