The violent event, detected on 14 January this year, took place 1.3 billion light years from Earth. When the two black holes, each 30 to 40 times the mass of our sun, spiralled into one another, they merged to form a single, larger black hole and sent out ripples through space-time known as gravitational waves.
By measuring the surface area of each original black hole and comparing it with the final product, scientists confirmed Hawking’s 1971 theory that black holes can only grow, never shrink. The original pair covered about 240,000 square kilometres combined – a little larger than Victoria. The newly formed black hole measured roughly 400,000 square kilometres or about half the size of NSW.
“This is the best evidence yet that Hawking was right,” said Neil Lu, a PhD researcher at ANU’s Centre for Gravitational Astrophysics. “The final black hole is bigger than the sum of the two originals. By listening to its vibrations, we picked up the cleanest black hole ‘note’ ever recorded – multiple tones exactly matching Einstein’s predictions.”
Dr Ling Sun, who led ANU’s analysis team, said the discovery showed the strange simplicity of these cosmic giants. “They’re defined only by mass and spin, yet their horizons grow in a way that encodes the disorder of the universe.”
Distinguished Professor Susan Scott, who leads gravitational wave data analysis at ANU, added: “Black holes aren’t stars – they’re geometric objects in space. This confirms two key features: they can only get bigger, and they ring like a bell when disturbed.”
The breakthrough caps decades of work by the global LVK Collaboration (LIGO, Virgo, KAGRA), which has fine-tuned instruments capable of detecting distortions in space-time smaller than a fraction of a proton – some 700 trillion times thinner than a human hair.
It also arrives on the 10th anniversary of the first detection of gravitational waves, in 2015. In the decade since, upgrades have given scientists three times the clarity, with the network now capturing a black hole merger roughly every three days.
“With dozens of signals now being picked up each year, we’re no longer hearing isolated notes,” Sun said. “We’re starting to hear the full symphony of space-time.”