Lighting the Universe with filaments

Abstract

The first stars in the Universe form when chemically pristine gas heats as it falls into dark matter potential wells, cools radiatively due to the formation of molecular hydrogen, and becomes self-gravitating. We demonstrate with super-computer simulations that their properties depend critically on the currently unknown nature of the dark matter. If the dark matter particles have intrinsic velocities that wipe-out small-scale structure, then the first stars form in filaments with lengths of order the free-streaming scale, which can be about 10^20m (~3kpc, baryonic masses 10^7 solar masses) for realistic "warm dark matter" candidates. Fragmentation of the filaments forms stars with a range of masses which may explain the observed peculiar element abundance pattern of extremely metal-poor stars, while coalescence of fragments and stars during the filament's ultimate collapse may seed the super massive black holes that lurk in the centres of most massive galaxies.