Astronomers announced 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 that determine the large-scale distribution of matter in the universe.

“These are extreme systems, and to date we have had no good explanation for their existence,” said Marco Mignoli, an astronomer at the National Institute for Astrophysics who was the lead author of a paper published in Astronomy & Astrophysics.

Astronomers have long thought that black holes and massive galaxies should appear earliest and grow fastest at the dense nodes where these filaments cross, where there is abundant gas to feed them. The new results suggest this is true, said team member Colin Norman of Johns Hopkins University.

“This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the universe,” the astronomers wrote in their paper. The finding, they added, lent support to the idea that the most distant and massive black holes formed and grew within massive halos of dark matter in large-scale structures.”

One of the primary goals for the next generation of “super telescopes,” like the Giant Magellan Telescope and the European Extremely Large Telescope, both now being built in Chile, is to map out this web with greater fidelity. “The added light-gathering power of the next generation will allow us to use faint young galaxies to serve as the back lights” illuminating the faint filaments of atomic matter, said Alan Dressler of the Carnegie Observatories.