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.