The Theory of How Black Holes Grow
Astrophysicists in the U.S. have developed a theoretical model for black holes to predict if growth by gas accretion or by merger is dominant. It’s valid, they say, from the local Universe up to redshift 10 (roughly from the present day to about 13 billion years ago) — and it suggests that the main growth channel depends on the mass of the black hole and on redshift. In the nearby Universe, small black holes grow mostly by accretion, while very big black holes grow mostly via mergers. In the very-far-away Universe, there is a reversal: small black holes grow mostly by mergers, big black holes by accretion.