Astronomers study paired black holes in merged galaxies

"The dual black hole we found has the smallest separation of any so far detected through direct imaging," said astrophysicist David Merritt.

By Brooks Hays
Astronomers study paired black holes in merged galaxies
Radio waves coming from NGC 7674, seen just above the center, suggest the luminous spiral galaxy hosts a pair of supermassive black holes inside its active nucleus. Photo by NASA/ESA/Hubble Heritage Team

Sept. 18 (UPI) -- Astronomers have completed a new radio survey of supermassive black holes located in the centers of galaxies. The findings -- published this week in Nature Astronomy -- suggest pairs of supermassive black holes can become gravitationally locked in merged galaxies.

The survey revealed a pair of supermassive black holes inside the luminous spiral galaxy NGC 7674, located 400 million light years from Earth. The two black holes are separated by a single light-year.


"The dual black hole we found has the smallest separation of any so far detected through direct imaging," David Merritt, professor of physics at Rochester Institute of Technology, said in a news release.

The average supermassive black hole has mass a million times greater than the sun. Though the latest survey suggests pairs of supermassive black holes likely collide and merge, researchers have yet to measure the gravitational waves generated by such a collision.

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In 2015, the Laser Interferometer Gravitational-wave Observatory, or LIGO, detected gravitational waves for the first time. But the waves were created by the collision of two stellar-mass black holes, which are thousands of times less massive than supermassive black holes.


"A supermassive binary generates gravitational waves with much lower frequency than the characteristic frequency of stellar-mass binaries and its signal is undetectable by LIGO," Merritt said.

Researchers simulated a more sensitive gravitational wave detector by synching a group of radio telescopes from all over the world.

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"Using very long baseline interferometry techniques, two compact sources of radio emission were detected at the center of NGC 7674; the two radio sources have properties that are known to be associated with massive black holes that are accreting gas, implying the presence of two black holes," Merritt said.

Astronomers measured gravity waves emanating from the zee-shaped galactic system. Scientists have previously predicted such a system would host a large compact binary.

"This morphology is thought to result from the combined effects of the galaxy merger followed by the formation of the massive binary," Merritt said.

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