The regions of spacetime are famous because their gravity is so strong that nothing – not even light – can escape. They are formed when massive stars collapse and can continue to grow by absorbing and merging with other black holes. This interaction has been observed for decades and scientists use it to identify their presence, as radiation is given off as visible light across space. 

In 1971, Prof Hawking penned “Hawking’s area theorem”, a law that predicts this area, known as the event horizons.

Half a century later, physicists at MIT and have now confirmed it for the first time, using observations of gravitational waves. 

Their findings appeared in “Physical Review Letters” this month and show the result of a study into GW150914, the first gravitational wave signal detected by the Laser Interferometer Gravitational-wave Observatory (LIGO), in 2015.

The signal was created as a result of two merging black holes that are said to have given birth to another.

The experts found that, with 95 percent confidence, the total event horizon area did not decrease after the merger – confirming Hawking’s prediction that the new black hole should not be smaller than the total horizon area of its parents.

Their findings mark the first direct observational confirmation of Hawking’s area theorem, which has been proven mathematically but never observed in nature until now.

The team plans to test future gravitational wave signals to see if they might further confirm Hawking’s theorem or be a sign of new, law-bending physics.

NASA Einstein Postdoctoral Fellow and lead author Professor Maximiliano Isi, said: “It is possible that there’s a zoo of different compact objects, and while some of them are the black holes that follow Einstein and Hawking’s laws, others may be slightly different beasts.

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“So, it’s not like you do this test once and it’s over. You do this once, and it’s the beginning.”

Their big breakthrough came in 2019 when the team developed a technique to extract the reverberations immediately following GW150914’s peak — the moment when the two-parent black holes collided.

Prof Isi added: “The data shows with overwhelming confidence that the horizon area increased after the merger, and that the area law is satisfied with very high probability.

“It was a relief that our result does agree with the paradigm that we expect, and does confirm our understanding of these complicated black hole mergers.

“It’s encouraging that we can think in new, creative ways about gravitational-wave data, and reach questions we thought we couldn’t before,

“We can keep teasing out pieces of information that speak directly to the pillars of what we think we understand. One day, this data may reveal something we didn’t expect.”

Their research was supported, in part, by NASA, the Simons Foundation, and the National Science Foundation.