Multiple mountains on a pulsar: implications for gravitational waves and the spin-down rate

Abstract

A pulsar, i.e., a spinning neutron star, with a deformation could emit gravitational waves continuously. Such continuous waves, which have not been detected yet, will be very useful to study gravitational physics and to probe the extreme physics of neutron stars. While typically such waves from a pulsar are estimated considering an overall stellar ellipticity, there can be multiple irregularities or mountains in the stellar crust that the gravity of the star cannot smooth. In this paper, we consider this realistic situation and compute the strain, power, torque and the pulsar spin-down rate due to multiple mountains supported by the stellar crust. Here, we consider astronomically motivated mountain distributions and use the Brans-Dicke theory of gravity which has three polarization states: two tensors dominated by the time-varying quadrupole moment and one scalar dominated by the time-varying dipole moment. We also give the limiting results for general relativity.

Figures (6)

• Figure 1: Spin down rate due to scalar waves (top panel) and tensor waves (bottom panel) as functions of number ($N$) of mountains on the surface of a pulsar. The locations of mountains are randomly chosen, and mountains have the same ellipticity of $10^{-6}$.
• Figure 2: Similar to Figure \ref{['Fig:1']}, but the ellipticity of each mountain is randomly chosen between $0$ and $10^{-6}$.
• Figure 3: GW amplitude of scalar waves (top panel) and tensor waves (bottom panel) as functions of number ($N$) of mountains on the surface of a pulsar. The locations of mountains are randomly chosen on the equator and mountains have the same ellipticity of $10^{-6}$.
• Figure 4: Similar to Figure \ref{['Fig:h0-1']}, but the ellipticity of each mountain is randomly chosen between $0$ and $10^{-6}$.
• Figure 5: The variation of power emitted and spin-down rate due to two mountains as a function of the latitude ($\theta_1$) of the first mountain. The left top panel shows power emitted in transverse waves, the left bottom panel shows spin-down rate due to tensor waves, the right top panel gives power emitted in scalar waves, and the right bottom panel gives spin-down rate due to scalar waves.