At the center of a tiny galaxy lies a dense clump of stars and dark matter. This clump, called a soliton, is not frozen in place: it quivers and oscillates like jelly on a plate. These oscillations create ripples in the surrounding dark matter cloud, and this ripple, like gentle nudges, has been pushing stars farther from the center for billions of years. Thus, the stellar population of the galaxy slowly spreads out, turning a compact sphere into a diffuse cloud.
Astrophysicists built a computer model where dark matter behaves not as a collection of particles but as a single wave, so-called wave dark matter. In this model, stars undergo random walks, and their final distribution follows a simple law: density falls smoothly from the center to the edge, in a bell-shaped curve. Remarkably, this is exactly what astronomers see in real dwarf galaxies — satellites of our Milky Way. The more massive the galaxy, the stronger its central clump quivers, and the faster the stars spread out.
Thus emerges a unified scenario: from the faintest dwarfs to giant diffuse galaxies, all are just pages of one story, where time and the trembling of dark matter paint the observed diversity. No 'failed' galaxies, no special formation paths — only age and continuous stirring.
The oldest dwarf galaxies have 'spread out' so much that their stars are now hundreds of times farther from the center than they were when the galaxy was born.
In Greg Egan's novel 'Dark Beyond the Edge', dark matter turns out to be a quantum field whose fluctuations can influence the motion of stars, just like in this model.