Why do we expect wimps to be distributed throughout galactic halos, rather than settled into the galaxy's disk?

The answer is that "since they do not interact with the electromagnetic force, they do not feel friction or drag and hence do not contract with the rest of the protogalactic cloud." WIMPs (Weakly-Interacting Massive Particles) are hypothetically constituted to dark matter. It is in their nature to be less interactive, so they are scattered throughout galactic halos and not focused into the galaxy's disk.

There is totally sun all the way down there.

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen