Universality in oscillation modes of superfluid neutron stars?

Abstract

It has been well established that the $f$-mode of relativistic ordinary-fluid neutron stars displays a universal scaling behavior. Here we study whether the "ordinary" $f_{\mathrm{o}}$- and "superfluid" $f_{\mathrm{s}}$-modes of superfluid neutron stars also show similar universal behavior. We first consider a simple case where the neutron superfluid and normal fluid are decoupled, and with each fluid modeled by a polytropic equation of state. We find that the $f_{\mathrm{o}}$-mode obeys the same scaling laws as established for the $f$-mode of orindary-fluid stars. However, the oscillation frequency of the $f_{\mathrm{s}}$-mode obeys a different scaling law, which can be derived analytically from a homogenous two-fluid stellar model in Newtonian gravity. Next the coupling effect between the two fluids is studied via a parameterized model of entrainment. We find that the coupling in general breaks the universal behavior seen in the case of decoupled fluids. Based on a relativistic variational principle, an approximated expression is derived for the first-order shift of the $f_{\mathrm{s}}$-mode squared frequency due to the entrainment.

32 pages, 14 figures; accepted for publication in ApJ

References in corpus (4)

• Upper limits on gravitational wave emission from 78 radio pulsars
• Quasi-Normal Modes and Gravitational Wave Astronomy
• Search for Gravitational Wave Bursts from Soft Gamma Repeaters
• Oscillations of General Relativistic Multi-fluid/Multi-layer Compact Stars

Cited by in corpus (3)

• A superfluid perspective on neutron star dynamics
• Quasi-normal modes of superfluid neutron stars
• Nonradial instabilities in anisotropic neutron stars