A decade of discovery: Academics celebrate 10 years since the first detection of gravitational waves amid announcement of exciting new breakthrough
10 September 2025
Scientists at Cardiff University are reflecting on the significance of the first-ever detection of gravitational waves, ten years on.
The signal, picked up by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) on Monday 14 September 2015, carried with it information about a pair of remote black holes that had spiralled together and merged.
It had travelled about 1.3 billion years at the speed of light – but was not made of light. It was a different kind of signal: a quivering of space-time called gravitational waves first predicted by Albert Einstein 100 years prior.
Emitted as a result of violent cosmic events, such as exploding stars and merging black holes, gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained.
The historic discovery meant researchers could now study the universe in three different ways.
Light waves, such as X-rays, optical, radio, and other wavelengths of light as well as high-energy particles called cosmic rays and neutrinos had been captured before, but this was the first time researchers had witnessed a cosmic event through its gravitational warping of space-time.
Research undertaken at Cardiff University laid the foundations for how gravitational waves are detected, with the development of novel algorithms and software that are now standard search tools for detecting the elusive signals.
The team at the Gravity Exploration Institute (GEI) also pioneered the data-analysis methods used to detect the signal and led the development of the signal models that were used to measure the properties of the signal, including how massive the black holes were, and the distance of the source.
The latest breakthrough announced today, which tests an idea put forth by Stephen Hawking in 1971, would not have been possible without the past 10 years of developments; scientists have now been able to “hear” two black holes growing as they merged into one, in accordance with Hawking's theorem.
Professor Mark Hannam, Director of the GEI, recalls the first detection: “I didn’t believe the detection at first, and it wasn’t until several weeks later that I was convinced, so the reality of it grew on me slowly.”
The first time the enormity of it hit me was when someone showed me a picture of the signal in the data. By that time, I had been running simulations for over a decade, and I was very familiar with what binary black holes signals look like. When I saw the plot of the data my first thought was, ‘wow, that’s a really bad simulation’, and then it struck me that I wasn’t looking at a simulation – it was an actual signal produced by nature.
Ten years on, LIGO is routinely observing roughly one black hole merger every three days and operates in coordination with two international partners, the Virgo gravitational-wave detector in Italy and KAGRA in Japan.
Together, the gravitational-wave-hunting network, known as the LVK (LIGO, Virgo, KAGRA), has captured a total of about 300 black hole mergers.
During the network’s current science run, O4, the LVK has discovered about 220 candidate black hole mergers, more than double the number caught in the first three runs.
LIGO Scientific Collaboration (LSC) spokesperson Professor Stephen Fairhurst from Cardiff University was among those to report on the very first detection in 2015.
He said: “A decade ago we couldn’t be certain that black holes ever collide in our universe. Now we observe several black-hole mergers per week.”
With the three hundred gravitational-wave candidates observed to date, we’re beginning to provide a census of the population of black holes in the universe. We’ve already found several surprises, including black holes which are less massive than expected – about four times the mass of the sun; and also, some that are more massive than anticipated – over 100 times the mass of the sun.
Gravity Exploration Institute
“As a PhD student, my research focused on the mathematical properties of black holes and their horizons. I wouldn’t have dreamed that we would ever be able to measure those properties in nature. Now, I’m honoured to serve as spokesperson of the LSC as we do exactly that.”
The dramatic rise in the number of LVK discoveries over the past decade is owed to several improvements to their detectors – some of which involve cutting-edge quantum precision engineering.
LIGO remains by far the most precise ruler for making measurements ever created by humans.
The space-time distortions induced by gravitational waves are incredibly miniscule. To sense them, LIGO must detect changes in space-time smaller than 1/10,000 the width of a proton – 700 trillion times smaller than the width of a human hair.
Professor Hartmut Grote, who joined Cardiff in 2018 to start a new experimental research group, explained: “The LIGO detectors have been enhanced during the O4 run with electronics built in Cardiff, which contributed to achieving higher sensitivity than in previous runs.”
It's exciting that technology developed in Cardiff is having a direct impact on how we hear and understand the universe.
LIGO's improved sensitivity is demonstrated in a recent discovery of a black hole merger referred to as GW250114 after the date the signal arrived at Earth.
The event was not dissimilar to LIGO's first-ever detection, GW150914, but 10 years of technological advances reducing instrumental noise means the GW250114 signal is dramatically clearer.
The sources of GW250114 and GW150914 were almost the same, and the clarity with which we observe GW250114 provides a dramatic demonstration of the remarkable improvement in LIGO detector sensitivity over the last 10 years. Previously we were excited to find the black holes, now we are beginning to probe their fundamental properties.
By analysing the frequencies of gravitational waves emitted by the merger, the LVK team was able to provide the best observational evidence captured to date for what is known as the black hole area theorem.
The idea, put forth by Stephen Hawking in 1971, says the total surface areas of black holes cannot decrease.
The LIGO detection allowed the team to "hear" two black holes growing as they merged into one, verifying Hawking's theorem.
Professor Hannam added: “The current detections – in particular the latest signal, GW250114 – illustrate what we will be seeing in the next few years: hundreds more signals, and some signals strong enough for us to do increasingly precision measurements and tests of black-hole properties.”
It’s going to be a race for our analyses to keep up with the increasing sensitivity of the detectors to, ultimately, untangle the astrophysics of black holes in the universe.
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