Washington ? In a looming collision of giants, two supermassive black holes are drifting toward a violent merger and an eruption of energy that will warp the fabric of space. It is all happening in a bright galaxy 400 million light years away.

Images from the Chandra X-ray Observatory have captured for the first time the circling dance of two black holes – each millions of times the mass of the sun – as they whirl around each other in a 100-million-year pirouette to merger.

“This is the first time we have ever identified a binary black hole,” said Stefanie Komossa, an astronomer at the Max Planck Institute for Extraterrestrial Physics and the co-author of a study of the double black hole.

“This is the aftermath of two galaxies that collided sometime in the past.”

Each of the galaxies was about the size of the Milky Way, with billions of stars, and each contained at its center a supermassive black hole with a mass equal to perhaps 100 million suns, Komossa said Tuesday at a news conference announcing the discovery. When they blended, the galaxies formed a single, extraordinarily bright galaxy known as NGC6240. Because of its distance from the Earth, the image now seen is 400 million years old.

Although NGC6240 is far away, astronomers said the merger is a glimpse of what may await the Earth’s galaxy. Astronomers believe that in about 4 billion years, the billions of stars and the black holes of the Milky Way and of the nearby Andromeda galaxy will collide and merge.

“We’re seeing our own future,” said Steinn Sigurdsson, a Pennsylvania State University astronomer who participated in the news conference as a visiting expert.

The astronomers said as the galaxies of NGC6240 merged, the two black holes began circling each other, starting a 100-million-year spiral toward a collision that was expected to spew radiation and gravitational waves across the universe. That collision would not be viewed on Earth for at least another 100 million years, the astronomers said.

Gunther Hasinger, a Max Planck astrophysicist and co-author of the study, said the Chandra images indicate the black holes are about 3,000 light years apart and circling each other at a speed of about 22,000 mph.

As they grow closer and closer over millions of years, the circling speed will get faster and faster, eventually approaching the speed of light, about 671 million miles an hour, said Hasinger.

When the black holes do merge, much of the angular momentum of their waltz will be converted into gravitational waves that will race across the universe, touching and affecting everything they pass, Hasinger said.

Joan Centrella, a NASA astrophysicists who did not participate in the Chandra study, said the merger would briefly warp the fabric of space, just as a pebble thrown into a still pond will cause bank-to-bank ripples. The effect of the gravitational waves on other stars, galaxies and planets will be like the way ripples in that pond cause floating leaves to rise and fall slightly, said Centrella.

The merge will also trigger an enormous eruption of light and X-rays, spewing in all directions, along with jets of plasma matter racing out of the ends of the doughnut-shaped cloud of dust and gas swirling about the black holes.

A black hole is a point in space so dense with matter that its gravitational field will not let anything – not even light – escape.

Stellar black holes, equal to a mass 3.5 to 15 times that of the sun, can be formed by the collapse of a single massive star. But galactic black holes, such as those in NGC6240, are much larger, equal perhaps to many millions of solar masses, and are usually at the center of galaxies. The Milky Way, home galaxy of the sun and its planets, has a black hole at its center.