---
title: "Dark matter in small galaxies"
description: "Cold, warm, fuzzy and self-interacting dark matter, and gas feedback: what each does to a dwarf galaxy’s centre and to the number of small halos."
canonical_url: "https://sandboxphysics.com/stories/dark-matter-small-scales/"
language: "en"
page_type: "story"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/stories/dark-matter-small-scales/"
last_modified: "2026-11-14"
---

# Dark matter in small galaxies

Sandbox Physics · 2026-11-12

Start with a dwarf galaxy’s rotation speed. Build the cold cusp, remove small-scale power with warm and fuzzy dark matter, make cores with waves, collisions and gas, then recompute the benchmarks and read a published satellite census.

1. L1 · Concept

   ## [Can different dark matter leave similar small galaxies?](https://sandboxphysics.com/stories/dark-matter-small-scales/similar-dwarfs-different-dark-matter/)

   Yes. Waves, collisions and gas can all flatten a dwarf galaxy's centre, so a core alone cannot name the dark matter. Halo numbers and trends help.

2. L1 · Chapter

   ## [How a cusp or a core shapes a rotation curve](https://sandboxphysics.com/stories/dark-matter-small-scales/cusp-core-and-rotation-speed/)

   Build a cold dark matter halo from the NFW profile, compute its enclosed mass and circular speed, and see how a flat core lowers the inner rotation curve.

3. L2 · Chapter

   ## [How warm and fuzzy dark matter erase small ripples](https://sandboxphysics.com/stories/dark-matter-small-scales/erasing-small-scale-power/)

   Read a transfer function, turn a half-mode scale into a halo mass, and compute how much warm or fuzzy dark matter thins out small halos.

4. L3 · Chapter

   ## [Three ways to make a dark matter core](https://sandboxphysics.com/stories/dark-matter-small-scales/three-ways-to-make-a-core/)

   Derive the fuzzy soliton, the self-interacting isothermal core and the feedback core in one dwarf halo, then compare how each core changes with halo mass.

5. L3 · Method

   ## [Recompute the warm cutoff, the fuzzy cutoff and the soliton](https://sandboxphysics.com/stories/dark-matter-small-scales/recompute-cutoffs-and-a-soliton/)

   Check three dark matter fitting formulas against a frozen CLASS grid, a growth equation and an exact soliton, with scripts, outputs and failure cases.

6. L3 · Paper guide

   ## [Reading the Milky Way satellite limits on warm and fuzzy dark matter](https://sandboxphysics.com/stories/dark-matter-small-scales/reading-milky-way-satellite-limits/)

   A figure-by-figure guide to Nadler et al. 2021: how satellite counts give warm and fuzzy dark matter limits, and where those limits are soft.