2 black holes collided billions of years ago. The spectacle is just beginning to reach Earth.

In a galaxy far, far away, two giant black holes appear to be circling each other like fighters in a galactic boxing ring.

Gravity is causing this death spiral, which will result in a collision and formation of a single black hole, a massive event that will send ripples through space and time. 

The collision itself happened eons ago — the two black holes are located about 9 billion light years from Earth. Scientists won’t be able to document it for 10,000 years. Even so, there are imperceptible gravitational waves generated before the collision that are hitting us right now.

These waves from the black holes’ activity will increase, but will not affect Earth. However, they could help increase our understanding of how our universe has evolved.

Such supermassive black holes “are the most powerful and energetic objects in the universe and they have an enormous effect on the evolution of galaxies and stars,” Tony Readhead, an astronomy professor at the California Institute of Technology, told USA TODAY. He is the co-author of the report by Caltech astronomers who detail the discovery in The Astrophysical Journal Letters, a peer-reviewed scientific journal.

“If we want to understand the evolution of our universe we need to understand these objects,” Readhead said.

Black holes: Two will merge into one

Black holes are invisible spots in the galaxy where gravity pulls in all matter and light, according to NASA. Even though black holes are invisible, scientists can find them because they can study how stars near them behave differently.

Each of the black holes identified in this study has a mass amounting to hundreds of millions of times more than that of our sun, the researchers say. It took about 100 million years for the two objects to converge on their orbit, which has them at a distance of about 50 times that separating our sun and Pluto, NASA said. The two black holes are more than 99% of the way toward colliding, the agency said.

Most large galaxies contain a supermassive black hole at its center, scientists have found. “Astronomers don’t know how these objects get to be quite so big, but one possibility is that the universe’s largest black holes result from at least one merger between two smaller black holes,” according to NASA,” wrote Brandon Specktor on the Live Science news site. “The new study may help to confirm that hypothesis.”

The Caltech research team came across this rare case of a binary, the term for two big black holes orbiting one another, while studying quasars.

Quasars arise at the center of a galaxy where gravity is pulling matter into a black hole, but some particles escape and are jettisoned away at almost the speed of light. That jet of particles is called a quasar; quasars with particle jets aimed directly at the Earth are extremely bright and are called blazars.

While studying about 1,800 blazars using the Owens Valley Radio Observatory in Northern California, the scientists noticed this particular blazar – named PKS 2131-021 – had a regular pattern of radio wavelengths, electromagnetic waves we cannot see but can be measured by radio telescopes.

That led them to look at the quasar’s activity captured over decades from other radio telescopes across the world and NASA’s Wide-field Infrared Survey Explorer (WISE) space satellite. 

“When we realized that the peaks and troughs of the light curve detected from recent times matched the peaks and troughs observed between 1975 and 1983, we knew something very special was going on,” said Sandra O’Neill, lead author of the new study and a Caltech undergraduate student, in a description of the research on the university’s website.

The regular radio wavelength fluctuations, akin to the ticking of a clock “strongly suggests that this blazar harbors not one supermassive black hole, but two supermassive black holes orbiting each other,” Readhead said in the research description.

This is only the second pair of orbiting black holes identified by scientists, the researchers say. Space-time undulations from gravitational waves made by two colliding black holes 1.3 billion light-years away were recorded in 2015 by the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory.

As these two most recently discovered black holes get closer to each other, they will send off ever larger gravitational waves. The Caltech team is currently trying to detect these ripples in the space-time continuum.

Because of the speed of light, what the scientists are recording has already happened. “So the actual collision took place just under 9 billion years ago, but we won’t be able to see it on earth for 10,000 years,” Readhead said.

In the meantime, those ripples will disrupt space and time – as Einstein predicted more than 100 years ago with in his theory of relativity – but by the time they hit our galaxy and Earth, they pose no danger, nor does the collision of the black holes.

“These two supermassive black holes are so far away that we will not have to worry about any effects from their merger, and, in general, the size of the gravitational waves is still so small that we don’t have to worry,” Joseph Lazio, a co-author on the paper and chief scientist of the Interplanetary Network Directorate at the Jet Propulsion Laboratory at the California Institute of Technology, told USA TODAY via email.

“The gravitational waves are essentially ‘ripples’ in space and time,” he said. “In fact, there should be some washing over the Earth as I write this email and also while you read it.”

This article originally appeared on USA TODAY: 2 black holes collided billions of years ago. The spectacle is just beginning to reach Earth.

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