Do black hole mergers happen on different timescales depending on their mass?

Using the latest gravitational-wave catalog (GWTC-4), researchers found that black hole binaries don't merge on a single universal timeline — their delay between star formation and merger depends strongly on their mass, mass ratio, and spin. Systems heavier than 45 solar masses behave differently from lighter ones, and equal-mass, low-spin pairs wait longer to merge. The merger rate at today's cosmic epoch varies by a factor of 20 across the three identified groups, ruling out a one-size-fits-all description of how black hole pairs form and collide.