Detecting Dark Matter with Imploding Pulsars in the Galactic Center

The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.

Figure 1

Bosonic DM nucleon scattering cross-section bounds for pulsar J0437-4715 outside the GC (black solid line), the newly discovered magnetar J1745-2900 (black dashed line), and the lower bound on these parameters assuming DM has collapsed millisecond pulsars ${10}^7$ years old at the GC (black dotted-dashed line) are shown. If bosonic DM has collapsed millisecond pulsars, its parameters will lie in the shaded region between these contours, except for the region below the no thermalization contour (dashed line, red), under which DM will not settle into the core of a pulsar. The upper dashed line indicates thermalization within ${10}^5$ years, the lower, ${10}^9$ years. The upper panel shows bosonic DM with very small self-interactions ($\lambda ={10}^{-30}$), while the bottom panel assumes bosonic DM with a small $\lambda |\varphi {|}^4$ term ($\lambda ={10}^{-15}$).

Figure 2

Curves for which fermionic DM will destroy 7 Gyr pulsars near earth, young pulsars 0.1 pc from the GC, and GC millisecond pulsars, are shown with conventions given in Figure 1. The parameter space shown is for fermionic DM with a Yukawa coupling ($\alpha =0.1$) to a light ($m_{\varphi }=10\mathrm{MeV}$) boson. DM masses $<100\mathrm{GeV}$ may be excluded by bullet clusters and the ellipticity of spiral galaxies [44].

Figure 3

This figure displays maximum pulsar age as a function of distance from the GC for a number of asymmetric bosonic DM models. The model for each curve is labeled in the format [Mass, ${\sigma }_{nX}({\mathrm{cm}}^2)$, $\lambda$]. The flat pulsar age distribution predicted for GeV DM (solid black line) is a signal that would appear for asymmetric bosonic DM in the 10 MeV-TeV range as a result of longer thermalization times in pulsars.