On the capture of dark matter by neutron stars

We calculate the number of dark matter particles that a neutron star accumulates over its lifetime as it rotates around the center of a galaxy, when the dark matter particle is a self-interacting boson but does not self-annihilate. We take into account dark matter interactions with baryonic matter and the time evolution of the dark matter sphere as it collapses within the neutron star. We show that dark matter self-interactions play an important role in the rapid accumulation of dark matter in the core of the neutron star. We consider the possibility of determining an exclusion region of the parameter space for dark matter mass and dark matter interaction cross section with the nucleons as well as dark matter self-interaction cross section, based on the observation of old neutron stars. We show that for a dark matter density of 10³ GeV/cm³and dark matter mass m_χ ≲ 10 GeV, there is a potential exclusion region for dark matter interactions with nucleons that is three orders of magnitude more stringent than without self-interactions. The potential exclusion region for dark matter self-interaction cross sections is many orders of magnitude stronger than the current Bullet Cluster limit. For example, for high dark matter density regions, we find that form_χ ∼ 10 GeV when the dark matter interaction cross section with the nucleons ranges fromσ_χn ∼ 10⁻⁵² cm² toσ_χn ∼ 10⁻⁵⁷ cm², the dark matter self-interaction cross section limit is σ_χχ ≲ 10⁻³³ cm², which is about ten orders of magnitude stronger than the Bullet Cluster limit.