The Digital Press

Galaxies like the Milky Way have fewer satellite galaxies than predicted by cold dark matter models, largely because many subhalos never formed stars. High-resolution simulations reveal that starless subhalos arise from early conditions that prevent gas cooling and star formation, rather than from supernova feedback or environmental effects.

Why it matters: Understanding why many subhalos lack stars resolves discrepancies between observed satellites and dark matter predictions.

The big picture: Starless subhalos form in regions with inefficient matter accretion, preventing gas from cooling and forming stars.

Stunning stat: Most subhalos in Milky Way-like galaxies are starless, matching observed satellite numbers.

Quick takeaway: Reionization's UV background heating blocks star formation in some subhalos, showing they are born starless, not made so.