Rachel S. Somerville

A field sown with seeds. Some seeds are large and sprout at the slightest rain; others are finicky, requiring special soil and rare conditions. Which seeds fall into the ground determines what kind of forest will grow years later. Astrophysicists think about the birth of black holes in the early universe in much the same way.

A marathon lasting 13 billion years started with different weights. A hundred solar masses — lighter than some gas clouds. A hundred thousand — gravitational dominance, comparable to an elephant among kittens. That's what black hole seeds looked like, ones that by our time should have turned into supermassive giants.