Astronomers have identified two supermassive black holes, collectively known as PKS 2131-021, that are on the brink of a catastrophic collision. Located about 9 billion light-years from Earth, these black holes have been spiraling toward each other for 100 million years and now orbit one another every two years. The discovery, published in The Astrophysical Journal Letters, reveals a fascinating binary system that could help scientists understand how black holes form and merge.

PKS 2131-021 is a type of black hole known as a blazar, characterized by jets of supercharged plasma directed at Earth. These jets, which originate from the hot gas swirling around the black hole, travel at nearly the speed of light. When researchers observed the brightness of about 1,800 blazars across the universe, PKS 2131-021 stood out due to its regular fluctuations, akin to the ticking of a clock. This periodic dimming and brightening is believed to result from the gravitational influence of a second black hole in orbit.

To confirm this, scientists analyzed 45 years of data from five observatories. The findings matched predictions, confirming that the brightness variations were caused by a binary black hole system.

These black holes are inching closer together and are expected to collide in roughly 10,000 years, unleashing massive gravitational waves that will ripple across the universe. Gravitational waves, first predicted by Albert Einstein, are distortions in space-time caused by massive objects moving at extreme speeds. Observing PKS 2131-021 now could provide critical insights into these phenomena before the collision occurs.

PKS 2131-021 is the second confirmed binary black hole system, and its members are much closer than those of the first system discovered in 2020. That system’s black holes, located 3.5 billion light-years away, orbit each other every nine years, compared to PKS 2131-021’s two-year orbit. This makes PKS 2131-021 the tightest binary pair yet detected.

The findings also support the theory that supermassive black holes grow larger through mergers of smaller black holes. As these titanic objects collide, they provide an unprecedented opportunity to study the universe’s most extreme events. Future observations of PKS 2131-021 will aim to detect gravitational waves and further explore this extraordinary system.