Neutron stars as dark matter detectors

It has been known for quite some time that neutron stars (NSs) can play a role in dark matter (DM) detectors due to many unique features of NSs. We apply these (previously developed) ideas to a specific form of the DM when it is represented by a composite object, rather than by a local fundamental field (such as WIMPs). To be more precise we consider the so-called axion quark nuggets (AQN) dark matter model, when the "nonbaryonic" dark matter in fact is made of quarks and gluons which are in dense quark phase (similar to the old idea of the Witten's strangelets). We argue that the interaction of the AQNs with NSs material may lead to many profound observable effects, which are dramatically different from the conventional picture when DM particles are represented by WIMPs. In particular, we argue that the AQNs may serve as the triggers for the magnetic reconnection to heat the NSs' surface. This effect may strongly alleviate (or even completely remove) the observed inconsistencies between the predicted and observed surface temperatures for many old NSs. This heating mechanism is always accompanied by the hard x-ray emission, which may serve as an indicator of the proposed mechanism.