Giant Black Holes — Children of Mergers ✛ ✎ ✦
Gravitational waves (ripples in spacetime) are recorded by LIGO detectors (concept by Einstein and Schwarzschild with Weiss). Analysis of 259 black hole mergers revealed that slow-spinning holes (born from single stars) and fast-spinning ones are not different kinds, but parents and children. The masses of fast ones precisely match the sum of two slow ones — as if offspring inherit their ancestors' weight.
The long search for black holes in the mass gap between light ones (remnants of supernovae) and heavy ones is finally over. This gap turned out to be a cradle: descendant holes emerge after several mergers. Each merger births a new hole that spins faster than its parents. Growth from pulling in gas (accretion disk) couldn't explain such a tidy picture.
Analyzing the mass cutoff for slow holes helped clarify how heavy elements are born inside stars and how stellar evolution depended on cosmic epoch (redshift). The family history of black holes holds the key to the chemistry of the Universe.
The mass gap is filled not by direct birth, but by a chain of mergers: here each hole is an heir to the previous ones, like a link in a cosmic dynasty.
In Liu Cixin's "The Three-Body Problem," universes are born from universes. Similarly, black holes spawn new generations by merging with one another.