Astronomers announced on Thursday that they had discovered a giant black hole surrounded by a litter of young protogalaxies that date to the early universe — the beginning of time.

The black hole, which powers a quasar known as SDSS J1030+0524, weighed in at a billion solar masses when the universe was only 900 million years old. It and its brood, the astronomers said, represented the infant core of what became a vast cluster of galaxies millions of light years across and encompassing a trillion suns worth of matter.

The discovery should help astronomers understand the origins of galactic clusters— the largest structures in the universe — and how supermassive black holes could have grown so quickly in the early universe. And it provides a rare glimpse of the cosmic web, a network of filaments spanning the cosmos that determine the large-scale distribution of matter in the universe.