Three Super-Massive Black Holes Merging Together in Our Nearby Universe

Re:Three Super-Massive Black Holes Merging Together in Our N... by chasil on Sunday August 29, 2021 @10:29AM (#28346980)

The article mentions the "final parsec problem," which implies that a binary pair will never merge. A three-body arrangement is one scenario where a merger can take place.

"Gravitational waves can cause significant loss of orbital energy, but not until the separation shrinks to a much smaller value, roughly 0.01–0.001 parsec."

https://en.wikipedia.org/wiki/Binary_black_hole#Final_parsec...

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Re:Three Super-Massive Black Holes Merging Together in Our N... by ncmncm on Sunday August 29, 2021 @09:03PM (#28351914)

Thank you. This seems to suggest that the black-hole mergers picked up by LIGO must have involved an unseen third participant. Or is this required only for supermassive black holes to merge?

Is there any rational hope of picking up (e.g.) periodically varying red-shift of secondary radiation from the (presumably large) collection of black-hole pairs stuck in parsec-range orbits? Is there any process tending to align the rotational axes of accretion discs on bodies in this condition?

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