Early star collisions may seed supermassive black holes

How could a supermassive black hole form before age 1 billion?

JWST began spotting these objects in 2022. Their existence before the universe reached 1 billion years old has puzzled astronomers because black holes should need at least 1 billion years of feeding and merging to reach “supermassive” status.

Feeding means drawing in gas and other material; merging means joining another black hole. Supermassive black holes have millions or billions of times the Sun’s mass.

One proposed solution is that supermassive black holes did not start from zero. They grew from intermediate-mass black holes, which act as seeds. Astronomers divide black holes into three broad classes:

• Stellar-mass black holes: 10 to 100 times the Sun’s mass, produced when a massive star collapses.
• Intermediate-mass black holes: 100 to 100,000 times the Sun’s mass, thought to lie between stellar remnants and supermassive black holes.
• Supermassive black holes: Millions to billions of times the Sun’s mass, at the centers of modern galaxies.

No single star should have enough mass to collapse into an intermediate-mass black hole under the conditions of our present, 13.8-billion-year-old cosmic neighborhood. The simulations instead place the necessary mass in crowded early-universe clusters. That setting gives a black-hole seed a head start.

Williams also said the cluster environment can provide stars and gas that influence the black hole’s later growth, not just its formation.

In plain terms: an early seed gives a supermassive black hole a head start that it would not otherwise have.

What are the Little Red Dots?

JWST routinely finds extremely compact objects in the early universe that look like red dots, hence their name. They seem to have disappeared by the time the cosmos reached 2 billion years old.

Several ideas compete to explain them. One says each object hosts a rapidly growing black hole. The simulations add a specific possibility: a Little Red Dot may be a dense star cluster shaken by repeated collisions. Those collisions build a very large star, which eventually collapses into an intermediate-mass black hole.

Smadar Naoz, a UCLA researcher and team member, said:

“Little Red Dots are a hot topic in astronomy.”

Naoz compared competing studies to blind people trying to describe an elephant by touching different parts of it. She said the new research connects several partial views and may reveal more of the whole object.

In plain terms: the same crowded clusters could account for both the red compact objects and the heavy black holes they may contain.

Why would Little Red Dots vanish by age 2 billion?

Less than 1 billion years after the Big Bang, the universe lacked well-ordered spiral galaxies. Dense, chaotic regions of star birth filled it instead. Repeated collisions in those regions could build ultra-massive stars and then intermediate-mass black holes.

As the universe cooled and expanded, those sites became building blocks for much less chaotic galaxies. If Little Red Dots require an extreme, collision-rich cluster to exist, a move toward a calmer state would remove the conditions that sustain them. The cosmos would no longer be extreme enough to keep them.

In plain terms: as cosmic density fell, the conditions that made Little Red Dots disappeared with it.

What does the model change for astronomers?

The model links both puzzles to dense, collision-rich clusters, but the evidence remains simulation-based. It does not confirm that any observed Little Red Dot is such a cluster, and other explanations remain in play. The result also assumes slow mergers, collapse into a heavy remnant and a cluster-to-galaxy transition.

For astronomers, the practical payoff is one shared physical explanation for unusually massive black holes and compact red sources.

In plain terms: crowded young clusters may be the missing link between two early-universe puzzles, but the simulations do not make that link certain.