The Detection of Gravitational Waves, a year on

It’s one year since the LIGO collaboration (LSC) announced the first direct detection of gravitational waves. On that day last February, I remembered being very excited. We’d been sworn to secrecy for months, coached on where to send questions from journalists and what not to put on social media. While we knew there was still a very, very slim chance that the detection might not be real (only those at the very top of the collaboration had full confirmation that the signal was real and not a blind injection) we also knew that there was champagne chilling in the fridge and that a lot of press were around at the announcement.

At the University of Glasgow, approximately 70 people are active researchers in the IGR – the Institute for Gravitational Research, including me. That’s a pretty massive research group but it’s not the biggest, Germany’s AEI is larger and there are other large groups in the US. Still, 70-ish people packed in a room waiting to hear the news is enough for a real party. When they made the announcement that we’d finally detected gravitational wave from a pair of colliding black holes the room erupted. I’m not sure how long we cheered for but I remember hugging everyone within reach before being pushed towards a champagne table.

An artist’s impression of two massive bodies colliding and the gravitational waves they create. Image credit: NASA

Of course, by this time, the LIGO detectors had already picked up two more candidate events – one of which was eventually discarded as the signal wasn’t quite strong enough to be absolutely sure. There would be an announcement later in the year about the second one. With these detections, we learned so many things. We learned that gravitational waves exist and general relativity is doing just fine, we learned that black holes exist, that they collide, that they collide in less time than the age of the universe and that they can somehow get to ~30 solar masses before they do it. As had always been poetically predicted by gravitational waves researchers – detecting gravitational waves had opened a new window on the Universe.

In the following weeks and months upgrades were carried out on the Advanced LIGO detectors to prepare them for O2 – the second observing run that began in November. Meanwhile, I worked on my PhD thesis and largely fell out of the loop in terms of new research. I got a new job within the IGR, moving from materials for gravitational wave detectors to a new kind of detector – a small, sensitive detector for picking up changes in gravitational field caused by objects of different masses underground. I’m still in the LSC, but unless I move back to gravitational wave detectors at some point, my membership will eventually lapse.

Of course, while I was buried deep in thesis work and getting to grips with a slightly different research area, the world was not ignoring that initial detection. It seemed like every few weeks another email would come through informing us that the LSC had been recognised by this scientific organisation or that one. The list of prizes won by the collaboration, or by those running it, grew and grew. Many of us held our breath when the day for announcing Nobel Prizes came around, but the Nobel committee are not known for disregarding their own rules, and the detection had arrived too late for 2016 nomination. Maybe it’ll happen this year.

My breakthrough prize medal. “Scientists changing the world”

The 2016 Breakthrough Prize for physics went to the LSC for the detection of gravitational waves and, uniquely, the prize committee decided that the entire collaboration should benefit. I received my Breakthrough Prize medal (and a snazzy lapel pin) through the post only a couple of weeks ago. Physics World, a news organisation run by the Institute of Physics, announced that the detection of Gravitational Waves was its breakthrough of the year – the MEMS gravimeter that I was now working on also made the top ten, putting me in the strange position of having worked on 20% of the greatest breakthroughs in 2016 – at least according to the IOP. As far as I’m aware, the only other person who can claim that is my PI, Prof Hammond.

While we wait to see what will be detected by this second observing run I think it’s worth reflecting on how spectacular those first detections were. Some people in the collaboration had been working in the field for their entire careers, continuously improving the sensitivity of the detectors and never quite 100% sure that they’d find anything. A full century passed between Einstein setting down his theory of general relativity and Advanced LIGO detecting colliding black holes through their gravitational radiation. So, here’s a few more astonishing statistics:

  • The Advanced LIGO detectors were ready just in time to detect the waves – they picked them up during the first day of observing…
  • …but the black holes merged more than 1 billion years ago
  • They were travelling at 0.6 times the speed of light when they collided
  • The collision was 500 billion times brighter in gravitational radiation than our entire galaxy in electromagnetic radiation
  • In 0.2 seconds, 3 times the mass of the Sun was turned into gravitational radiation
  • All of this is apparently perfectly normal

One year on that first detection is still as incredible to me as it was on the day we first thought we’d found something, and just as incredible as it was when it was announced that we were correct. As we said at the time, though, this is just the beginning. The next steps are to improve sensitivity, to develop the global network of detectors and to start using gravitational waves to do real astronomy, just like we do with traditional telescopes. I can’t wait to see what the next few years will bring.

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