As predicted by the LIGO experiment itself, we will continue (and have continued) to detect collisions of super massive objects. And so it has happened again: on September 27, 2017, the aforementioned scientific collaboration confirmed the fourth detection of gravitational waves . As on other occasions it has been about two stellar-size black holes (those whose mass is in the range of tens of masses of our beloved Sun). However, before continuing, it is worth highlighting the following unprecedented fact in the history of gravitational wave detection and, by extension, in the history of science.
And the fact is none other than the present discovery is the first made with three different interferometers and corresponding to two related but independent institutions . We are referring, on the one hand and of course, to the already known LIGO and on the other, to the “new boy in the city of gravitational waves”: the Virgo experiment , led by the European Gravitational Observatory (EGO) institution.
The three detectors to which we are referring are, on the one hand, the already familiar ones located in Hanford and Livingston (those attached to LIGO), and on the other hand, the one belonging to EGO / Virgo and which is located near the romantic city from Pisa (Italy). The latter had been in operation for just two weeks before the detection, with which it can be concluded that its intervention in the history of General Relativity is being a resounding success and that it has started off on the right foot. The three interferometers form a triangle on the surface of the Earth whose sides measure about 4 thousand (Livingston – Hanford distance), 8 thousand (Livingston – Pisa) and 9 thousand kilometers (Hanford – Pisa), respectively.
Like the three previous events related to the detection of gravitational waves (GW150914, GW151226 and GW170104), this has been baptized with a name that refers to the date of detection: GW170814. In other words, the deformation of space-time reached the Earth in the middle of last August . Although many of us were on vacation, the Universe doesn’t know what it’s like to take a break, and neither does the LIGO and Virgo experiments.
Comparing the timing of the gravitational wave detections at the three observatories allowed astronomers to vastly improve the location of the signal origin in the sky.
In this case, the event corresponds to the merger of two black holes of 31 and 25 solar masses , respectively. Both cosmological monsters danced to their union for brief seconds almost two billion light-years away from our current position in the cosmos.
The black hole “son” happened to have 53 solar masses . What has happened to the 3 missing solar masses? For it is precisely this mass defect that was transformed into pure gravitational energy. It is this wave energy that, gently warping space-time, caressed our planet a few weeks ago while many of us were, surely, taking a bath on the beach, enjoying a well-deserved summer walk or having an ice cream on a boardwalk.
What are the advantages of adding Virgo, the third detector, to LIGO?
Many, but suffice it to say that the volume of sky in which the collision occurred can now be determined with much more precision (specifically, 20 times better).
The area of the sky now occupies only about 60 square degrees (to give us an idea, the full moon represents 1/5 of these units). With this new ability to limit the area of origin, we can now point other telescopes more quickly and try to hunt traces of this and other events that were (and will be) emitted as electromagnetic waves (light, radio, X-rays, etc.).
Unfortunately this will be complicated, since black holes do not emit light (not even during their fierce merger), but … what less than trying! The positive thing is that now we can do it more efficiently thanks to the good work between the three detectors, but above all, thanks to the good disposition of all the countries and institutions involved. And this has done nothing but begin. New interferometers and observatories on the ground and in space will soon join this “brotherhood of gravitational wave hunters”.
Image: NASA
Alberto Corbi is a professor at the Higher School of Engineering and Technology (ESIT) of the International University of La Rioja (UNIR).
