Evidence has accrued that they do merge. Last year, observations of the subtle movements of pulsating stars known as a pulsar timing array revealed a background hum of gravitational waves in the universe—ripples in the fabric of space-time. These gravitational waves most likely come from tightly orbiting supermassive black holes within a parsec of each other that are close to merging. "This was our first evidence that black hole binaries do overcome the final-parsec problem," said Laura Blecha, an astrophysicist at the University of Florida.
It was thought in-spiral times could be as high as ... the age of the universe. People were concerned that you might not get any merging black holes. Now, with the evidence of merging found in gravitational waves, the focus shifts to understanding how they close the gap during that crucial final parsec distance between them, a problem previously thought insurmountable.
Astrophysicists have a new suggestion: Dark matter could sap angular momentum from the two black holes and nudge them closer. This could explain how the supermassive black holes can overcome the final parsec problem and eventually merge, revealing insights into the interactions of visible and dark matter in our universe.
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