Does dark matter not produce heat or radiation after a collision etc?
Or, we detect radiations having no generators?
It appears Dark Matter (DM) does not radiate any electromagnetic radiation, hence the 'Dark' part of the name. It does however appear to collect together due to gravity, hence the 'Matter' part. It appears to only very weakly interact with other types of matter during 'collisions' and therefore has no method of shedding momentum or energy in a collsion and does not therefore collapse as ordinary matter will under gravity.
The Bullet cluster is a great example of two amounts of DM passing through each other while the ordinary matter collides and is left in the middle.
The exact nature of DM is purely speculative at this moment in time; ATLAS at the LHC hopes to find particles that would fit the bill (supersymmetric neutrinos) but has yet to find any proof of these.