Research

Supermassive black hole pairs imaged in merging galactic cores

Supermassive black hole pairs imaged in merging galactic cores

Some of the most powerful objects in the entire universe are black holes. Most prior observations of colliding galaxies have caught the coalescing black holes at earlier stages when they were about 10 times farther away.

The final stage of a merger between pairs of black holes in the cores of colliding galaxies.

"Seeing the pairs of merging galaxy nuclei associated with these huge black holes so close together was pretty unbelievable", Michael Koss, one of the researchers who studied the images, said in a release.

At the center of the merging galaxies is a pair of black holes that once lived at the center of each of the two smaller galaxies; these black holes are drawing closer and closer to each other and will eventually merge into one more massive black hole.

Then they looked for galaxies that matched these X-rays using data from NASA's Hubble Space Telescope and the Keck Observatory in Hawaii.

The images were taken by the Hubble Telescope's Wide Field Camera 3, and they show the galaxy NGC 6240.

The high-resolution images have provided the scientists with a close-up of galactic collisions, something which is believed to have been more frequent in the early universe. The black holes located in the very heart of the colliding galaxy are rapidly expanding since they consume the energy that is being produced by two cores.

In about 6 billion years, scientists estimate that the Milky Way will merge with the Andromeda galaxy into one big galaxy. Structure is giving way to chaos, but hiding behind this messy cloud of material are two supermassive black holes, nestled at the center of each of the galaxies, that are now excitingly close, giving astronomers the best view yet of the pair marching toward coalescence into one mega black hole.

The scientists first searched for hidden black holes by sifting through 10 years' worth of X-ray data from NASA's Neil Gehrels Swift Observatory.

To check their results, they compared the survey galaxies with a control group of 176 other galaxies, from the Hubble archive, that lack actively growing black holes.

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The resulting pictures were "part of the largest-ever survey of the cores of nearby galaxies using high-resolution images in near-infrared light taken by the Hubble and Keck observatories", according to the news release. The two merging galaxies the team is studying are an average of 330 million light-years from Earth; these galaxies are similar in size to the Milky Way and Andromeda.

The researchers found that more than 17% of galaxies had a pair of black holes at their center. This speedy growth occurs during the last 10 million to 20 million years of the union.

It's not easy finding galaxy nuclei so close together either.

NASA says that a galaxy merger is a slow process that can take even more than a billion years. The sample galaxies are representative of what astronomers would find by conducting an all-sky survey.

"Computer simulations of galaxy smashups show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that's what we have found in our survey", said Laura Blecha, assistant professor of physics at the University of Florida and a co-author of the study.

The new work was detailed online today (Nov. 7) in the journal Nature.

The team's results support the theory that galaxy mergers explain how some supermassive black holes become so monstrously large.

Gravitational waves are considered ripples in this fabric.

Researchers were able to obtain the images by observing the thick layers of gas and dust that can be found around the cores of the clashing galaxies. Gravitational wave detectors tell astronomers what area, and Koss' research tells them whether that object is likely to host a supermassive black hole merger.

"Our data argues for the second case, that these galaxy mergers are really critical in fueling the growth of supermassive black holes".