Northwestern University researchers have made a notable discovery regarding binary black holes in star clusters. Contrary to previous beliefs that these black holes have randomly distributed spins, new simulations suggest that their spins align with the binary orbit before merging.
Fulya Kıroğlu, a graduate student at Northwestern's Weinberg College of Arts and Sciences, led the study. She explains that as binary black holes collide with massive stars and consume the resulting stellar debris, their increased mass enhances gravitational pull. This realigns their spins to match their orbital motion. Kıroğlu stated, "When a massive star is torn apart by a binary black hole, it creates two separate streams of debris, each spiraling around one of the black holes."
The study highlights how tidal forces gradually influence spin direction during this process. Over time, this results in slight but consistent alignment seen in gravitational wave signals from merging binary black holes detected by LIGO/Virgo. The findings challenge the long-held belief about random spin distribution among such celestial bodies.
This research has been accepted for publication by The Astrophysical Journal Letters and involves collaboration with Allegheny College and the University of California, San Diego.
Kıroğlu works under Professor Fred Rasio at Northwestern's Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Their work offers new insights into cosmic phenomena and contributes to understanding gravitational wave signals better.