Albert Einstein and Stephen Hawking were right.
A newly discovered collision between two black holes has offered the strongest evidence yet of the two legendary physicists' long-held theories about these mysterious cosmic objects, areas in space of such intense gravity that nothing—not even light—can escape from them.
Astronomers using the powerful Laser Interferometer Gravitational-Wave Observatory, or LIGO, detected the astronomical smash-up at the beginning of this year, their discovery revealing gravitational waves—faint ripples in space-time produced by the two black holes slamming into each other—in the most extraordinary detail to date.
The researchers announced their findings last month in the journal Physical Review Letters.
"Unlike other electromagnetic studies where we see the effects of black holes on the surrounding matter, here we can study for the first time the properties of black holes themselves and obtain much better evidence of the general relativistic effect," Nico Cappelluti, an associate professor of astrophysics at the University of Miami College of Arts and Sciences who studies supermassive black holes, said of the discovery.
Video: NASA's Goddard Space Flight Center
Improvements to LIGO's key components, including its lasers and mirrors, helped make the recent discovery three times more precise than the instrument's initial detection of gravitational waves in 2015, when it picked up a signal from the collision of two black holes that had occurred more than a billion years ago.
The latest discovery—dubbed GW250114 because astronomers detected the gravitational wave signal on January 14, 2025—has allowed researchers to validate predictions made several decades ago by the genius physicists Einstein and Hawking.
Conceived by the New Zealand mathematician Roy Kerr in 1963, the first prediction expands on Einstein's theory of general relativity, stating that black holes are fundamentally simple objects that can be described by just two numbers: their mass and their spin.
The second, advanced by Hawking in 1971, asserts that when two black holes merge, the resulting surface area, known as a black hole's event horizon, must be equal to or greater than the combined areas of the original two black holes.
"If Einstein and Hawking were alive today, I'm sure this new discovery would have impressed them to no end," Cappelluti said. "What LIGO detected has allowed their legacies to live on forever."
For Cappelluti, the LIGO detection and future observatories that will follow it have important implications for his own research on supermassive black holes, which have hundreds of thousands to billions of times the mass of the Sun and can be found at the centers of most large galaxies, including our own Milky Way.
"How supermassive black holes form and grow is one of the great mysteries of the universe," he said. "There are two main channels for their growth: one is the merger of black holes, such as what astronomers observed with LIGO. And the other is the process of accretion, where black holes get bigger by swallowing matter around them. Studying these two growth channels is important because we can, in that way, model how black holes grow and how this growth is related to the evolution of the galaxy within which they live."
LIGO, a set of two identical observatories located in Livingston, Louisiana, and Hanford, Washington, cannot detect the merger of supermassive black holes, Cappelluti said. "It can't see the much-longer wavelengths that would be created by such an event," he said. "For that, we'll have to wait for LISA."
Cappelluti is referring to the European Space Agency's Laser Interferometer Space Antenna, a NASA-supported space-based observatory expected to launch in the mid-2030s that will detect gravitational waves beyond the capabilities of ground-based observatories.
"We're launching telescopes and sending rovers to distant planets to help answer questions about our universe. And each time we find answers, we generate a myriad of new questions," said the researcher. "It's a dynamic time to be in the field of astronomy."
