📄 Showing the "Simple" version — "Popular" is not ready yet. Add it to favorites to help prioritize it. Ask for the full read

The James Webb Space Telescope peered into an era when the universe was less than a billion years old and spotted strange objects—'little red dots.' These are black holes with masses of millions of suns, but in very compact, chemically pristine galaxies. Standard scenarios can't grow such heavyweights that early.

A new explanation resembles a shark being fed by a school of small fish. At the center of a dense gas cloud, a seed already sits — a black hole with a mass from a thousand to a hundred thousand suns. Within a few light-years, a swarm of tiny black holes buzzes around: each about thirty times heavier than our Sun. These little ones are primordial black holes, born in the first moments after the Big Bang. Gas slows their motion, and they spiral onto the central giant. Each capture releases about six percent of the victim's mass as gravitational waves, while the rest settles onto the central hole. The whole process takes from ten to fifty million years — by cosmic standards, an instant.

Mergers happen one after another, creating a distinctive gravitational-wave background — a hum that future detectors could hear. Its spectrum has a characteristic slope: loudness increases with frequency following a 'two-thirds' law. At frequencies around 13 millihertz for hundred-thousand-solar-mass holes and around 1 hertz for thousand-solar-mass ones, 'ringdowns' occur — damped oscillations of a newly born hole. Rare collisions of two large seeds would produce single bursts, distinguishable against the general noise.

Such a model doesn't require rare conditions. If primordial black holes exist and are strongly clustered in space, then 'red dots' are a natural outcome of their collective life.