  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.
