Astronomers discover close-knit pairs of massive black holes

Jan 12, 2011
Three of the newly discovered black-hole pairs. On the left are images from the Sloan Digital Sky Survey. The images on the right show the same galaxies taken with the Keck telescope and the aid of adaptive optics, revealing pairs of active galactic nuclei, which are powered by massive black holes. Credit: S. George Djorgovski

Astronomers at the California Institute of Technology (Caltech), University of Illinois at Urbana-Champaign (UIUC), and University of Hawaii (UH) have discovered 16 close-knit pairs of supermassive black holes in merging galaxies.

The discovery, based on observations done at the W. M. Keck Observatory on Hawaii's Mauna Kea, is being presented in Seattle on January 12 at the meeting of the American Astronomical Society, and has been submitted for publication in the .

These black-hole pairs, also called binaries, are about a hundred to a thousand times closer together than most that have been observed before, providing astronomers a glimpse into how these behemoths and their host galaxies merge—a crucial part of understanding the evolution of the universe. Although few similarly close pairs have been seen previously, this is the largest population of such objects observed as the result of a systematic search.

"This is a very nice confirmation of theoretical predictions," says S. George Djorgovski, professor of astronomy, who will present the results at the conference. "These close pairs are a missing link between the wide binary systems seen previously and the merging black-hole pairs at even smaller separations that we believe must be there."

As the universe has evolved, galaxies have collided and merged to form larger ones. Nearly every one—or perhaps all—of these large galaxies contains a giant black hole at its center, with a mass millions—or even billions—of times higher than the sun's. Material such as interstellar gas falls into the black hole, producing enough energy to outshine galaxies composed of a hundred billion stars. The hot gas and black hole form an active galactic nucleus, the brightest and most distant of which are called quasars. The prodigious energy output of active galactic nuclei can affect the evolution of galaxies themselves.

While galaxies merge, so should their central , producing an even more massive black hole in the nucleus of the resulting galaxy. Such collisions are expected to generate bursts of gravitational waves, which have yet to be detected. Some merging galaxies should contain pairs of active nuclei, indicating the presence of supermassive black holes on their way to coalescing. Until now, astronomers have generally observed only widely separated pairs—binary quasars—which are typically hundreds of thousands of light-years apart.

"If our understanding of structure formation in the universe is correct, closer pairs of active nuclei must exist," adds Adam Myers, a research scientist at UIUC and one of the coauthors. "However, they would be hard to discern in typical images blurred by Earth's atmosphere."

The solution was to use Laser Guide Star Adaptive Optics, a technique that enables astronomers to remove the atmospheric blur and capture images as sharp as those taken from space. One such system is deployed on the W. M. Keck Observatory's 10-meter telescopes on Mauna Kea.

The astronomers selected their targets using spectra of known galaxies from the Sloan Digital Sky Survey (SDSS). In the SDSS images, the galaxies are unresolved, appearing as single objects instead of binaries. To find potential pairs, the astronomers identified targets with double sets of emission lines—a key feature that suggests the existence of two active nuclei.

By using adaptive optics on Keck, the astronomers were able to resolve close pairs of galactic nuclei, discovering 16 such binaries out of 50 targets. "The pairs we see are separated only by a few thousands of light-years—and there are probably many more to be found," says Hai Fu, a Caltech postdoctoral scholar and the lead author of the paper.

"Our results add to the growing understanding of how and their central black holes evolve," adds Lin Yan, a staff scientist at Caltech and one of the coauthors of the study.

"These results illustrate the discovery power of adaptive optics on large telescopes," Djorgovski says. "With the upcoming Thirty Meter Telescope, we'll be able to push our observational capabilities to see pairs with separations that are three times closer."

Explore further: Mysterious dance of dwarfs may force a cosmic rethink

More information: Images of some of the merging systems are available at

Related Stories

Merging galaxies create a binary quasar (w/ Video)

Feb 03, 2010

Astronomers have found the first clear evidence of a binary quasar within a pair of actively merging galaxies. Quasars are the extremely bright centers of galaxies surrounding super-massive black holes, and ...

Scientists Find Closest Pair of Supermassive Black Holes

May 01, 2006

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope have found the closest pair of supermassive black holes ever discovered in the Universe -- a duo of monsters ...

Black Holes Go 'Mano a Mano'

Oct 06, 2009

( -- Two black holes in galaxy NGC 6240 are only 3,000 light years apart -- and getting closer.

Active galaxies are different near and far

Jan 06, 2009

( -- An ongoing X-ray survey undertaken by NASA's Swift spacecraft is revealing differences between nearby active galaxies and those located about halfway across the universe. Understanding these ...

Recommended for you

Transiting exoplanet with longest known year

20 hours ago

Astronomers have discovered a transiting exoplanet with the longest known year. Kepler-421b circles its star once every 704 days. In comparison, Mars orbits our Sun once every 780 days. Most of the 1,800-plus ...

Mysterious dance of dwarfs may force a cosmic rethink

Jul 21, 2014

( —The discovery that many small galaxies throughout the universe do not 'swarm' around larger ones like bees do but 'dance' in orderly disc-shaped orbits is a challenge to our understanding of ...

Is our solar system weird?

Jul 18, 2014

Is our Solar System normal? Or is it weird? How does the Solar System fit within the strange star systems we've discovered in the Milky Way so far?

User comments : 7

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jan 12, 2011
I am assuming that the spectra were screened to insure that the pairs were not the result of gravitational lensing effects.
1 / 5 (4) Jan 12, 2011
I have shared on "Astro=boys" pages before that these pairs of black holes are circuit connectors and that one went one way and of course the other fed opposite in the pair.
You would find that these connectors are at each galaxies "Side boundary" if you could just overlay the glue "map" and I even gave out the clues for that also.
Oh,and such a bad,bad wording that you folks have "Glommed onto" Gravitational lensing.Bad,bad boys.
The universe is engineered,not bang created,your Phd claiming so owes you boys alot of money.
The reset will finally silence the place.
5 / 5 (2) Jan 12, 2011
@ Dr Tom:
How did you escape The Matrix?
not rated yet Jan 12, 2011
No, I don't think he did.
1 / 5 (4) Jan 13, 2011
Someones screwed me around,and my security agreement is null and void,so if you call that escaping the matrix.
Anti grav is easy and it takes just 4 to 8 days to get to mars. Take that NSA As------, you boys owe me my money and our science case.
not rated yet Jan 13, 2011
Someones screwed me around,and my security agreement is null and void,so if you call that escaping the matrix.
Anti grav is easy and it takes just 4 to 8 days to get to mars. Take that NSA As------, you boys owe me my money and our science case.

Excellent. An interesting article AND a floor show :-)
1 / 5 (1) Jan 13, 2011
Starship show soon.And you're so used to Budweiser.