Gravitational Waves from Compact Dark Objects in Neutron Stars

Dark matter could be composed of compact dark objects (CDOs). We find that the oscillation of CDOs inside neutron stars can be a detectable source of gravitational waves (GWs). The GW strain amplitude depends on the mass of the CDO, and its frequency is typically in the range 3–5 kHz as determined by the central density of the star. In the best cases, LIGO may be sensitive to CDO masses greater than or of order ${10}^{-8}{M}_{\odot }$.

Figure 1

Orbital radius $r$ in units of the NS radius $R_{\mathrm{NS}}$ (blue dashed curve), gravitational wave frequency $f_{\mathrm{GW}}$ (red curve, in kHz), and GW strain $h_0$ (solid black curve, arbitrarily scaled) for a $m_D={10}^{-3}{M}_{\odot }$ dark matter object in a circular orbit around, and then in, a NS of radius 12 km and mass $1.4M_{\odot }$ as a function time $t$. For $t>0$ the orbit of the dark object resides inside the NS.