Today's APOD https://apod.nasa.gov/apod/ap171031.htmlshows a simulation picture of the developing universe involving galaxy formations and dark matter thin threads. I am wondering if any PF participant can answer the following questions: 1. Why does dark matter form thin thread structures rather than clumps? 2. Do the simulations assume other processes in addition to gravity, such as the loss of orbital energy of ordinary matter via photons due to electromagnetic interactions? 3. Are there any similar simulation assumptions about non-gravity processes affecting dark matter?