This same week, the LIGO experiment detected a gravitational wave for the second time. Although it is an epic event, it is no longer so new and it will be less and less, as more and more stellar events are perceived by the Hanford (Washington) and Livingston (Louisiana) interferometers.
But let’s get to the important thing. What differences and coincidences are there between this new event (called GW151226) and the first and revealing one that made so many headlines (dubbed GW150914)?
Comparing both events
1. Both are events that occurred in 2015; however, its public exposure was made months later, already in 2016. GW150914 took place in September 2015 and was announced with full fanfare in February 2016. GW151226 occurred on December 26, 2015 and has been revealed to humanity in June 2016 (almost 6 months later). The reason for so much mystery and delay in the announcements is that in both cases an intense checking process has been necessary to eliminate all sources of error and uncertainty. In the United Kingdom and other countries, December 26 is known as “packing day”, since it is when they give gifts to the most disadvantaged for Christmas; hence, GW151226 has also received the alias “pack day event”.
2. In this case, wave GW151226 reached both detectors almost at the same time, so cosmologists can say that the propagation has reached our planet just “above” or “below” the fictitious line formed by the two LIGO detectors (about 3,000 km apart). That is, the gravitational wave came “from the sky” or “from the antipodes.” The GW150914 signal reached Earth “from the side”, so the Louisiana detector perceived it earlier (a few thousandths of a second) than Washington’s. We remember that gravitational waves propagate, just as Einstein predicted, at the speed of light.
3. Again it is about two black holes colliding, but smaller than those corresponding to the September 2015 event. The signal is therefore smaller; however, with a higher frequency that LIGO is better suited for. Of course, it has been necessary a colossal work of statistics and data mining.
4. The results obtained fit the fact that one of the black holes was spinning like a top, which suggests that it swallowed a companion star (or part of it) before colliding with the other black hole.
What if. This astronomical event GW151226 is also translatable into sound (as was already GW150914). You can listen to it from here.
Finally, we remember that LIGO has Spanish “blood”. The LIGO-Virgo working group is co-chaired by Dr. Alicia Sintes, from the University of the Balearic Islands and a fascinating group of Spanish scientists works with her.
Alberto Corbi is a professor at the Higher School of Engineering and Technology (ESIT) of the International University of La Rioja (UNIR).
