In what is thought to be the first direct detection of a pair of merging black holes, astronomers have observed a cosmic cataclysm that could test our understanding of how these objects form and evolve.

The finding, published in the journal Nature, offers new clues to the mysterious origins of binary black holes—pairs of black holes that orbit each other before eventually colliding.

"We believe that this event is the result of a pair of black holes that were born when a single massive star exploded," said study lead author Vicky Kalogera, a professor of physics and astronomy at Northwestern University.

The stellar explosion, known as a supernova, would have occurred hundreds of millions of years ago in a galaxy billions of light-years from Earth.

"The two black holes that resulted from the supernova would have been in a very close orbit," Kalogera said. "Over time, they would have radiated away energy and lost angular momentum, causing their orbit to decay and the black holes to spiral inward."

The final plunge would have happened in a fraction of a second, unleashing a burst of gravitational waves—ripples in spacetime that are predicted by Einstein's theory of general relativity.

These gravitational waves would have traveled across the universe and eventually reached LIGO, a pair of giant laser interferometers located in the United States. LIGO is designed to detect these ripples in spacetime.

On May 21, 2019, LIGO detected a gravitational wave signal that matched the predicted signature of a pair of merging black holes.

The event, dubbed GW190521, was the most massive binary black hole merger ever observed by LIGO. The primary black hole had a mass of about 85 times that of the sun, while the secondary black hole had a mass of about 66 times that of the sun.

"The mass of these black holes is particularly intriguing," Kalogera said. "They are both larger than the typical stellar-mass black holes that we have observed so far."

This suggests that GW190521 may have formed through a different mechanism than most other binary black holes.

"It is possible that these two black holes were formed from a massive binary star system," Kalogera said. "In such a system, the two stars exchange mass and eventually merge, forming a single black hole. This black hole could then go on to merge with another black hole to form the binary black hole that we observed."

The discovery of GW190521 is a major milestone in the study of black holes and gravitational waves. It provides new insights into the formation and evolution of these objects and offers a tantalizing glimpse into the violent universe that lies far beyond our reach.