Pair of Black Holes Found Waltzing
In a looming collision of giants, two super-massive 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 orbiting 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 super-massive 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 in the constellation Ophiuchus known as NGC 6240. Because of its distance from the Earth, the image now seen is 400 million years old.
Although NGC 6240 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 that as the galaxies of NGC 6240 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 mph, Hasinger said.
When the black holes 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 astrophysicist 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 ripple across space will be such that a planet could pulsate,” said Sigurdsson. “A whole planet could be squeezed by an inch or so every few minutes,” depending on how close it is to the merged black holes. Satellites would jiggle and navigation equipment could wobble momentarily, he said.
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.
Hasinger said the two black holes have enormous appetites -- each minute sucking in mass about equal to that of the sun.
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, each with a mass of 3 1/2 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 NGC 6240, are much larger, equal perhaps to many millions of solar masses, and are usually at the center of a galaxy. The Milky Way, home galaxy of our solar system, has a black hole at its center.
With its immense gravitational pull, a black hole can suck in gas, dust and other matter from surrounding space. Entire stars can be stripped and pulled into the bottomless maw.
As it spirals in at near light speeds, matter captured by a black hole heats by millions of degrees and gives out intense radiation in several parts of the spectrum, including X-rays. The Chandra observatory can detect these X-rays down to the very edge of the black hole and relay the data to Earth for study by astronomers.
