Over the weekend in Maryland, physicists involved in the Virgo and LIGO project made the exciting announcement that they had discovered four completely new black hole mergers which came about after gravitational waves were detected around these black holes. This includes what is thought to be the largest black hole collision that we currently know about, which occurred a whopping 5 billion years ago. This monstrous collision created a black hole so big that it is 80 times larger than the sun.
As Ars Technica reports, the four new black hole mergers that have been discovered will be included in a very special piece of research known as the Gravitational Wave Transient Catalog, or GWTC-1, whose aim will be to report on gravitational wave events like these and document them thoroughly. Including the four new black hole mergers that were just detected, there will now be 11 gravitational wave events to catalog.
To detect gravitational waves, LIGO utilizes laser interferometry, which means that lasers look at the very small changes that occur in two objects which are scattered extremely far apart and then measures these. At the moment, LIGO uses detectors that are based in Louisiana and Washington, and as of 2016 also began using the Advanced VIRGO detector in Italy.
There have now been 10 mergers of binary black holes observed by LIGO and Virgo instruments. Some of these black holes have been reported to be 50-34 times bigger than the sun! The latest merging is the most powerful to date. https://t.co/QriCwYxoDd— Black Hole News Network (@AstronomyProp) December 4, 2018
On September 14, 2015, physicists noticed that detectors had picked up signals from the merger of two black holes that sent shockwaves rippling through space and time. Two further black hole mergers were later picked up from this date and run, along with a second run that took place in 2017. If you’re wondering why this is the first you have heard about the detection of these black hole mergers through gravitational waves, it is because physicists wanted to make absolutely certain that their data was correct.
As Northwestern University physicist Shane Larsen explained, “We’ve been sifting through the data, looking at every feature, comparing it to our astrophysical predictions, cross-checking it against monitors that tell us the health of the instruments, determining if it appears in all the detectors, and using our most robust (but slow-running) super-computer analysis codes. Having a collection of events is how we learn things about the Universe that can’t be learned from just a few observations.”
The black holes that were discovered are known as GW170729, GW170809, GW170818, and GW170823, and as LIGO and Virgo will start a third run sometime next spring, there may be even more to add to the gravitational wave catalog very soon, although the discovery of four new black hole mergers is certainly thrilling in and of itself.