Can Neutron stars constrain Dark Matter? (1004.0586v1)

Abstract: We argue that observations of old neutron stars can impose constraints on dark matter candidates even with very small elastic or inelastic cross section, and self-annihilation cross section. We find that old neutron stars close to the galactic center or in globular clusters can maintain a surface temperature that could in principle be detected. Due to their compactness, neutron stars can acrete WIMPs efficiently even if the WIMP-to-nucleon cross section obeys the current limits from direct dark matter searches, and therefore they could constrain a wide range of dark matter candidates.

Constraints on Dark Matter Properties from Neutron Star Observations

The paper "Can Neutron Stars Constrain Dark Matter?" explores the potential for neutron stars, as compact and dense astrophysical objects, to serve as probes for dark matter properties. It argues that the dense environments near neutron stars allow for the efficient capture and potential annihilation of dark matter particles, providing a unique platform for setting constraints on dark matter candidate characteristics.

Neutron Stars as Dark Matter Detectors

Neutron stars, given their high baryonic density, are well-suited for capturing Weakly Interacting Massive Particles (WIMPs), a popular dark matter model. The paper discusses how neutron stars can maintain observable surface temperatures due to the heating caused by dark matter annihilation. This heating effect is more pronounced in dark matter-rich environments, such as those near the Galactic center or within globular clusters.

The paper investigates the accretion and annihilation processes of WIMPs within neutron stars, proposing that the rate of accretion is dependent on both the dark matter density and WIMP characteristics like mass and interaction cross-sections. Crucially, even WIMPs with small elastic or inelastic cross-sections can be captured effectively by neutron stars due to their compact nature, thus offering opportunities for constraining a wide range of dark matter candidates.

Numerical Results and Key Findings

Observations of neutron stars with temperatures around $10^5$ K or lower can impose constraints on dark matter models. The paper provides numerical bounds for accretion rates and temperature predictions under several dark matter halo profiles. It highlights that the existence of old, yet relatively warm neutron stars could indicate heating from dark matter annihilation.

Theoretical calculations show how neutron stars can constrain dark matter when the interaction cross-section is significantly smaller than current direct detection limits. The paper suggests that for cross-sections on the order of $10^{-45}$ $\text{cm}^2$, neutron stars can still accrete a substantial amount of dark matter, impacting the thermal history and observable characteristics of the star.

Implications and Future Directions

The potential detection of anomalously high surface temperatures in neutron stars located in dense dark matter regions would support the existence of specific dark matter candidates. Conversely, observations of unexpectedly low temperatures could negate narrower dark matter models.

This approach to dark matter exploration highlights neutron stars as pivotal astrophysical laboratories. The paper encourages further observational studies targeting isolated neutron stars in regions of enhanced dark matter density, bringing astrophysical insights into dark matter research.

As observational techniques advance and data from neutron star systems improve, they could provide substantial contributions to understanding the properties of dark matter. This paper underscores the importance of combining astrophysical observations with particle physics models to navigate the complexities of dark matter research effectively. Future developments could involve advancements in both the precision of neutron star temperature measurements and the refinement of dark matter density profiles in various cosmic environments.