A pair of gargantuan black holes have been found to inhabit the same galaxy and will eventually merge with a violence that will slingshot stars out of the galaxys center and unleash a torrent of radiation and gravitational energy.

The galaxy Komossa and her colleagues examined is about 400 million light-years away, close by astronomical standards in a universe that spans more than 12 billion light years. The two black holes are about 3,000 light-years apart and closing. Each used to anchor a separate galaxy, but the two galaxies begin merging about 30 million years ago, astronomers estimate.

When galaxies merge, individual stars are typically not affected, theorists believe. But with two black holes colliding, thing get a little more chaotic. SPACE.com asked Komossa what will happen.

For now, the two black holes do not feel each others gravity directly, Komossa explained. Stars are unaffected because they are so widely separated. But the overall centers of the two galaxies are interacting gravitationally.

As the black holes draw closer, some stars will begin to feel the effect.

"Individual stars which approach the binary black hole closely are accelerated and finally ejected from the center of the galaxy," she said. "The energy is extracted from the orbital energy of the black hole binary."

The mechanism is the same slingshot effect NASA uses to sent spacecraft around a planet, robbing a tiny bit of the planets energy to give the craft a speed boost and fling it a more distant planet.

When the black holes get as close as 1 light-year apart, they will begin to merge.

"They are now spiraling towards each other," Komossa said of that future event. "The final merging of the black holes, to form a single one of larger mass, will be accompanied by an enormous burst of gravitational waves."

These waves will spread through the universe, causing ripples in the fabric of space that astronomers would be able to detect as tiny changes in distance between two points.

"This is the first time that we see a binary black hole in action, the smoking gun for something which will become a major gravitational wave burst in the future," said Guenther Hasinger, another Max Planck researcher involved in the work.

Meanwhile, theres more to the merger. During the final stages, more and more gas rains down on the two black holes.

Komossa: "The gas will heat itself up in the process, and start to emit huge amounts of radiation, strongly increasing the luminosity of the nucleus of the galaxy, outshining the whole galaxy in its brightness by a large factor. The strong radiation field will start to destroy the dust in the environment of the nucleus, giving an outside observer an even clearer view on the nucleus of the galaxy.

"The powerful radiation will also hinder part of the infalling matter to actually reach the black holes horizon and disappear within the black hole; instead the material will be driven out again by strong radiation pressure, and huge outflows or jets may built up."

When all is said and done, few stars are likely to remain in the vicinity of the merged and more massive black hole.

Komossa said the new findings are indirect evidence that black holes must be in all states of merging around the universe.

She points out that NGC 6240 is relatively nearby, making the new and finely detailed observations possible. Astronomers have seen evidence for active black holes many billions of light years distant.

"The fact that we do see a binary black hole in this galaxy strongly suggests that there are many more out there," she said.

Other studies have shown that several gravitational wave event occur every year. A planned space detector called LISA (Laser Interferometer Space Antenna) would search for them.