Super-massive black hole pair on course for cosmic collision
The final act of this mating dance, perhaps a mere million years from now, could release as much energy as 100 million of the violent supernova explosions in which stars end their lives, and wreck the galaxy it is in, said S. George Djorgovski of the California Institute of Technology.
Most of that energy would go into gravitational waves, the violent ripples of space-time that are predicted but not yet directly detected by Einstein's theory of general relativity, Dr. Djorgovski said. And there could be electromagnetic fireworks as well.
© Santiago Lombeyda/Center for Data-Driven Discovery, Caltech
An artist’s conception of two black holes in close orbit. In the distant future, scientists expect two black holes to collide and give off a huge amount of energy.
According to theory, he explained in an email, the interactions of the black holes would drive nearby stars away, like shingles in a tornado. "However," he added, "I think that the nature is never so neat."
Dr. Djorgovski, one of the authors of a paper published in the journal on Wednesday, will discuss the research at a meeting in Seattle. The lead author is Matthew Graham, a computational scientist at Caltech's Center for Data-Driven Discovery.
The merging black holes manifested as a regular flicker in a quasar - a mass of light and energy - in a remote galaxy known as PG 1302-102. The most logical explanation, Dr. Graham and his colleagues wrote, is a pair of black holes circling each other less than a light-year apart.
"This is the most convincing evidence for a tight pair of black holes with a separation smaller than the solar system," said Avi Loeb, a cosmologist at the Harvard-Smithsonian Center for Astrophysics who was not involved in the work, noting that other, less convincing systems have been suspected. He cautioned, moreover, that the evidence is not yet airtight; the apparent variation in the quasar light could be a statistical effect from not checking it frequently enough.
If it holds up under scrutiny, the system could be a bonanza for the young field of gravitational wave astronomy. It would also provide a preview of what will happen in our own Milky Way galaxy in a few billion years when it collides with the neighboring Andromeda galaxy, sending the black holes at the hearts of both galaxies into an "intimate (pre-arranged) companionship," as Dr. Loeb put it in an email.
Black holes are the most extreme consequences of Einstein's theory: maws so deep and dense that not even light can escape. There seems to be one weighing as much as millions or even billions of suns squatting like Dante's Lucifer in the center of every galaxy. Normally they are dormant, but when they feed on stars and gas, burping energy into space, they can light up as quasars, beacons that far outshine the galaxies in which they live.
Mergers of black holes should be common in cosmic history because galaxies are forever merging. Indeed, there are dozens of examples of merging galaxies in which the black holes are separated by tens to thousands of light-years, Dr. Loeb noted, some of them with beautiful jets coming from one or both of the black holes.
Astronomers can rarely see the consummation of these relationships, however, because after billions of years circling each other, the last spasm happens, it is believed, in a million years or so - an unimaginably long time to a human, but unimaginably short to a star or the universe.
Flanked by a pair of smaller galaxies, PG 1302-102 lies about 3.5 billion light-years from here in the constellation Virgo, and has a quasar at its center.
It was spotted in the Catalina Real-Time Transient Survey, which for nine years has been monitoring the brightness of 247,000 known quasars with telescopes in Arizona and Australia.
Dr. Graham found the signal from PG 1302-102 wavered by about 14 percent every 1,884 days, or roughly five years.
The only thing that could so significantly affect a giant black hole, Dr. Djorgovski said, would be another giant black hole. He estimated their combined mass is that of roughly 100 million suns.
The black holes are circling each other at a range of about 180 billion miles, he said. That is far too small to be resolved by any telescopes on Earth, but spectrographic observations suggest there are two things there, the researchers say.
The light variations could be caused by the jets of energy precessing like tops as the black holes sweep around each other, or perhaps warps in the disks of material swirling around them, Dr. Djorgovski said.
The closeness of the black holes would mean that the system has evolved well past the point where supercomputer simulations of the merger would work. To find out what happens, astronomers will have to build gravitational wave detectors and wait and watch.
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