Two Supermassive Black Holes on Verge of Colliding Spotted by Scientists

Astronomers believe they have spotted two colossal black holes orbiting each other that are set to collide in the future—an event so energetic it will shake the fabric of space and time.

The discovery was made by scientists observing a quasar, which is the name given to extremely bright cores of galaxies where gas is superheated to millions of degrees by a supermassive black hole.

The quasar in question, PKS 2131-021, has been studied extensively with radio observations spanning 45 years. Over time, researchers had noticed that the brightness of PKS 2131-021 would sometimes change.

Not only was the light varying periodically, but sinusoidally. In other words, there was a pattern that the researchers could trace.

They think the reason for this is that a jet of light from the quasar is moving back and forth like a ticking clock. They also believe the most likely reason for this is that this quasar is not the result of one huge black hole, but two spinning around each other.

Astronomers knew this was possible, but finding direct evidence of the phenomenon has proven difficult.

The black holes, located around 9 billion light-years from Earth, are thought to be huge. Each has a mass hundreds of millions of times the mass of our sun.

In a study published in The Astrophysical Journal Letters on Wednesday, scientists from several research institutions including CalTech describe how the two black holes of PKS 2131-021 appear to be orbiting each other once every two years, separated by a distance of around 2,000 astronomical units, or 2,000 times the distance from the sun to the Earth.

This may sound large, but in astronomical terms it's practically a hair's breadth. The only other known candidate for supermassive black holes in the process of merging is the quasar OJ 287, in which the two black holes are thought to be 10 to 100 times further apart than the pair in PKS 2131-021, according to a CalTech press release.

NASA's Jet Propulsion Laboratory in California estimates that if one were to take into account the many millions of years these black holes have likely been orbiting each other, they are now more than 99 percent of the way to a collision. In real terms, that means a collision around 10,000 years from now.

It should be noted that the two black holes have not been conclusively identified. As the study says: "While we have not yet proven definitively that PKS 2131–021 is a [supermassive black hole binary], we believe that this is by far the most likely scenario."

Black hole mergers are of interest to astronomers since they are believed to be sources of gravitational waves—ripples in space time caused by highly energetic events that were predicted by Albert Einstein in 1916. Almost 100 years later in 2015, scientists physically sensed these waves using the Laser Interferometer Gravitational-Wave Observatory experiment.

Gravitational waves provide clues to the nature of gravity itself, which is one of the mysteries of the universe.

We don't have to worry about them, though. By the time gravitational waves reach Earth, they are thousands of billions of times smaller than they were at their source. As such, these ripples tend to be 1,000 times smaller than the nucleus of an atom and are incredibly hard to detect.

Black hole
Illustration of a black hole. Colliding black holes are thought to be sources of gravitational waves. solarseven/Getty