Too massive neutron stars: The role of dark matter?. (arXiv:1208.3722v1 [astro-ph.SR])

Too massive neutron stars: The role of dark matter?. (arXiv:1208.3722v1 [astro-ph.SR]):
The maximum mass of a neutron star is generally determined by the equation of
state of the star material. In this study, we take into account dark matter
particles, assumed to behave like fermions with a free parameter to account for
the interaction strength among the particles, as a possible constituent of
neutron stars. We find dark matter inside the star would soften the equation of
state more strongly than that of hyperons, and reduce largely the maximum mass
of the star. However, the neutron star maximum mass is sensitive to the
particle mass of dark matter, and a very high neutron star mass larger than 2
times solar mass could be achieved when the particle mass is small enough. Such
kind of dark-matter- admixed neutron stars could explain the recent measurement
of the Shapiro delay in the radio pulsar PSR J1614-2230, which yielded a
neutron star mass of 2 times solar mass that may be hardly reached when
hyperons are considered only, as in the case of the microscopic Brueckner
theory. Furthermore, in this particular case, we point out that the dark matter
around a neutron star should also contribute to the mass measurement due to its
pure gravitational effect. However, our numerically calculation illustrates
that such contribution could be safely ignored because of the usual diluted
dark matter environment assumed. We conclude that a very high mass measurement
of about 2 times solar mass requires a really stiff equation of state in
neutron stars, and find a strong upper limit (<= 0.64 GeV) for the particle
mass of non-self- annihilating dark matter based on the present model.