Dark-matter halo merger
= Dark-matter halo merger
A dark-matter halo merger joins previously distinct <dark-matter halos>. Orbital <angular momentum> can become internal halo spin, while escaping material carries away some mass and <angular momentum>. Halo mergers and accretion are important reasons that early <tidal torque theory> is only an approximate predictor of the spin of a later virialized remnant.